Monday, June18, 2018

Inspection, Repair, And Maintenance Of Wood Hulls

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Guidance on and Maintenance
of Wooden Hulls
August 1995
CHAPTER 1 DESIGN Introduction 11
B Acceptable Society Rules 11
C Good Marine Practice 11
A Introduction 21
B Plan Review 21
C Other Society Rules and Standards 21
D The Five Year Rule 21
A Shipbuilding Wood 31
B Bending Woods 31
C Plywood 32
D Wood Defects 33
E Mechanical Fastenings Materials 33
F Screw Fastenings 34
G Nail Fastenings 35
H Boat Spikes and Drift Bolts 36
I Bolting Groups 37
J Adhesives 37
K Wood Preservatives 38
B What to Look For 41
C Structural Problems 41
D Condition of Vessel for Inspection 41
E Visual Inspection 42
F Inspection for Decay and Wood Borers 42
G Corrosion Cathodic Protection 46
H Bonding Systems 410
I Painting Galvanic Cells 411
J Crevice Corrosion 412
K Inspection of Fastenings 412
L Inspection of Caulking 413
M Inspection of Fittings 414
N Hull Damage 415
O Deficiencies 415
A General 51
B Planking Repair and Notes on Joints in Fore and 51
Aft Planking
C Diagonal Planking 52
D Plywood Repairs 52
E Butt Joints in Planking 53
F Mechanically Fastened Scarfs 54
G Framing Repairs 56
H Decayed Frame Heads 57
I Treating Isolated Decay 57
J Sheathing of Existing Wood Hulls Construction Details
Navigation and Vessel Inspection Circular is the result of a joint effort between the Wooden Boat
Industry and the Coast Guard to provide the latest and most practical methods of wooden and repair Every effort was made to harness the collective
expertise and practical insight of
Coast Guard field inspectors and wooden boat builders shipyard repairers marine surveyors thanks goes to the following people who comprised the Joint
Guard Wooden
Boat Inspection Working Group and actively participated in the revision of NVIC 163
Mr Giffy Full Surveyor Brooklin Maine
Mr Edward McClave Consultant Noank Fred Hecklinger Surveyor Annapolis Maryland
Mr K T Smith Yorktown Virginia
Mr Bill Holland Builder DIberville Meade Gougeon WEST SYSTEM Developer Bay City Michigan
Mr Ernie Baird Repairer Port Townsend Kenneth Franke USCG Retired Surveyor San Diego CA
Commander Al Moore USCG Commandant Bill Uberti USCG Commandant Commander Marc Cruder USCG Commandant NVIC reflects the wooden boat building and
repair methods acceptable at the time of It is not meant to be the sole authority on this subject Survey and repair methods not
discussed in this NVIC which have proven themselves seaworthy should be forwarded to the Coast
Guard Commandant GMCO2 for consideration in any future A1
LIST OF FIGURES AND A Typical Wood Screw 35
Figure B Wood Screw Properly Inserted and Countersunk 35
Figure C Stray Current Corrosion 49
Figure D Bonding Systems 410
Table 41 The Galvanic Series of Metals in Seawater 417
Notes on the Use of the Galvanic Series Table 418
Figure E Common Forms of Scarfs 55
of common wooden boat words
see Annex C for illustrations of typical construction Construction Double diagonal planking system with the planks of both skins raking in the
same The spine of the hull from which the frames Rabbett The surface against which the side of a plank lies in a rabbetted member The of the
plank penetrate the back rabbett of a stem or sternpost the lower or inner of a plank penetrate the back rabbett of a keel or horn timber See diagram
Rabbett line Outer Rabbett Line
Apex Line Middle Rabbett Line Margin Line
Bearding Line Back Rabbett Line Inner Rabbet Line
Bearding Line
Rabbett Line
Back Rabbett
Appex Added weight either within or external to the hull added to improve the stability of a vessel or
bring it down to its designed lines
Balsa Sandwich End grain balsa wood used as a core between FRP Sawn Hardwood lumber in which the annual rings make angles of 30 degrees to 60
with the surface of the A thin flexible piece of wood
Beam A structural member supporting a load applied transversely to it The transverse members of a
deck framing system the width of a vessel
Beam Knee A gusset like member used to connect a beam to a Line The line formed by the intersection of the inside of the planking with the side or
face of
the Steam The process of forming a curved wood member by steaming or boiling the wood and
bending it to a form
Bilge Plank A strengthening plank laid inside or outside of a vessel at the bilges turn also known as
Bilge Strake An extra thick strake of side or deck Section Mast A hollow mast of round square or rectangular section made up of long strips
Timber knees placed horizontally between two fore ends of stringers to reinforce to the stem
Butt Block A short longitudinal piece of wood used to back up the connection of two plank That part of a vessels stern above her waterline which
overhangs or lies abreast of the stern
post the Lines Lines representing fore and aft vertical sections from the centerline The curve of a deck Frames Frames whose plane of support is
not perpendicular to the fore and aft Fore and aft finished piece along the topside of an open boat often improperly called a covering board margin
plank or plank sheer in a decked The fore and aft members of the deck framing Planked Smooth skinned planking whose strakes run fore and calking
Cotton oakum or other fiber driven into planking seams to make them An inner skin of the hull often used to add strength in boats having sawn frames
In some
cases the ceiling is not structural but merely serves to line the hull for decorative purposes or for ease
Chain Plate Shroud Plate A flat strip of metal fastened through the hull either from inside or
outside to which the lower ends of the shrouds are A lengthwise separation of the wood that usually extends across the rings of annual growth
and commonly results from stresses set up in wood during The line of intersection of the bottom with the side of a vee or flat bottomed The fore
and aft member at the sheer line of the vessel to which the deck beams usually Planking Lapstrake in which the adjacent planks overlap like
clapboards of a Fastening Securing a nail or rivet by placing a rove washer over the inboard side and then
bending the fastening over it In many cases they are simply bent over by driving them against a
backing iron causing them to reenter the Built See clench Mast A protective piece usually canvas covering the mast wedges where the mast enters
Bent frames Frames which are bent on forms and after shaping are fitted to the vessel
Cold Molded A method of boat construction using a male mold over which layers of thin wood
andor plywood are diagonally laid and glued together Can be covered with epoxy or FRP
Cove Line A hollowed out decorative line found along the sheer of a Board A plank used as a washboard or plank sheer along the outer edge of the
See The forward edge of the stem at the Rise The amount the bottom rises from keel to chine most properly applied to Vee but also used in
reference to the rising bottom of round bottom A stout disk of hard wood strapped with rope or iron through which holes usually three
are pierced for the reception of lanyards They are used as blocks to connect shrouds and chain The vertical structure built up from the keel to
support the cant frames at the stern or
stem longitudinal timbers of a vessels structural backbone which lie entirely outside the and horn timber rabbett lines
Decay The decomposition of wood substance by fungi
1 Advanced or typical The older stage of decay in which the destruction is readily
recognized because the wood has become punky soft and spongy stringy ringshaked
pitted or crumbly Decisive discoloration or bleaching of the rotted wood is often
2 Incipient The early stage of decay that has not proceeded far enough to soften or
otherwise perceptibly impair the hardness of the wood It is usually accompanied by a
slight discoloration or bleaching of the wood
Deck Head The underside of the Planking Planking laid on an angle to the The actual weight of a boat as it displaces its weight when afloat not
to be confused
with admeasurement Pins Bolts A long fastening driven pin or threaded bolt to receive end nuts used for joining
heavy timbers such as horn timbers and stern frames also used to fasten and reinforce wooden panels
on edge such as rudders and centerboard trunks
Dry Rot A term loosely applied to any dry crumbly rot but especially to that which when in an
advanced stage permits the wood to be crushed easily to a dry powder The term in actually a
misnomer for any decay since all fungi require over 20 moisture to Wooden block or wedge used to fill the void in a badly made butt or joint a
graving piece
or repairing patch in a deck filler shim short Lumber Lumber that has been sawed so that the wide surfaces extend approximately at
right angles to the annual growth rings Lumber is considered edged grained when the rings form an
angle of 45 degrees to 90 degrees with the wide surface of the Amount required to be cut away from the edge of a plank in fitting Nailed A method
of fastening a strip plank to adjacent Building one piece of timber on another for strength or finish Keel Sacrificial batten added to the keel to
protect the keel from grounding and from eg worm shoe
Faying Joining closely Lumber Lumber that has been sawed in a plane approximately perpendicular to a radius
of the log Lumber is considered flat grained when the annual growth rings make an angle of less than
45 degrees with the surface of the piece
Floor or Floor Timber A transverse structural member lying across the keel and tying the frames on
either side of the keel together The central futtock or futtocks of a sawn frame lying across the
keel Floor timbers join both sides of a vessel together and make up the substructure for external engine beds and mast Planking laid on top of the
floors to provide a walkway Also known as the The transverse structure at each section giving form to the hull Frames connect to the keel or
keels on and to the clamp or shelf at the sheer Also known as Port Any direct opening through the vessels bulwark or hull to quickly drain overboard
that has been shipped on exposed Curved parts or sections of transverse frames extending from the floor timbers to the The strake of planking
nearest the keel
Green Freshly sawed lumber or lumber that has received no intentional drying unseasoned The
term does not apply to lumber that may have become completely wet through Beam A built up beam of short heavy timbers used to shape a round Any
piece that is used to join or strengthen the joint of two other Knee A strengthening bracket used between frames and deck The wood extending from
the pith to the sapwood the cells of which no in the life processes of the tree Heartwood may be infiltrated with gums resins and that usually make
it darker and more decay resistant than Timber One or more timbers forming the main support for an overhanging stern and extending
aft from the upper end of the stern post Also used for timber connecting the shaft log and body post
with the rudder post
Horse n The form upon which a small boat is built
Horse v To drive home as to horse Frame A frame which after being softened by heat is bent into shape as it is The junction of two pieces of wood
or veneer
Butt Joint An end joint formed by abutting the squared ends of two pieces Because of the
inadequacy in strength of butt joints when glued they are not generally used
Edge Joint The place where two pieces of wood are joined together edge to edge commonly
by gluing The joints may be made by gluing two squared edges as in a plain edge
joint or by using machined joints of various kinds such as joints
Scarf Joint An end joint formed by joining with glue and mechanical fastenings the ends of
two pieces that have been tapered or beveled to form a sloping plane surface to
the same length in both pieces In some cases a step or hook may be machined
into the scarf to facilitate alignment of the two ends in which case the plane is
discontinuous and the joint is known as a stepped or hooked scarf joint or scarf
joint with nib
End Joint The place where two pieces of wood are joined together end to end commonly by
scarfing and gluing
Lap Joint A joint made by placing one piece partly over another and bonding the overlapped
Starved Joint A glued joint that is poorly bonded because insufficient quantity of g lue
remained in the joint Starved joints are caused by the use of excessive pressure
or insufficient viscosity of the glue or a combination of these which result in
the glue being forced out from between the surfaces to be joined This term
should only apply to epoxy glues Joints made with other waterproof or water
resistant glues like resorcinol and brown glue should be
starved for maximum An inner keel usually laid over the floors and through bolted to the keel
Kerf Kerfing To cut or make a channel with a saw blade
Kiln Dried As in timber refers to forced hot air circulation through a chamber to dry the wood
King Plank The centerline plank of a deck
Knee See Hanging Knee
Knot That portion of a branch or limb which has been surrounded by subsequent growth of the wood
of the trunk or other portion of the tree As a knot appears on the sawed surface it is merely a section
of the entire knot its shape depending upon the direction of the See Clench A hole allowing the free passage of water from one area to Vitae A
hardwood used for deadeyes and propeller shaft Iron A large caulking iron used to drive oakum into plank seams
Mast Partners Carlins between deck beams to strengthen the area where the mast passes through Measurement of a plank or timber from inboard to
outboard ie parallel to the plane in
which the member lies opposed to siding measured at right angles to such plane Thus the molding of
a frame is measured in the thwartship direction while that of a stern piece is its cross fore and aft
Nib The squared off end of a tapered piece such as a scarf
Noble Metal A metal most resistant to deterioration due to galvanic action the cathodic A caulking material of tarred Stiffening or supporting
pieces fitted in way of the passage of a mast through a deck See
Mast The filling of the seam with seam putty pitch tar or other type of seam sealant after Pocket An opening extending parallel to the annual
growth rings containing or that pitch either solid or Strips of wood that form the skin of a boat Sheer See Capping
Any substance that for a reasonable length of time is effective in preventing and action of woodrotting fungi borers of various kinds and harmful
insects wood
Prick Post An outer post supporting an outboard Knees Lateral brackets similar to the breast hook used to join the sheer shelf or clamps to Lumber
Another term for EdgeGrained A longitudinal channel or groove in a member which received another piece to make a Two or more structural members
working and becoming loose structural deformation of section of a ships hull A vessel is said to be racked if when viewed end on it appears to be
leaning or tilting over to one side Symptoms of racking generally appear at the junction of the frames
with the beams and A formaldehyde resin to which a powder hardener is added to form a strong wood glue
Rib See Post Any post well attached to the vessels structure to take excessive loads used as a The dimensions of all structural parts used in
building a boat A full scantling vessel is of
maximum required structural scarph n A joint by which the ends of two structural pieces of timber are united so as to
form a continuous piece a lapped joint made by beveling off notching or otherwise cutting away the
sides of two timbers at ends and bolting riveting or strapping them together so as to form piece without increase in sectional area at the joint
Scarf v To join the ends of two timbers so as to form a continuous piece in appearance the joining
of wood by sloping off the edges and maintaining the same cross section throughout the A pipe or tube leading down from a deck and through the hull
to drain water A separation along the grain the greater part of which occurs between the rings of
Sheer Sheer Line The intersection of the deck and the hull the longitudinal sweep of the deckline
from the stem to the sternpost upward at the ends in traditional designs and downwards at the ends Strake The top or uppermost plank in a hull
Shelf Line of timbers bridging and thus stiffening frames but chiefly for supporting the end of the A misnomer for the wood boring mollusk Teredo
which feeds on wood but different marine borer the Limnorae is also misnamed Generally the sawn or planed thickness of the planks or timbers from
which wood members
are shaped or cut See As in sister frame or sister keelson A member attached to or laid alongside an original member
to strengthen it either as an original construction technique or as a The edge curve in a strake of A separation of the wood with the grain due to
the tearing apart of the wood As in spline planking A thin tapered strip of wood glued and hammered into carvel plank
seams which have become enlarged and spill caulking A discoloration in wood that may be caused by such diverse agencies as or chemicals The term
also applies to materials used to impart color in In the shell planking toward the ends of a vessel a strake introduced as a single continuation of
two tapering strakes One of usually the shorter or narrower of the two planks which are butted into
a single plank as double continuation or as the short piece notched into a larger plank to add width not
available on one board
Stern Frame The frame work around the inside of the A softwood dowel driven across a lap scarf or butt joint in the backbone structure or
elsewhere to prevent seepage of water into the hull any contrivance to accomplish this One of the rows or strips of planking constituting the
surface of the hull
Strip Planking Carvel construction where each plank is edge nailed to the adjacent A timber rail around the aft deck of a vessel
Treenail Trunnel A wood dowel used as a fastening often fitted with a wedge in the dowel end to
hold it in place Dense wood such as locust is used for the dowel
Wane A defective edge or corner of a board caused by remaining bark or a beveled end
Warp Any variation from a true or plane surface Warp includes bow crook cup and twist or The mechanical or chemical and discoloration of the
surface of wood
caused by exposure to light action of dust and sand carried by winds and alternate shrinking and
swelling of the surface fibers with the variation in moisture content brought by changes in the weather
Weathering does not include decay
Welt A strip of wood fastened over a flush joint or seam for strengthening purposes a seam A caulking material such as oakum or cotton used to
wrap a fastening in order to protect it
from Shoe A piece of wood placed at the bottom of the keel to protect the keel from
marine borers
CHAPTER 1 DESIGN Watercraft have evolved over centuries of trial and error to the more modern state of the art
vessels we are now familiar with Wood as a boat building material is still used in many parts of the
world as the most readily available easy to work repairable material for marine applications Even
with the advent of composites fiber reinforced plastic FRP and lightweight metals wood will for
many years to come continue to be a major factor in the design of boats
Lloyds Register of Shipping Rules and Regulations for the of Yachts and Small Craft
is the standard adopted by reference in Coast Guard regulations for the design and construction of
wooden small passenger vessels Lloyds Rules apply to vessels of up to 50 meters 164 feet
scantling length
Other society standards may be accepted on a casebycase basis
No single publication contains all the innovations found in the design of wooden vessels This
circular and the readings referenced in Annex R form a basis of good marine practices from which
owners designers builders inspectors and surveyors can along with experience maintain the
highest level of small passenger vessel safety
Annex C contains several illustrations of typical construction details An index of these can be found on page C1
A This chapter is intended as a general reference and guide for submitting the plans for a proposed
vessel to the Coast Guard It is not a complete text on naval architecture or a commentary on
society rules Plans should be submitted in accordance with the appropriate
regulations to the Marine Safety Center MSC in PLAN REVIEW
1 Plans for small passenger vessels of wooden construction are generally reviewed by the local
Officer in Charge Marine Inspection OCMI For vessels over 65 feet in length andor vessels
incorporating novel designs or not entirely addressed by acceptable Society Rules plan review will be conducted by the MSC
2 Lloyds Rules and Regulations for the of Yachts and Small Craft should be used
as a reference for designs as well as application to existing vessels
1 Direct reference to Lloyds Rules is based on the familiarity that Coast Guard inspectors and
technical personnel have with reviewing a vessel designed to those standards This does not
prevent a design from being based on the rules of another society or on some
other standard The burden of proof rests with the designer to show with thorough
engineering documentation and logic that a proposed vessel meets a level of safety at least
equivalent to that prescribed by Lloyds Rules
2 Another useful historical reference that may be used as a plan review guide is Merchant
Marine Safety Instruction 1460 dated 14 April 1960 This instruction contains scantling
tables for 500 wooden TBoats up to 60 feet in length which have been approved for routes
ranging from rivers to oceans The scantlings in this reference are from a sampling of vessels
certificated based on years of satisfactory service similar to the present Five Year Rule noted
1 Definition The Five Year Rule is defined as
When scantlings differ from such standards and it can be demonstrated that craft
approximating the same size power and displacement have been built to such scantlings and
have been in satisfactory service insofar as structural adequacy is concerned for a period of at
least 5 years such scantlings may be approved A detailed structural analysis may be required
for specialized types or integral parts thereof for meeting this rule are made
for each case on individual basis by the OCMI
2 Burden Of Proof The burden is upon the designer or owner to show the similarities between
the proposed vessel and an existing vessel The Coast Guard approving authority may need
documentation showing the similarities in size power displacement and scantlings and may
conduct a survey andor underway check of the similar vessels performance in the anticipated
operating area Scantlings can vary greatly for similar sized wooden vessels depending on
materials used
3 Satisfactory Service The service life of small passenger vessels vary greatly depending on
location maintenance and use An inner harbor tour boat experiences a vastly different service
environment than does a deep sea party fishing vessel and is normally designed quite
differently An existing vessel used as a basis for a proposed new vessel should have
experienced at least the same operating environment planned for the new vessel for five years
showing satisfactory service A similar relationship of experienced service to expected service
should be presented to the OCMI for an existing vessel changing service into Coast Guard
Wood is an engineering material Douglas Fir Southern Yellow Pine long leaf and White Oak
furnish most of the wood used for boat and shipbuilding in the United States Of these Douglas
Fir is the predominant choice due to availability and relatively rapid growth
1 When requirements call for strength moderate to good decay resistance and ability to hold
fastenings well frames keels stems etc the following woods are most commonly used
Douglas Fir
Southern Yellow Pine long leaf
Western Larch
White Oak
2 Where light wood which is easy to work and is warp and decay resistant is required
planking etc the following woods are most commonly used
Cedar Port Orford Northern White Western Red and Alaska
Tangile Philippine hardwood
3 Where light easily worked and strong woods of moderate to low decay resistance are
required the following woods have found favor
Sitka Spruce
Western Hemlock
White Pine
Yellow Poplar
There are many other varieties suitable for boat use These are listed together with their
properties in The Encyclopedia of Wood and Wood A Manual for its use as a Shipbuilding
Material References 1 and 10
Unseasoned White Oak is the choice bending wood It bends readily and is high in decay
resistance Red Oak Hickory Rock Elm White Ash Beech Birch and hard Maple also bend
readily but do not have the decay resistance of White Oak White Oak and its best substitute
Rock Elm are expensive and hard to obtain but do the best job For a further discussion of the
effects of bending and bending ratios of various types of woods see Bent Frames Wooden
Boat No 86 page 87
It is important to remember that bending woods are unseasoned and therefore should show a
moisture content over 15 18 is desirable Attempting bends with dry wood results in
cracks across the grain particularly in hulls with sharp bends at the turn of the bilge
Plywood is a built up board of laminated veneers in which the grain of each ply is
perpendicular to the ones adjacent to it Its chief advantages lie in more nearly equal strength
properties along the length and width of the panel resistance to change in dimensions with
moisture content and resistance to splitting Major disadvantages are low decay resistance and
the difficulty of painting it properly
Plywood is excellent where strength is needed in more than one direction and where the
relatively large size of the panels available can be utilized It is no stronger than the wood from
which it is made and is not a cureall for wood structural problems
Plywood is made from several types of wood and in many different types and grades In
general type of fir plywood or its equivalent technical or Type 1 hardwoods
are the only plywoods acceptable for use as hull planking These plywoods are identical with
ordinary Exterior type in that they are bonded with waterproof glue by a process using heat
and pressure Their advantage lies in the fact that the interior plies contain few gaps and thus its
strength ability to hold fastenings and resistance to decay are much higher than Exterior
Marine plywood is more expensive than Exterior but provides additional safety and
Fir plywood is graded according to the appearance of the exterior veneers These grades run
from grade N intended for natural finish and grade A suitable for painting down through
grade D the poorest quality Each side is graded For example a panel may be graded
Marine Exterior AB where Marine Exterior refers to the type of bonding used and the
allowable defects in the inner plies while AB refers to the appearance of the two sides of the
Marine plywood is usually available only in appearance grades BC and better The strength of
the wood is indirectly reflected in the grading since the poorer grades have openings splits
pitch pockets and other defects which adversely affect strength and decay resistance
All plywood is marked with its This may appear on the panel back
on its edge or both Marine plywood is clearly marked Marine
Wood being a natural material is not uniform in quality and is subject to defects Some of
these affect only the appearance of the wood Others affect the strength of the wood and are of
Boat building and repair craftsmen carefully select each piece for the intended use Often a load
of timber even milled from the same tree will display a variety of defects Wood with knots
checks excessive warp splits and pitch pockets should be rejected for use particularly in hull
Mechanical fastenings should be of material suitable for the service intended Ferrous fastenings
should be hotdipped galvanized Among the usual nonferrous types brass is not acceptable in
salt water applications as it will corrode from de zincification and is inherently soft and weak
Caution should be used in selecting fastening material because of the problem of galvanic action
which can arise if dissimilar metals are used close to one another A bronze washer used with a
steel bolt will result in the eating away of the steel Proper selection of fastening materials will
significantly prevent corrosion and thereby extend their service life
Marine applications of stainless steel alloys are subject to a phenomenon
known as contact corrosion or more commonly crevice corrosion Stainless steels which are in
contact with each other or placed in tight joints nuts and bolts swage connections standing
rigging or used to fasten wood planking below the waterline corrode at an alarming rate The
vehicle of crevice corrosion is electrolytic cell formation If the stainless steel is unable to
naturally form a thin film of chromium oxide to shield the material from attack corrosive liquids
such as salt water are able to establish electrolytic cells with chloride ions and corrosion takes
place In short stainless steel depends on oxygen to provide protection against crevice
Grade 316 L passive stainless steel is the most accepted material for marine applications due to
the introduction of molybdenum to the alloy For example grade 304 stainless steel has 18
chromium and 8 nickel in the alloy while grade 316 L has 18 chromium and 10 nickel and
3 molybdenum Grade 304 is quite susceptible to crevice corrosion when employed in tight
spaces and unable to generate chromium oxide The 316 L material will last longer in the same
Chandlers usually stock only brass and stainless steel both being very unsuitable for underwater
fastenings The grade of stainless is rarely mentioned and is often only Type 304
Generally stainless steel fasteners should not be used underwater However they are used quite
frequently but only if all of the following conditions are met will they be a Austenitic grade at least Type 304 preferably Type 316
b Not passing through wet wood
c Ample sealant under the head and in between mating surfaces
d The item to be fastened is less noble than stainless ie all the copper alloys and
with some risk of hole enlargement steel and iron
Note Condition b indicates that stainless wood screws should never be used
The choice of stainless steel fasteners below the waterline should be carefully considered based
on the water salinity grade of stainless steel fastener available and material of other fasteners
and fittings in the hull Stainless steel may be subject to varying degrees of accelerated crevice
corrosion For more information see Metal Corrosion in Boats Reference 13
The number size type and spacing of fastenings for various applications are given in Lloyds
Rules and Regulations for the of Yachts and Small Craft Part 2 Chapter 4
A general guide for use of the various types of fastenings follows
1 Lead Holes Lead holes for wood screws should be about 90 of the root diameter of the
screw for hardwoods and about 70 of the root diameter for softwoods For large screws
and for hardwoods a shank hole of a diameter equal to the shank of the screw and of a
depth equal to the shank may be used to facilitate driving Lag screws should always have a
shank hole
The lead hole for the threaded portion of a lag screw should have a diameter of 6585 of
the shank diameter in oak and 6075 in Douglas Fir and Southern Pine with a length equal
to the length of the threaded portion Denser woods require larger lead holes and the less
dense require smaller holes For long screws or for screws of large diameter lead holes
slightly larger than those recommended here should be used The threaded portion of the
screw should be inserted by turning and not by driving with a hammer
Where possible screws should be selected so that the unthreaded shank penetrates the joint
for greatest strength and corrosion resistance and to facilitate the drawing together of the
members In this case the shank hole shall extend the full length of the shank If conditions
prevent the shank from extending through the joint the shank hole shall extend completely
through the member containing the head to prevent threads from engaging in that member
which might prevent the joint from drawing up
Figure A Typical Wood Screw
Figure B Wood Screw Properly Inserted And Bung
2 Lubricants Suitable lubricants such as wax grease or heavy paint but never soap should
be used on screws especially in dense wood to make insertion easier and prevent damage
to the screw
3 Depth Penetration of the threaded portion for at least a distance of 7 screw diameters for
hardwoods and 1012 in softwoods is required for maximum holding power
4 Loading If possible screws should be placed so that they are loaded across the screw and
not in the direction of withdrawal
The spacing end distance and edge distances for wood screws should be such as to prevent
splitting the wood Lag screws should follow the rules for bolts For further information
concerning wood screws see Wooden Boat Issue 54 55 Reference 17
Hot dipped galvanized cut boat nails have traditionally and are still being used in boat building
Barbed or annular ring nails have been successful and are suitable depending upon their
application usually smaller scantling vessels Smooth thinly coated or plated nails with small
irregular heads and long tapered shanks such as horseshoe nails and ordinary cut nails ie
hardwood flooring nails will not provide sufficient holding power and should not be used In
addition wire nails are not acceptable for hull 35
1 Lead Holes Lead holes for nailed joints may be 34 of the diameter of the nail without
causing loss of strength
2 Types Of Load If possible nails should be loaded across the nail and not in the direction of
withdrawal This is especially important in end grain
3 Spacing Of Nails The end and edge distances and spacings of the nails should be such as to
prevent splitting of the wood
1 Lead Holes Lead holes for boat spikes should be the size of the short dimension of the
spike and should extend approximately 75 of the spike depth The lead holes for drift
bolts should be slightly less than the bolt diameter and of a depth equal to the bolt length
2 Type Of Load Where possible spikes and drift bolts should not be loaded in withdrawal
This is especially important in end grain
3 Insertion A clinch ring or washer may be used under the head to prevent crushing of the
wood Spikes should be driven with the edge of the chisel point across the grain to avoid
splitting the wood
4 Spacing of Spikes and Drift Bolts The end distance edge distance and spacing of the
spikes should be such as to avoid splitting the wood
5 Bolts Bolt holes should be of such diameter as to provide an easy fit without excessive
clearance A tight fit requiring forcible driving of the bolt is not 6 Placement Of Bolts In Joint The center to center distance between bolts in a
row should be
not less than four times the bolt diameter
The spacing between rows of bolts should be 5 times the bolt diameter for a bolt whose
length from the bottom of the head to the inner side of the nut when tightened is 6 times the
bolt diameter or longer For short bolts this distance may be decreased but in no case
should be less than 3 times the bolt diameter
The end distance from the end of a bolted timber to the center of the bolt hole nearest the
end should be at least 7 times the bolt diameter for softwoods and at least 5 times the bolt
diameter for hardwoods These requirements should be relaxed where necessary in the case
of bolted planking butts to allow the front row of fastenings on each side of the butt to be
The edge distance from the edge of the member to the center of the nearest bolt hole
should be at least 1 12 times the bolt diameter For bolts whose length is over six times
their diameter use one half the distance between bolt rows and in no case below 1 12 times
the bolt diameter
For perpendicular to the grain loadings joints at right angles the edge distance toward
which the load act should be at least 4 times the bolt diameter
In general all groups of bolts should be symmetrical in the members The individual fasten ings
should be offset slightly as necessary to avoid placing more than one on the same grain
1 Washers The importance of washers especially under the heads of fastenings which may be
loaded in tension either because of external stresses or because of swelling stresses cannot be
overstated The weak link in most wood structures is not the tensile strength
of the wood or of the fastenings nor the withdrawal resistance of threaded fastenings The
weak link is almost always the crossgrain crushing strength of the wood
under the heads of the fastenings Care should be exercised in drawing nuts down on the
bolts too tight and crushing the wood
2 Wickings A suitable wicking should be fitted in way of the faying surface of the joint at each
through bolt subject to moisture
Household glues having low moisture resistance have tendencies towards early joint failure and
should be avoided in marine Resorcinol and resin type marine glues have been used for many years and are
satisfactory for most new construction and repair applications Resorcinol age hardens and
becomes brittle and inelastic over time and should be limited to rigid surfaces where shear
vibration and impact forces are unlikely
Ureatype adhesives such as Weldwood Plastic Resin glue are available in water mix onepart
and twopart mixes Use of ureas requires special care particularly with the two
part system as unlike epoxy resins the urea is applied with resin on one surface and the hardener
on the other Clamp pressure is then applied and the cure begins
Epoxy resins are available for a wide variety of marine applications and have been found to
provide excellent adhesion in all areas of boat building In the early 1960s epoxy adhesives were
introduced to western boat builders by the Gougeon Brothers of Bay City Michigan through
their registered trademark WEST SYSTEM Epoxy resins are two part adhesives and depend
on accurate mixing ratios to yield high strength joints Epoxy is also an excellent filler material
when thickened to high or low density with micro fibers micro balloons or colloidal silica
Not all woods are easily joined Wet wood above 18 moisture content is difficult to glue
Normal seasoned wood of most species can be glued Strong joints can be made bonding either
face or side grain of the wood These joints can be very nearly as strong as the wood itself It is
impossible to join end grain with glue and get joints which are even 20 as strong as the wood
A scarf or some other form of joint which gives a surface approaching side grain condition must
be used where end connection is desired
As with any chemicals the instructions must be carefully followed Curing
temperature and surface condition are important The temperature must be about 70 degrees
Fahrenheit or higher for a full cure of resorcinol resin glue Faying surfaces should be well fitted
Smooth surfaces make the strongest joints with resorcinol however a roughened surface for
epoxy joints is generally helpful in improving bond strength especially with hardwoods such as
K WOOD The use of wood preservatives is not required However their use in wood under severe
service conditions may pay for itself many times in decreased decay and borer attack and thus
decreased repair and replacement costs Their proper use should be encouraged since it
increases the chance of the vessel remaining sound until her next inspection and thus contributes
to maintaining a reasonable standard of safety
Wood preservatives used for protection against decay fungi and marine borers either kill the
organism or prevent it from growing For marine use the preservative must offer no toxic
hazard to the crew must be free from objectionable odors and must be able to remain in the
wood and do its work in the presence of moisture No known wood preservative is ideal for
marine use but certain ones have proved effective for specific There are two general classes of wood oil soluble and water soluble Both have
been used in the marine industry
1 Oil Soluble Preservatives
A Coal Tar Creosote One of the most effective of the oil soluble preservatives is coal tar
creosote This preservative is highly toxic to wood attacking organisms is relatively
insoluble in water and is easy to apply It has a distinctive unpleasant odor is somewhat
of a fire hazard when freshly applied and causes skin irritation in some individuals Its
main disadvantage is that it is a hazardous material to the environment and thus has
become unavailable for boat building applications However some older vessels with
deadwood keel stems and heavy timbers which were originally treated with creosote
are still in service
B Copper Naphthanate Solutions Copper naphthanate solutions form one of the most
used groups of marine wood A three percent solution equivalent to one
half of one percent copper by weight provides good protection against decay when
properly applied The protection afforded against marine borers is slight Wood treated
with copper naphthanate is a distinctive green color Much of the treated wood which
can be purchased is preserved with copper naphthanate The paintability glue bonding
ability and structural stability of the wood is only slightly affected by the copper salts
These properties will vary however depending upon the oil used as a solvent It is
important to note that this substance poses a serious health hazard to humans Full body
protection should be worn during C Solutions Penta solutions have proven satisfactory for marine
use Field tests have shown that a 5 solution offers adequate protection against decay
when proper application techniques are used Little if any protection against marine
borers is provided
does not give wood any distinctive color In itself it affects the
of wood very little The final effect of the preservation treatment on
physical depends upon the petroleum solvent used solution remains effective for approximately 23 years before it begins to break down
2 Water Soluble Preservatives
A Water Soluble Copper naphthanate and penta are often combined with
water repellents These repellents aid in stabilizing the moisture content of the treated
wood This is a material aid in reducing the chance that decay growth conditions will
occur In order to be effective these solutions should contain no less than 5
or 2 copper in the form of copper B Solvents Almost any petroleum product from mineral spirit to used engine oil can be
used as a vehicle for the preservative depending upon local conditions In general the
heavier high viscosity residuum types offer the best retention The choice of solvent is
usually a compromise of paintability and initial cost
C Water Waterborne preservatives include zinc chloride tanalith copper
arsenite chromated zinc arsenate and many others Their major applications are those
in which the leeching out of the preservative by moisture is not a problem In general
these preservatives have not proven satisfactory for severe marine service Some
preserved wood obtained for repair use may have been pressure treated with one of
these It can give satisfactory service if care is taken to use it in a location
where it is protected from the action of rain and sea water
3 Methods Of Treatment
A Pressure Treatment In the commercial treating of wood a method utilizing high
pressure is often used This method requires expensive equipment and is seldom seen in
a boat yard Nonpressure treatments available to the boat yard are brushing cold
soaking and various types of hot and cold bath processes
B Brush Treatment The simplest way of applying a preservative solution is to brush it on
Every crack and check must be flooded with preservative if the treatment is to be
effective Small pieces such as butt blocks can be dipped into the Solutions of or copper naphthanate available commercially have
proved effective when used in this way
Penta stock solutions are available in what is know as 15 and 110 strengths ie the
solution must be diluted one part of solution to five or ten parts of solvent to achieve a
normal wood preserving solution These stock solutions are used without dilution
for applications such as preserving cracks holes resulting from old fastenings and
coating joints and hard to get spots Care must be exercised since wood are toxic When using the brushon method the entire surface must be
C Soaking Cold soaking in copper naphthanate or penta solutions for periods of up to
48 hours provides much better retention of the preservative than does a brushing An
even better method consists of heating the wood in a hot preservative bath and then
transferring it to a cold bath of preservative The heating causes the air entrapped in the
wood to expand The sudden cooling sets up a vacuum which aids preservative
Preservative solutions or other chemicals which release copper ions into wood or into
the bilgewater should be avoided in vessels containing ferrous fastenings Copper ions
are more stable than iron and will spontaneously plate out on steel or on zinc coatings
replacing equal numbers of iron or zinc ions which go into solution replacement
corrosion While the amount of direct wastage of iron or zinc from this mechanism is
likely to be minimal the presence of copperplated regions on the surface of the steel
fittings cause them to become small isolated galvanic cells The further corrosion of the
steel or galvanizing may be significantly increased by the presence of copper surface
Copper naphthanate Cuprinol Chromated Copper Arsenate CCA and Ammoniacal
Copper Arsenate ACA wood preservatives are one common source of copper ions in
the wood or bilgewater Another source is the addition of chemical treatments to
bilgewater A traditional solution to the problem of sour bilges due to generation of
hydrogen sulfide gas by bacteria breaking down spilled diesel fuel is to dissolve copper
chloride crystals in the 310
Intelligent inspection of wooden vessel construction requires knowledge and judgment
Inspection is made to determine that the vessel is safe and has a reasonable chance of remaining so
until the next scheduled inspection A good basic knowledge of wood construction and the
deficiencies to which it is susceptible is WHAT TO LOOK FOR
Problems in wooden vessels group themselves into three categories
1 Time
a Decay
b Wood Borers
c Corrosion
2 Stress
a Cracks
b Broken members
c Failure of fastenings
d Failure of caulking
3 Damage
a Hull damage due to collision grounding or to normal wear and tear
In wooden vessels structural problems develop in nearly new vessels as well as in older ones
especially that caused by decay and wood borers can occur with surprising
rapidity Boats which have been free of such infestations can become infected with slight changes
in service area or operation Fastening problems in new wooden vessels can also develop as a
result of several types of corrosion
Poor selection of wood structural materials or lack of ventilation will often make themselves
known in the first year of a vessels service life That the vessel was sound at its last inspection
has less bearing on the present condition of a wooden vessel than on one of steel
If practicable inspect the vessel out of the water with the interior of the hull opened up as much as
possible The bilges and forepeak should be dry and reasonably clean Excess tackle tools and
gear which might interfere with proper inspection should be cleared away This is not always
possible however hard to inspect and thus hard to maintain areas should not be missed
Where the interior of the hull has closely fitted ceiling or paneling sufficient access should be
provided to allow examination of the interior at selected locations This can be accomplished on
lighter scantling vessels by cutting inspection openings in the ceiling which will also aid in
providing ventilation to combat dry rot On heavy timbered vessels borings or core samples may
be used to show the condition of hidden structures Apparent soundness of the ceiling should not
be taken as indicative of soundness beneath
In some cases access for frame inspection may be made by removal of andor
garboard planks for inspection from the outside In any case visual inspection must be
accomplished to ascertain conditions under ceilings Full ceiling vessels often lack ventilation
between frames therefore making them a likely place where decay can be found
Some vessels will be found with poured concrete ballast ingots or other interferences which make
internal bilge inspection and condition of floor and keel bolts difficult to
evaluate Where it is possible to remove some of the material without damaging the hull or
internal structural members sufficient access should be made for examination Careful
documentation of conditions found must be accomplished to avoid unnecessary removal of
The vessels underwater body should not be filled faired or painted before it is examined
Coatings cover a multitude of defects such as cracks bleeding or loose fastenings discolored
wood due to rot and borer attack
An overall examination of the hull of a wooden vessel which has been in service can give the
inspector an idea of the portions where deficiencies can be expected Distorted planking pulled
butts local damage and unexplained wetness or weeping are tell tale Particular attention should be paid to the garboard area stem stern transom
region under the
covering boards the wind and water area and around hull fittings It is impossible to list each
area of trouble in each type of boat In general areas which are hard to maintain have poor
ventilation or are subject to heavy stresses display the most INSPECTION FOR DECAY AND WOOD BORERS
Serious deterioration of a wooden hull goes on within the wood itself with little or no outward
sign until it is well advanced In order to spot decayed wood which has not progressed to the
point where the wood appears eroded and spongy sounding with hammer can be of use
Unsound wood will give a dead or dull sound Heavy timbers whose interiors are rotted may give
a distinctive drumlike tone where the sound is not that of good solid wood the member is
suspect Often the first indication of wet rot is a distinctive musty odor which permeates the
interior spaces of a closed up vessel Deteriorated wood will be spongy when probed and repairs
generally require complete renewal of the affected wood
1 Decay Decay in wood is caused by various fungi which are living organisms whose growth
depends upon suitable temperature 50 degrees to 90 degrees F suitable food wood
moisture and oxygen Wood that is dry will not rot nor will waterlogged wood In order to
provide a condition suitable for fungus growth wood must be moist from 20 to 80 moisture
content This condition is promoted by poor ventilation A well designed vessel should have
adequate ventilation of its enclosed spaces Bilges cabins etc of vessels in service should be
opened periodically to allow a change of air Good ventilation of interior structure in wooden
hulls is one of the most effective measures in the prevention of decay
It should be realized that decay progresses rapidly and that it is more economical to eliminate
small decayed areas early than become involved in costly major replacements caused by
neglected decay
Moisture meters can be of use particularly in areas where FRP overlays or paint may hide
deteriorated wood Use of the moisture meter andor hammer should be followed up with
probing or boring to develop the extent of the defect Core sampling can be used to determine
depth of It is imperative that probing and boring be avoided Holes made by a probe or
drill on the exterior are potential entry ways for wood borers In the hull interior they allow
moisture penetration and thus aid in starting decay Probing and boring should be done
carefully and only where there is an indication from testing that the material is
unsound not as a matter of routine
Holes made by boring should be plugged with dowels or plugs which are glued in place not
merely driven into the wood Plugs and dowels should preferably be treated with wood
preservative to prevent future trouble Areas which have been probed should be filled with a
suitable compound When covering boards or other obscuring construction is involved it is
often difficult to locate deteriorated members by probing In such cases when bolted or
screwed fastenings are used check for tightness of randomly selected fastenings If the
member is solid the fastenings thus set up will take hold at the beginning of the turn If serious
decay is present the fastening will turn freely and fail to take a bite indicating soft and spongy
Decay is most often found in the following Internally
1 All areas that are poorly ventilated ie at the stem transom and along the sheer
2 In the bilge especially at the turn and along the keel
3 The lower courses of bulkhead planking
4 Areas under freshwater tanks and valves and other areas where fresh
water can accumulate
5 In the area of butt blocks and longitudinal members where dirt and debris may have
retained fresh water
6 At the heads of frames caused by fresh water leakage through defective covering
boards and from 7 Where the futtocks of sawn frames join and at the faying surfaces where the frames
abutt the hull planking
8 At the terminal ends of frames floors engine foundations etc where end grain is
B Externally
1 In joints where fresh water has penetrated
2 Around deck metallic fastenings and 3 At covering board joints
4 In mast fastening locations and within natural checks or compression crac ks
5 Under spar hoops gaff jaws mast partner deck penetrations and any other areas
where wood is covered with metal or leather chafing gear
Under freezing temperature conditions wood structural members with a high moisture in the bilge areas may appear quite sound when in fact they may be
in of decay Periodic examination of these areas should be conducted before freezing sets
in or after allowing sufficient time for thawing
The other principal form of deterioration which goes on within the wood is wood borer attack
2 Marine Borers Marine borers are present to a varying degree in almost all the salt and
brackish waters of the world They attack practically every species of wood used in boat
construction There is no sure method of protection from their attack The two principal
methods are to physically keep the worm away from the wood sheathing and to make the
wood unattractive to the worm toxic substances and coatings The main types of marine
borers are listed in the following paragraphs
A Mollusks Often called shipworms There are several species of Teredo and Bankia in this
group Though they vary in detail their attack upon wood follows the same pattern
They start their lives as tiny free swimmers Upon finding a suitable home even a tiny
crack in a sheathed bottom they attach themselves and quickly change form As a pair of
cutting shells develop on their heads they bury themselves in the wood and feed upon it
Their tails or syphons always remain at the entrance to their burrow but as the worms
grow their heads eat channels in the wood The entrance holes always remain small and
hardly noticeable but the interior of the wood becomes honeycombed When they are not
crowded some species of shipworm can grow to lengths exceeding four feet One species
Teredo Navalis can burrow up to 34 per day
B Martesia These are wood boring mollusks which resemble small clams they enter the
wood when they are small and do their damage within They do not grow to the length of
shipworms but nevertheless they can do considerable damage Their main area is in the
Gulf of Mexico
When borer attack is just starting it is possible to burn the holes clean with a torch and then
fill them with a suitable compound If the attack is extensive however the only method
acceptable is to replace the affected wood
The first principle in reducing the chance of borer attack is to keep the worm away from
the wood This is accomplished by sheathing or by toxic paints If the protective coating is
broken borers can enter To prevent this sheathing where fitted should be unbroken and
in good condition and the bottom paint should be free from scratches nicks and scrapes
before the vessel is launched
Wormshoes rubbing strakes and similar members whose protective coatings have been
broken should be inspected carefully If they have heavy borer infestation they should be
replaced Care should be taken to see that the infestation has not progressed from them to
the main part of the hull structure Though wormshoes are usually separated from the hull
by felt or copper sheathing this separation is never 100 45
Marine borers die when removed from salt water for any period of time A vessel which
has been out of the water for a few days and is essentially dry will probably have no live
3 Termites Classified as a wood boring worm found principally in tropical areas the winged
variety often infest masts and wood appendages of large sailing craft particularly those with
solid grown spars which have developed surface checks or compression cracks
Termites burrow deep into the wood leaving tunnels which fill with water and promote decay
Hammer testing and use of the moisture meter can often detect subsurface termite colonies If
borer infestation is suspected under canvas deck coverings or in areas where wood is covered
or sheathed with metal leather or composite overlayment the covering should be removed to
1 General Most wooden boats relay on metal fastenings for structural integrity and those
fastenings are subject to corrosion Because of the great structural importance of the relatively
small mass of metal in the fastenings a small amount of corrosion can cause major problems
therefore the inspection of fastenings is crucial Many casualties to wooden vessels involving
structural failures are caused by corrosion of the fastenings Underwater metal fittings of
wooden vessels but usually not individual fastenings are often protected electrically from
corrosion by a process called cathodic protection Wood in contact with cathodically protected
fittings is often deteriorated by the chemicals produced by the protection process
In inspecting fastenings several fundamental facts must be kept in mind First most corrosion
of metal fastenings in wood proceeds from the surface to the interior at a fairly constant rate
which can be predicted quite accurately by experience if the metal the temperature and the
nature of the surrounding wood are known
Second when a fastening is loaded in shear like many bolts are its strength is related to its
area Because the area varies as a function of the diameter a fastening which is
corroded to onehalf its original diameter retains only onequarter of its original shear strength
Third fastenings which are loaded in withdrawal tensile rather than in shear and which rely on
threads or friction for their holding power such as screws lags nails and drifts may lose their
effectiveness completely when only a small fraction of their original diameter is lost to
The metals used for hull fastenings in wood boats are steel often coated with zinc or
galvanized to increase corrosion resistance bronzes alloys of copper with metals other than
zinc copper nickelcopper Monel stainless steels alloys of iron with chromium and nickel
and occasionally 46
Fastenings can suffer from four principal classes of corrosion simple corrosion galvanic corrosion replacement corrosion and stray current
corrosion Stainless
steel fastenings are also susceptible to a form of corrosion called crevice Simple Corrosion Simple corrosion is the normal way in
which metals combine with oxygen to reach their more stable form as metallic oxides In sea
water dissolved oxygen and chloride ions from salt are the principal instigators Simple
corrosion rates are quite predictable for most metals The process involves
two different types of reactions which take place at distinct locations on the metalwater
interface An interface of metal and wet wood is the same as an interface of metal and water
At the anodes the free electrons are absorbed in a reaction that consumes the oxygen which is
dissolved in the surrounding water or in the water absorbed by the surrounding wood In
open water the sites of the anodes and the cathodes may be small and
intermixed the metal may appear to corrode more or less uniformly For a fastening buried
in wood however the area exposed to oxygen is often limited The heads of fastenings tend
to support oxygen consuming cathode reactions and are thus protected from wastage while
the deeperburied shanks are where the anode reaction and the physical wastage takes place
For this reason exposed or shallow buried heads are often the parts of hull
fastenings This is why hull fasten ings in wooden boats cannot usually be adequately
assessed without withdrawing them
3 Galvanic Corrosion Different metals have different levels of chemical stability in water
causing them to have different tendencies These differences in stability are measurable as
different electrical potentials or voltages These potentials are tabulated in the Galvanic
Series See Table 41 on page 417 at the end of this chapter
When two metals which have different potentials and which are immersed in the same body of
water or wet wood are brought into direct physical contact or connected together with a
metallic conductor electric current flows between them altering their corrosion rates from
those which existed in the isolated state The corrosion rate of the less stable metal which had
the more negative potential increases while that of the more stable metal which had the more
positive potential before the connection was made decreases by an equal amount The less
stable metal is now said to be undergoing galvanic corrosion an accelerated form of
corrosion while the more stable metal is now receiving cathodic protection
with the other metal serving as a sacrificial anode In order for galvanic corrosion to occur the
two different metals dissimilar metals must be connected electrically by contact or by a direct
metallic link and they must be immersed in the same body of liquid or wet wood either of
which is called an electrolyte Two or more metals electrically connected in a common body
of electrolyte are called a galvanic cell
Galvanized steel steel coated with zinc is an example of an intentional galvanic cell the zinc
acts as a sacrificial anode for the steel in the case of a small penetration of the coating In
addition despite being less stable than steel galvanically the zinc is considerably more
corrosion resistant than the steel when its not acting as a sacrificial anode for a large area of
steel Theres a lesson here the Galvanic Series should be used only to predict the nature of
galvanic interactions between metals not to predict their relative corrosion rates For
example aluminum which is also less stable galvanically than steel also has a lower corrosion
rate than steel if it is galvanically isolated
The ratio of the exposed areas of the two metals which make up a galvanic cell is an important
factor in what happens to the metals In the case of a cell made up of a small piece of copper a
stable metal and a large piece of steel an unstable metal the corrosion rate of the steel would
be only slightly increased by the connection while the copper might be completely protected
from corrosion If the area ratio were reversed a large area of copper to a small area of steel
the corrosion rate of the steel already high would be greatly increased while the corrosion
rate of the copper already low would be decreased only slightly In the first case if the
copper is in contact with wood the cathodic protection it receives comes at a price The
increased conversion of oxygen to hydroxyl ions which accompanies the protection will cause
deterioration of surrounding wood Regardless of the area ratio painting the copper will
decrease not only the adverse affect on the wood but the detrimental galvanic effect on the
steel as well Painting the steel may decrease the total galvanic effect but will concentrate
what there is at small imperfections in the paint film causing severe localized pitting which
could be disastrous to thin material found in fuel or water tanks
In general galvanic connections should be avoided in wooden vessels unless they are made for
a very good reason like cathodic protection and the consequences like wood damage around
protected metals have been fully considered and mitigated such as by painting the protected
4 Replacement Corrosion If a metal fitting or fastening is placed in an electrolyte which contains
ions of a more stable metal typically a galvanized steel or stainless steel fitting in pressure
treated wood containing copper salts the copper ions coming into contact with the fastening
will plate out as a solid copper film on the surface of the fastening with equal numbers of
zinc or iron atoms ionizing or going into solution The replacement reaction itself is a onefor
one process and if the stable copper ions are depleted from the electrolyte the replacement
stops However the thin surface coating of copper on the steel fastening results in a galvanic
cell which accelerates the fastening corrosion rate
The three principal causes of replacement corrosion to wooden boat fastenings are in
descending order of frequency and the likelihood of significant damage
A Copper wood preservative salts These include copper napthenate from green Cuprinol
which is usually brushed on and chromated copper arsenate CCA and ammoniacal
copper arsenate ACA which are used in pressure treating softwood lumber
B Copper salts dissolved in bilgewater Copper chloride is occasionally used as a cure for
the sour bilges hydrogen sulfide caused by bacterial decomposition of spilled diesel and
lube oils
C Nearby copperalloy fittings or fastenings After a long period of time wood around
corroding copper alloy fittings or fastenings becomes saturated with copper ions Any
steel galvanized steel or stainless steel fastening driven into that area can suffer some
replacement and consequent accelerated corrosion from galvanic effects The effect only
extends for a few inches at most around the copper alloy fitting however its prudent not
to use galvanized or stainless steel fastenings for refastening boats previously fastened with
copper alloy fastenings whether or not the original fastenings are removed
5 StrayCurrent Corrosion Straycurrent corrosion is a magnified version of the galvanic
corrosion suffered by the more negative metal in a galvanic cell In the galvanic cell the metal
is connected to another more positive metal which draws electrons from it and causes the
anode reaction rate of the negative metal to increase to supply those extra electrons In stray
current corrosion a metal comes into contact with the positive side of a DC electrical system
the negative side of which is grounded to the seawater The effect is the same but since the
driving voltage is now 12 volts or more instead of the few tenths of a volt found in galvanic
cells the resulting corrosion rate can be Typical sources of stray current are submersible bilge pumps bilge pump float switches and
electrical wiring connections in the bilge area which might become submerged in the
bilgewater Fittings can be subject to stray current corrosion by coming into direct contact
with a chafed positive hot DC wire or more commonly indirectly by a DC fault current to
the bilgewater Fittings which pass through the hull and are in contact with the outside
seawater are most susceptible In the case of an indirect stray current path through the
bilgewater fittings which are in direct contact with both the bilgewater and the outside
seawater are most Figure C Stray Current 49
Stray current corrosion generally causes deep pitting of the objects it affects and is almost
always highly localized to within a few feet of the source of the stray current In addition the
effected metal parts will appear to be unusually bright or shiny A DC stray current may cause
complete of a substantial fitting within a few days or even less The magnitude
of the DC stray current may be a few amps in severe cases but usually not high enough to
cause overcurrent protective devices to trip Stray current can discharge batteries quickly but
in boats with shorepowered battery chargers a substantial DC stray current may continue to
In order to protect against the potentially disastrous effects of DC stray currents many non
metallic hulled boats have a network of wires which connect hull fittings which are at risk of stray
current corrosion with the negative or ground side of the battery usually via the engine
block This network is called a bonding system In the case of a direct fault to a bonded fitting
sufficient current will probably flow to trip the overcurrent protective device stopping the stray
current In the case of an indirect stray current the wire in the bilgewater it is unlikely that a
sufficient current will flow to trip the circuit even with a bonding system In this case the bonding
system and the stray current will share the fault current An indirect fault however is often
limited by the corrosion of the exposed metal at the source of the fault which eventually stifles the
current flow
Figure D Bonding Systems
Hot wire
touches fitting
The bonding system ties the thruhulls electrically to the negative terminal of the battery When
a hot wire touches the thruhull the electrical path presented by the bonding wire has so much
less resistance than the electrolytic path of the straycurrent cell that a high current flows in the
bonding system This should cause a fuse to blow or a circuit breaker to trip interrupting the
stray current flow Even if this does not happen however the amount of current that flows in the
straycurrent circuit before the battery becomes discharged and the resulting corrosion of the
affected fitting are greatly diminished
When there are no stray currents the shaft zinc may protect not only the shaft and prop but also
any fitting connected to the bonding system This often results in alkali damage to the wood
around those fittings
On wooden boats bonding systems can cause unexpected problems First by connecting
together a number of underwater fittings and fastenings the bonding system may provide the
metallic links which turn otherwise isolated dissimilar metals into a galvanic cell Second the
bonding system often inadvertently supplies unneeded or unwanted cathodic protection to objects
connected to the bonding system by connecting those objects to the propeller shafts sacrificial
zinc anode This cathodic protection of underwater metal hull fittings often causes damaging
alkali of the surrounding wood
The fittings on a wood boat which are most susceptible to straycurrent corrosion are those in the
bilgewater or those which are in close physical proximity to wires while those most susceptible to
alkali are those above the bilgewater level but below the waterline In this area the
wood is wet enough to be a fairly good electrolyte but there is little flushing action to remove
accumulations of cathode reaction products The hydroxyl ions produced by the cathode reaction
on cathodically protected metals can concentrate in these locations damaging the wood and often
producing visible deposits of sodium hydroxide lye crystals which appear as a white mound of
salt around fastenings
Bonded vessels should be checked with a electrical potentiometer by a qualified electrical
specialist for electrical leakage to ensure that the boat is not over zinced This is especially true
after a vessel has been found to have extensive wood repair due to alkali Repairing
the wood without determining the cause via a corrosion survey is a poor practice as it would
only be treating the symptom
Care must be taken in painting metals which are connected galvanically to other metals In the case
of steel and copperalloy fittings it would seem to make sense to worry more about the coating of
the steel since it is more prone to corrosion than the copper alloy If however those fittings are
connected together forming a galvanic cell painting the steel but not the copper may result in a
tremendously unfavorable area ratio for a few spots on the steel that are inadvertently not coated
well When painting galvanic cells one should always try to make the area ratio more favorable to
the susceptible metal The answer is to paint both metals and to pay particular attention to
reducing the exposed area of the cathode of the cell the copper
Stainless steels are subject to a particular type of corrosion called crevice corrosion which is a
severe form of pitting Crevice corrosion can destroy a fastening in a few years while only
damaging a small fraction of the total mass of the fastening The austenitic stainless steels
including the most commonly encountered types 304 and 316 derive their corrosion resistance
from a surface oxide film which is in air or in the presence of oxygen dissolved in an
electrolyte In stagnant areas like wet wood or underneath marine growth or paint however
oxygen can be depleted by cathodic activity allowing the everpresent chloride ions to destroy the
film in small areas which then undergo unpredictable and exceedingly rapid corrosion
wet wood is a nearly perfect environment for crevice corrosion Stainless steel must
be used with great caution as a fastening material for wooden boats and inspectors should be
suspicious of all stainless steel fastenings especially wood screws used on boats in saltwater
service Type 316 contains more nickel and chromium than type 304 and it also contains
molybdenum which inhibits crevice corrosion to a certain extent but it is not completely immune
Barbed or ring nails of type 316 are available but wood screws of type 316 are generally not
A boat is no better than its fastenings The most common type of fastenings found on wooden
boats are screws however certain types of construction utilize nails bolts or rivets Most hull
fastenings are concealed from view being countersunk and covered therefore their inspection is
Regardless of the type of fastenings involved inspection to ascertain condition is necessary in
most plank on frame boats
For purposes of uniformity careful fastening inspection must be carried out on all vessels
Removal of fastenings should be conducted as follows
1 For Cause Saltwater And Freshwater Service Remove fastenings whenever inspection
reveals the probability of defects such as when a plank or planks are proud and have moved
away from the frames or indications of loose bungs rust bleeding from fastening holes etc are
Particular attention should be given to exposed hull fittings and through bolts accessible inside
the hull such as keel bolts chine bolts and double frame clamp and floor timber bolts These
are as important to the total hull structure as plank fastenings They should be sounded with a
hammer or wrench tightened and if suspect some should be pulled for inspection Often a bolt
will be completely wasted away in the middle at the faying surface of the joint and will break
and come out when pried up This is caused by moisture accumulation which besides wasting
the fastenings forms an excellent place for wood decay to start
2 Periodic Inspection of fastenings can prevent failure Random sampling of
fasteners should be part of a regular maintenance program for continuously monitoring the
structural condition of the vessel Therefore for vessels designed and built to Subchapter T
Inspection Standards random sampling of fastenings should begin at the 10th year of age and
every 5th year thereafter in salt water service and 20th year of age and every 10th year
thereafter in fresh water service
For existing vessels not originally built to Subchapter T Inspection Standards but certificated
later in life random sampling should begin at the 5th year of age and every 5th year thereafter
in salt water service and 10th year of age and every 10th year thereafter in fresh water
Scope Of Periodic Random Sampling Of Fastenings
a Remove a minimum of eight fastenings per side below the waterline
b Concentrate sampling in the following areas
Garboard seams
Stem joints
Plank ends in areas of bent planks
Shaft logs
Under engine beds where vibration is maximum
c In vessels of cross plank CHESAPEAKE BAY DEADRISE construction specifically
inspect fastenings at the keel and chine joints at transom attachments and over the
It is extremely important that the type material and location of the fastenings removed along
with a description of their condition be accurately documented This includes areas of the
vessel which have undergone refastening as well Use of a camera is invaluable in recording
areas of interest during Composite cold molded and laminar builtup wooden hulls often depend on adhesives and
resins for fastening purposes Inspection of these type vessels requires common sense and
good judgement to identify the method of construction used and thereby determine the extent
of inspection required Generally these vessels do not require periodic random sampling of
fastenings by removal except for cause
The art of caulking is an ancient one which requires experience and a certain touch A good
caulker makes his work look easy but it is a skill which takes much experience to develop
Caulking materials are subject to It is advisable to search the seams in any doubtful
areas and recaulk Caulking should be uniform and well horsed home This can be checked
with a probe or knife Care should be taken that the caulking has not been driven clear through the
seam Over caulking is as bad as under caulking
Extensive trouble with caulking may be indicative of structural problems which often includes
broken or deteriorated fastenings andor frames If a hull works excessively caulking may be
squeezed out In such cases the hull structure will have to be made sound before caulking will
In old hulls where the seams have become enlarged from repeated recaulking copper or lead
strips may have been nailed over the seams to act as caulking retainers These are a temporary
remedy and are an indication of poor general condition of the vessel It is advisable that such strips
be removed and the seams inspected for excessive width poor caulking and decay In some cases
wide seams can be repaired by the use of thin wedge shaped splines driven into the wide seams and
bedded in marine adhesive This procedure requires excellent workmanship and should be pursued
with caution In most cases where garboard seams have widened beyond caulking limits
refastening of the keel frames and renewal of the garboard planks may be the only acceptable
methods of repair
Rudder and propeller struts and fastenings should be examined carefully If suspect random
removal of fastenings for inspection should be accomplished The steering arrangement should be
inspected from the steering wheel to the heel pintle Wear in the carrier bearing and excessive
clearances elsewhere should be corrected Tiller lines should be in good condition with shackles
moused and bolts cottered
The shaft log glands should be in good condition and the deadwood should be sound This is often
neglected and is a potential cause of leakage
Propeller shaft cracks are sometimes found at the keyway A careful examination here is essential
Magnetic particle testing is usually not available in a small boatyard so the inspector must depend
on visually locating surface cracks Dye penetrant testing is relatively inexpensive and can be useful
when deemed necessary
Some older boats are still fitted with AM radio hull grounding plates These are usually copper
sheet metal of several square feet in area attached to the underwater hull Use of AM radio
equipment is no longer found on small passenger vessels To minimize the mixing of metals below
the waterline the old ground plates should be removed and the hull inspected repaired as found
necessary and 414
Inspection of hardware fastenings should also be accomplished including cleats bitts chain plates
etc where threaded fasteners hold load bearing as well as structural parts
Most hull damage can be seen readily Cracked and broken members are obvious faults
Likely locations for cracks or breaks are in areas of high stress or where the structure undergoes a
sudden change in shape The turn of the bilge is the prime location for breaks of this type The
harder the turn the more chance that damage has been done Bent frames are particularly
susceptible to breakage under bilge stringers especially when the stringers are substantially thicker
than the planking or when there are large diameter fastenings in the stringers
Wood hulls are more prone to secondary damage remote from the site of collision or grounding
than are steel hulls Damage may consist of sprung butts pulled fastenings sprung or cracked
frames and misalignment of the structure In inspecting any damaged wooden hull the entire
vessel should be checked
O When deficiencies are encountered an evaluation must be made of their extent and their effect on
The following factors must be weighed in making this 1 Is the defect progressive and if so how can its progress be arrested
2 How long will it be before the area in question is next inspected
3 Is the work contemplated necessary to restore seawo rthiness or to prevent the vessel from
becoming unseaworthy or is it a maintenance measure to prolong the life of the vessel
Specific requirements detailing the nature and extent of required repairs should be written
However with wooden vessels the general rule renew as original while applicable is not always
practical nor necessarily the best way to effect repairs Most accepted methods of marine repair
may be used as long as the vessels strength is not adversely affected
Wood is a natural material its quality cannot be controlled as closely as with a manmade product
such as steel Consequently the inspector should check the material to be used in repair work
Special attention must be given to the type of wood proposed for each purpose and for any
inherent defects
Many deficiencies particularly surface defects or scars caused by chafing freezing and other forms
of exterior deterioration are not as serious as they may first appear Do not be hasty in requiring
the correction of minor defects of this nature in otherwise sound seasoned planking
For Adequate Repairs Are
1 Use of good material comparable in properties to that replaced
2 Repairs extensive enough to ensure that the hull is at as strong as the original
3 Construction details and fastenings at least equivalent in strength and in quality to
those replaced
4 Good 416
TABLE 41 THE GALVANIC SERIES OF METALS IN are those measured against a silversilver chloride AgAgC1 reference electrode
Noble or Cathodic Metals Designation Potential
Graphite C 027 V
Platinum Pt 024 V
Titanium Ti 002 V
Incoloy 825 002 V
AgAgCl Reference Electrode 000 V
316 Stainless Steel passive 003 V
Monel 70 30 cu 400K500 006 V
304 Stainless Steel passive 006 V
Silver Ag 010 V
Nickel Ni 013 V
Silver Brazing Alloys 013 V
Inconel 600passive 013 V
NiAl Bronze C63xC9548 016 V
CuNi 7030 C7159 C964 018 V
Lead Pb 020 V
CuNi 8020 and 9010 C710 C706 022 V
Nickel Silver C74570 C97x 025 V
Phosphor Tin Bronze C524 C9035 C92x 026 V
Silicon Bronze C655 C872 025 V
Manganese Bronze C675 C86x 029 V
Admiralty Brass C4435 030 V
Aluminum Brass C68790 030 V
LeadTin solder 030 V
Copper C10x Cllx C12x 031 V
Tin Sn 031 V
Naval Tobin Bronze C464 033 V
Yellow and Red Brass C23x27x C83x85x 033 V
Aluminum Bronze C60624 C9523 034 V
Stainless Steel 316 active 039 V
Stainless Steel 304 active 049 V
Low Alloy Steels 058 V
Steel Cast Iron 063 V
Aluminum Alloys 08710 V
Zinc Zn 100 V
Magnesium Mg 160 V
Notes on the Use of the Galvanic Series Table
All values are for sea water at room variability is 04 Volts for alloys containing nickel or iron 02 V for copper nickel
Sign of corrosion potential assumes that the COMMON or negative Black terminal of the
voltmeter is connected to the reference electrode and the VOLTSOHMS or positive Red terminal
is connected to the metal to be measured The reference electrode must be immersed in the same body
of electrolyte as the metal being measured preferably in close use Zinc as a reference electrode instead of AgAgCl add 100 volts to the potentials
listed in this
table For example low alloy steel should measure 58V 100 V or 042V against zinc and
magnesium should measure 160V 100Vor 060V against zinc Extremely should not be attempted with zinc as a reference since it isnt as stable as the
are receiving cathodic protection when their measured potentials are more negative than their
natural corrosion potentials listed here and are generally completely protected from corrosion when
their potentials measure 20V to 25V more negative than the values listed in this are receiving stray current or are the anode of a galvanic system
these are equivalent their potentials measure more positive than the values listed in this chart Metals in this situation
are generally suffering accelerated alloy designations Alloys numbered C100 to C799 are wrought alloys those numbered C800
to C999 are casting alloys x indicates a range of alloys sharing the preceding digits
Wood boat construction varies widely from locality to locality and boat to boat All types of
repairs which an inspector may encounter cannot be listed types and standards
which are given here are intended as a general guide to good practice and as an aid in evaluating
required repairs Repair standards for wooden hulls should be developed for each locality on
the basis of prevailing conditions and practice
When planking is replaced the frames and other structures should be thoroughly inspected and
placed in good condition Holes made by old screw fastenings should be properly reamed clean
and may have the cavities filled with an epoxy mixture thickened so as to provide a filler which
will hold fastenings like wood Since nail fastenings depend upon the swelling of the wood
around them after they are driven for their holding power this technique should not be used for
holes made by old nail fastenings Holes made by old nail fastenings should be properly reamed
clean and filled with dowels set in a suitable adhesive
When fastenings are loose it does little permanent good to harden up those which exist
Additional fastenings properly placed are the preferred repair where there is sufficient room to
obtain good holding power without seriously weakening the planking or frames If there is not
room holes in the substructure from the old fastenings may be repaired as noted above and
new slightly oversized fastenings may be driven Loose planking can also result from
deteriorated frames and other substructure in which case refastening is useless unless the
structure is first made sound
Replacement fastenings should be at least equal in size number and of the same material as
those of the rest of the planking
Mixing fastening materials invites galvanic corrosion and should be avoided Use of stainless
steel fastenings in underwater body salt water plank fastenings can result in early fastening
failure due to crevice corrosion and should also be avoided See Page 412 for details on
crevice corrosion
As a rule of thumb the replacement plank should extend at least six frame spaces and no portion
of a plank shorter than six frame spaces should be allowed to remain Where special conditions
govern this rule may be modified but as a lower limit the replacement plank should be at least
5 feet long and its butts should be spaced in accordance with the rule for butts in this chapter
When hull planking is placed on a boat it should have the concave side of the annual rings
facing toward the frame This prevents cupping as the moisture content of the wood changes
Deck planking which generally sees drier service should be placed with the grain on edge or
vertical If slash grained planks are used especially when the planking stock is not fully dried
and the boat is painted a dark color it is entirely possible that the planks will dry out in service
and the edges of planks whose ring curvature is inward will lift Some builders based on the
moisture content of the planking and the expected service conditions will intentionally place the
concave ring curvature outward in the topsides This is good boat building practice and it
should not be is sometimes necessary to shape the inboard side of a replacement plank to fit tightly against
the frames The use of shims or packing pieces for this purpose should not ordinarily dutchmen or short lengths of planking are normally not
acceptable since they will not
hold fastenings and are structurally unsound
The same principles apply to diagonal planking but due to the relatively short lengths of planks a portion of a plank is seldom the proper repair of
double and triple diagonal planking is expensive and short cuts involving the use of dutchmen and backing blocks are These should not be permitted
Most other planking systems follow the same of repair as outlined here Good workmanship and care are the major proper repair See Wooden Boat
Restoration and Repair Reference 6
D PLYWOOD surface defects may be repaired using commercial fillers epoxy putty etc In allowing
this type of repair the wood must be decay free and all damaged wood removed Minor repairs
of this type are satisfactory where basic strength has not been affected The danger lies in
covering up progressive defects such as decay which grow worse under the repair areas up to a foot square can be successfully repaired by cutting the
damaged area
away in a rectangular or oval shape installing a backing block of equal thickness as the and shaping an insert piece to suit the cutout The repairs
should be set in place with
marine adhesives ie Resorcinol glue or epoxy and fastened with wood screws Filling fairing
and coating complete the repair
Large panel damages should be evaluated to determine if a beveled insert section can be used
for the repair or if the entire panel must be replaced
Each plywood repair must be evaluated as to cause location materials and strength achieved
through the method selected For detailed repair methods refer to Wooden Boat Restoration
and Repair Reference 6
Planking butts should not terminate on frames in normal construction They should be located
between frames on proper butt blocks though in light construction with narrow strakes they
may sometimes be found as glued scarf joints at the frames and in some construction with
massive framing they may be found butted on the frames As a rule of thumb butts in adjacent
planks should be at least three frame spaces apart for transversely framed planked
Those butts which fall in the same frame bay should be separated by at least three solid strakes
This is not always possible especially at the end of the vessel but serves to illustrate the
principle of keeping butts separated as much as possible Where frame spacing is unusual the
following rule may be used as a guide
Butts in adjacent strakes should be no closer together than 5 feet If there is a solid strake
between they should be no closer than 4 feet Butts should be shifted so that three or more do
not fall on a diagonal line
To be effective a butt block must have adequate size See page C12 If the frame spacing
allows its length should be at least 12 times the planking thickness Its thickness should be one
to one and a half times the planking thickness and its width at least 1 greater than the strake
width Prior to installation it is recommended that the faying surface of the butt block and
strakes be coated with a wood preservative The top of the butt block should be curved or
chamfered to allow for water run off Avoid butting the block hard against the frames to
minimize decay
The fastenings of the strake to the butt block should be of equal strength to that of original
butts The fastening size should be equal or larger and no fewer number of fastenings should be
allowed Through bolts or machine screws are preferred fastenings in butt blocks because the
joint will achieve maximum strength Care should be exercised to avoid over tightening so as
not to crush the planking or split the butt block
Plywood butt blocks should be avoided because plywood has somewhat less strength than the
along the grain strength of the basic wood from which it is made Plywood is also prone to
delamination and rot 53
For new construction or for repairs not in kind the following table lists the suggested number
of fastenings for planking
Suggested Minimum number of fastenings for planking to butts and frames
Number of Number of Fastenings in Frame
Width of Fastenings 12l Inch ll 12 Inch 1 122 Inch
Plank in Butt of Plank Plank Plank
inches Each Plank Thickness Thickness Thickness
34 3 2 2 2
46 4 2 2 2
67 5 3 2 2
78 5 3 3 2
810 6 3 3 3
Glued Scarf Joints
For a glued scarf joint the plain scarf without nibs see Figure E is the simplest and strongest
Water resistant glue or epoxy resin should be used and the slope of the joint should be 112 or
flatter for maximum joint efficiency
Scarf Slope Typical Joint Efficiency for a well
made glued joint without nibs
112 90
110 85
18 80
15 65
These efficiencies can be attained only with optimum adhesive conditions and excellent
Mechanically fastened scarf joints are most often nibbed hooked or keyed to provide extra
axial restraint and to aid water tightness
The surface of scarf joints should be smooth and flat to ensure good fit and adhesion
Fastenings should be adequate in size and number and arranged so as to prevent splitting the
There is considerable advantage in the use of splitring timber connectors in joints including backbone scarf joints Timber connectors should be the
futtocks of full double sawn or alternating double sawn frames which are in line
with heavy of inside or outside mechanically fastened scarf joints are nibbed at the ends for a depth of approximately 15
of the depth of the member giving a joint length of at least 6 times the depth
A scarf joint which is fastened by mechanical means alone cannot even under the best produce a joint approaching a solid member in Butt Joints
Glued butt joints never give joint efficiencies of over 20 and should not be permitted Refer to
Figure E Common Forms of Scarfs
Sister Frames
Damage to frames can be repaired by the use of sister frames though it is preferred that the
frame be replaced if The preferred type of sister frame is one of equal size to the damaged one and as long as
possible They should extend at least 18 or approximately four plank widths beyond the
damaged area This frame should be fastened to the planking and other structure with fastenings
at least equal in size and number to those of the damaged member
Care should be taken when recommending that sister frames be of greater size than the damaged
frame they reinforce The weakening effect of bending is inversely proportional to the square of
the bend ratio see Bent Frames Wooden Boat No 86 page 87 This means that using a
sister frame which is deeper larger in molded dimension than the original frame will produce a
more severe bend ratio in the sister frame and may actually result in the sister frames being
weaker than the original frames despite being larger Often the original frames broke because
their bend ratio was too severe in the first place Successful sister frames may be kerfed if
necessary to ease the severity of the bend when that was the problem with the original frames
This greatly increases the effective tensile strength of the sisters without any necessity for
greater It is important to note that bending sister frames into hard spots in the hull caused by broken
frames may cause locally severe bends in the sisters which will very likely cause them to break
in service If the hard spot cannot be corrected this usually requires removal of the original
frames it is actually better to let the sister frame bend fair spanning the hard spot and then to
shim it to the planking rather than bending it into the hard spot
Long sister frames well tied in to the main structure of the vessel should not normally butt
against damaged frames though this is acceptable where it forms the best method of tying in the
new frame If the frames abutt a good bedding compound or adhesive is required to exclude
moisture from between the pieces
Where structural or machinery interference or other reasons prevent fitting a long sister frame
well tied into the other structure a shorter partial sister may be fitted as a temporary repair
This should extend as far as practical on both sides of the damage and should be securely
fastened to the damaged frame by bolting or equivalent means as well as to the planking and
other structure Provisions should be made to exclude moisture from between the pieces
Temporary repairs of this nature should be monitored closely followed by evaluation for
consideration of further repairs or acceptance as permanent repair Unusual or nonstandard
repairs accepted as permanent should be properly documented in the vessels permanent file
A good wood preservative is recommended for use on all faying surfaces Ensure that
precautions are taken that water cannot accumulate at the top of the partial frame and initiate
decay A sister frame should not be used as a repair for decayed frames The decayed wood
will eventually seed the sound wood with decay spores in spite of any attempts to prevent it
by the use of wood preservatives or to isolate the new wood with sealing compounds When
extensive decay is present in a frame the only permanent repair is to replace it and any adjacent
wood affected If the decay is localized or such that frame replacement is not practical the
decayed section of frame may be cropped out and replaced with a new section using a
maximum scarf angle suitable adhesive and by mechanically fastening the new scarf joint A
sister frame of the appropriate dimensions may then be placed next to and centered around the
new scarf joint in the original frame This repair may be considered permanent after proper
monitoring and evaluation as previously described
Where frame damage is evident but sister framing is not practical consideration can be given to
installing interframes between the affected frames or to strengthening damaged or weakened
frame areas with fitted metal frames Such repairs require excellent design and
workmanship and should be undertaken with caution
Heads of frames under covering boards often become decayed due to lack of ventilation and
accumulation of fresh water leakage With sawn frames this can be corrected by replacing the
upper futtock If the futtock is long or the frame is in one piece it can often be cropped off well
below the rot at least 2 feet is a good rule and a piece spliced in using a glued and screwed
scarf joint of proper dimensions As an alternate measure a lap joint of sufficient length may
replace the scarf Repairs to more than two adjacent damaged frame heads should not be made
by short cropping but should be made by renewing the frames or replacing the damaged sections
by scarfing and then sistering the frame
One of the principal causes of frame head decay is entry of water from deck leakage or
condensation into the exposed endgrain at the head of the frame This problem can be reduced
greatly by angle cutting the frame tops slightly short of the underside of the deck leaving a 18
to 14 space for ventilation and most importantly by painting the end grain of the frame heads
to prevent entry of moisture The slight gap between the frame heads and the deck also ensures
that if the sheer strakes should shrink slightly the covering boards margin planks will not be
lifted off the shear strakes by the frame heads
A method which can arrest the progress of incipient decay at least temporarily is as follows
The affected area is scraped clear of all decayed material and for some distance into
apparently clear sound wood A strong preservative solution for example l10
stock solution is applied freely This is allowed to soak in and dry
Repeated applications are made until the wood refuses to take any more Often a small cofferdam can be made to retain a pool of preservative
over the area To
be effective the preservative must sink in and sterilize the wood for a considerable distance
since decay sends out spores ahead of the damaged area
After the treatment is completed the cavity made by the scraping may be left unfilled but should
be painted Filling it will simply hide any additional rot still working
This method is a temporary repair only It will usually slow decay growth but will seldom
eliminate all traces of decay
Painting of wood structures not only prevents decay but also prevents rapid shortterm changes
of moisture content which result in structurally damaging dimensional changes The proper
coating of wood structures can be as important as coating of steel structures in maintaining
Although rejected by wood boat purists various reinforced resin systems have been tried with
some success both as new construction methods for cold molded wood construction and as a
method to restore strength and water tightness to existing constructed boats
Over the past 20 years several systems have proven themselves successful in service and have
been recognized by local OCMIs on a casebycase basis for certified small passenger vessels
The following guidance is provided to assist local offices in evaluating potential sheathing
Improper methods of reinforced resin overlay or overlay of an unsound structure will generally
not be long lasting This is especially true of sheathing vessels whose hulls tend
to flex or work The new laminate generally has little flexibility along its length and breadth
tending to age harden and develop tension cracks which destroy water tightness and strength
An evaluation should be made considering but not limited to the following items
1 In the hull even a hairline crack can allow undetected entry of marine borers
2 With old structure which has been painted or preserved a good bond is very difficult to
attain and will require mechanical fastening in addition to the adhesive strength of the
3 Any rot present will continue to grow worse under the sheathing if the proper
conditions of moisture and heat develop
4 It is difficult to acquire enough strength from a reinforced resin coating to make up that
lost from an unsound 5 It is difficult to check the soundness of the substructure once the sheathing system has
been applied
6 Boats which have been sheathed may be susceptible to interior deterioration from
inadequate ventilation Evidence of visible hog or sag along the keel or sheer lines
erratic moisture meter readings or areas soft to probing should be thoroughly
are three sheathing systems with which the Coast Guard is familiar and that have been
used on certificated small passenger vessels currently in service They each have of application which require varying degrees of hull preparation
These are
1 Vaitses Overlay This is a hull sheathing system developed by Alan Vaitses of
Mattapoisett which uses conventional polyester resin reinforced with a
layup of fiberglass matt and woven roving mechanically fastened with nails wood
screws or preferably heavy staples during the application After fastening is complete
several layers of matt are applied to complete the job This system was specifically
designed for overlay of existing vessels and has been successfully used for vessels from
yachts to heavy timbered commercial fishing vessels from 20 to 50 feet long A key
feature of the Vaitses Overlay system is that it requires minimum hull Details and specific guidance on hull preparation and proper
application of this method
are provided in Reference 15 Covering Wooden Boats with Fiberglass
2 WEST System Overlay This hull sheathing system developed by the Gougeon
Brothers of Bay City Michigan consists of overlays of plywood or cedar strips applied
diagonally to the hull and held in place with noncorrosive staples while fully saturated
in epoxy resin Proper wet out and control are essential to
achieve a good bond Sheathing should be conducted under cover protected from
direct sunlight and windweather Details and specific guidance on hull preparation and
the various methods of application of this method are provided in reference 5 The
Gougeon Brothers on Boat Construction and 6 Wooden Boat Restoration and
3 Fiberglass Planking System CFLEX The main component of this system utilizes
fiberglass rod reinforced high strength material and continuous fiberglass roving formed
into 12 wide planks This material is applied over wooden hulls perpendicular to the
plank line to withstand the of the wood planks and is securely
fastened to the planking with bronze staples A elastomeric
polyurethane adhesive designed for marine applications which will adhere to wet
wood treated wood and virtually all the various types of marine
planking woods is used to bond the material to the planking Being an elastomeric it
will withstand extreme stretch and compression forces without breaking its bond a
quality essential in preventing delamination caused by the working of the hull This
method requires careful hull preparation and application Further information can be
obtained by contacting Seeman Fiberglass Inc 6117 River Road Harahan and use of hull sheathing systems should not be limited strictly to the the
systems outlined here have demonstrated a successful operational history
Other methods must be carefully considered by the local OCMI on a

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