Wednesday, July26, 2017 L-36.com

Using Target Boat Speed




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Using Target Boatspeed
more than you ever need to know about Target Boat Speed
General Details Polar Diagram I cant sail to these Targets
General
On Target Boat Speed
In a nutshell a target speed is the goal or target speed you try to achieve sailing upwind or
downwind for a given wind speed
Thus if you are sailing up wind on a Soverel 33 in 10 kts of true wind your optimum upwind
boatspeed would be 59 kts with an apparent wind angle of 25 using Soverel 33 Targets v3
for comparison The concept being if you are going too slow you foot off until you Boat Speed
reaches 59 kts and likewise if you are going too fast you pinch up
Note these targets speeds are generated from VPPs velocity prediction programs and do
not take into account unexpected sea states waves from powerboats current chop etc the
weight of your crew the condition of the sails the talent of your crew the condition of the can stop reading if you have satisfied your question the
following is just more boring details
of where Target Boat Speed comes from and how to use them
Details
The Polar Plot
To fully understand Targets and where they come from you need to understand Polars A
polar plot presents a visual of boat speed in relation to True Wind Speed and True
Wind Angle and at times to a apparent wind angle Consider the plot in Figure 1 where Boat
Speed Bs is graphed in relationship to True Wind SpeedTWS for a specific True Wind Angle
Figure 1
Bs versus TWS for TWA 45
For the full range of True Wind Angles a polar plot can be developed where boat speed is
measured on concentric circles True Wind Angles are measured clockwise from the and the plot of boat speed for specific True Wind Speeds Fig 2
Figure 2
Polar Plot for Soverel 33 at 10 kts TWS
Combining the range of True Wind Speeds a complete polar plot is developed In these
examples boat speed is graphed for True and Apparent Wind Speeds of 6 8 10 12 16 and 20
knots
Figure 3
Polar Plot for Soverel 33 Deviation 89 TAR
VMG is defined as velocity made good against the direction of the wind VMG is that portion of
the boats velocity vector which represents the progress of the boat against the wind and is
quantified by the expression VMG Bs x COSTWA where TWA is the the angle between the
direction of the wind and the direction of the boat Fig 4 Thus
True Wind Angle TWS Boat Speed Bs VMG
0 60 kts Bs x 1000 60 kts
45 60 kts Bs x 0707 42 kts
90 60 kts Bs x 0000 00 kts
135 60 kts Bs x 0707 42 kts
180 60 kts Bs x 1000 60 kts
Figure 4
VMC is defined as velocity made good against the course to the mark not the direction of the
wind VMC is commonly confused with VMG Generally a GPS or LORAN will give VMC as the
speed made good towards a mark or waypoint over the bottom not through the water this is
sometimes labeled as VMG by the GPs or LORAN Only when the bearing to the mark and the
bearing of the True Wind are the same will VMC be equal to VMG VMC Bs x COsAm where
Am is the angle between the direction of the mark or waypoint and the direction of the boat Fig
Figure 5
True Wind Speed True Wind Angle
True Wind Speed TWS and True Wind Angle TWA are the speed of the wind relative to the
water and the angle of the wind relative to the bow of the boat respectively Apparent Wind
Speed AWS and Apparent Wind Angle AWA are the vector sums of the True Wind Speed and
angel and boat speed This is the wind you feel as the boat moves through the water and the wind
the sails see Fig 6
Figure 6
TWS TWA AWS AWA
Target The Target speed is the optimum upwind or downwind point on the polar diagram that will
get you upwind or downwind the fastest The Polars show that Target Boat Speed over a long period will produce the best VMG velocity made good for
upwind and
downwind sailing where tacking and jybing are a do you utilize Targets
To some Target Boat Speed is the single most important value to use for beating upwind and
tacking downwind for maximum performance The crew utilizes target speed as the for maintaining the highest potential of the boat upwind and downwind
with between helmsman tactician and sail trimmers
Target Speed theoretical goals
1 develop the best speed for maximization of performance
2 compensates for sailing too high pinching and too low footing
3 compensates for changes in sea conditions smooth water to
rough water
4 allows you to trim sails to optimum angle in theory the jib
Telltales are for trimmers only and the helmsman watches the Boat
Speed
5 promote good team work sail trimmer helmsman and tactician
coordination
6 compensates for different wind velocities
7 promotes proper response to velocity shifts as a result of changes
in wind thoughts on Targets
The best targets you can get are developed thought experience In other words how does
your speed and point compare with other boats
Your own testing and date recording before and during races is extremely valuable data You
can construct your own set of Polars or update existing Polars with footnotes of sail position halyard tension and sea Consider both VMG and the
Polar Chart together From the Polars Fig 3 you know that the
Target Speed point is the boat speed that maximizes VMG for a particular True Wind 7
Figure 7
Target Boat Speed
You know that if you sail too high for too long a time period performance will decrease and if
you sail too low performance will decrease Target Speed therefor is the value which you should
always try to maintain to stay at maximum performance The important concept is to identify the
target speed for a True Wind Speed and then use the target speed to monitor the performance of
the boat and sailing techniques of the crew Apparent Wind Angel or True Wind Angle and VMG
functions do not have the inherent stability to verify your performance upwind or over the entire period of the leg of the course
Target Speed is the upper and lower limit of speeds for sailing upwind and downwind to
maximize performance The telltales will not tell you the whole story over these speed changes If
you are too fast head up When you are too fast you should head up but the telltales will
indicate that you are too high In these instances disregard the telltales until boat target then bear off to hit target at the proper wind angel with
the tell tales if you are too slow bear off to accelerate to Target Boat SpeedThe telltales will tell you
that you are sailing too low again the helmsman should disregard the telltales and the adjust the sails until boat Speed approaches target speed and
then head up so that you hit
target speed at the proper wind angle and adjust the sails Using the apparent wind angle function or Windex to steer by especially at night is slow
The technique emphasizes the coordination required between the trimmer and the jobs of the helmsman and trimmer should be regulated by the Target
Speed Boat
Speed fast head up
If you are too fast
1 Trimmer should trim slightly as you head up
2 As excess speed starts to bleed off Trimmer should ease to allow you to them
bear off and maintain speed again
3 Helmsman should call out above target trim slightly Coming up trim with me
Boat speed slowing east to proper trim at target Or something to that effect
4 Helmsman starts to come down to reestablish target speed
This is a constant loop with constant positive interaction between Helmsman and can then use excess speed to his advantage tactically against other
boats A good
example of this use is in sailing through changing sea states Assume that you are sailing in 23
chop at target speed and the boat enters a smooth condition with 1 chop Boat Speed starts to
accelerate as the boat hits smooth water Use this excess speed to sail higher and gain distance
to weather maximizing slow bear off
If you are too slow
1 Trimmer should ease sails to allow you to bear off and accelerate
2 Helmsman should call out below target ease sheets bearing off
3 As the boat speed builds towards Target Trimmer starts to trim Helmsman
slowly starts bringing the boat back to close hauled
4 When Boat Speed reaches upwind target Helmsman call out Boat Speed at
target full upwind trim and Helmsman settles in at target Speed upwind
Again this is terrifically positive and productive interaction between the crew for performance upwind As the previous example this coordination of
and Target Boat Speed allows you to maintain maximum performance when you enter a
rough patch of water sailing through a current rip or backwash near a shore As the boat enters
the rough water and Boat Speed slows you reestablish target speed quickly allowing you to
preserve your maximum performance for Sea speed can compensate for overall sea conditions
1 In smooth water the boat is able to sail to Target speed while pointing high The
average sailing angle is closer to the wind and target speed is maintained The
same rules apply during shorter changes in sea state too fast head up too slow
bear off
2 In rough seas the Target Speed will remain the same but the average wind
angle will be wider and you will have to sail lower because of the sea conditions
However the theory of target speed s hold true too fast head up too slow bear
Im not competitive when I sail to the Targets
The Targets posted here on the website are for the individual boats as noted For instance the
Targets for Deviation are for using a 143 headsail with a 14 OD size girth Spinnaker Thus if
you have tried the Targets and have failed to be satisfied then you can establish your own
through trial and error which is optimized for you own boat set up and style of sailing
The best targets you can get are developed thought experience In other words how does your
speed and point compare with other boats
Your own testing and date recording before and during races is extremely valuable data You
can construct your own set of polars or update existing polars with footnotes of sail position halyard tension and sea conditions
TWS Upwind Sail Downwind
3 24 143 21 06 oz
5 40 143 37 06 oz
8 56 143 55 06 oz
10 59 143 60 06 oz
12 60 143 64 06 oz
13 61 105 66 06 oz
15 62 105 70 06 oz
18 63 105 78 06 oz
20 63 105 82 06 oz
23 63 105 88 06 oz
25 64 105 93 06 oz
30 65 90 107 06 oz
Sample Duct Tape Strips re Deviation 2002
Three pieces of duct tape in the cockpit can be the most guide on the boat With True Wind
Speed on the first piece of tape Target Boat Speed and Headsail for upwind and Target Speed
for downwind sailing Use the true wind function to reference the target speed boat speed against target speed will maximize your performance As True
wind
changes check your new target speed and respond to maintain maximum Example
1 Helmsman checks True Wind Speed
2 Helmsman identifies target speed for that True Wind Speed
3 Helmsman checks boat speed in relation to target speed
4 If boat speed is slow Helmsman communicates with the Trimmer
to ease the sails bears off accelerates and retrimms
5 Helmsman then rechecks True Wind Speed and so on

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