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Checking Trim On The Wind


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Checking Trim on the Wind Arvel Gentry Outlines a Useful System By Arvel Gentry SAIL Magazine November 1973 Sailing fast to windward involves a complex interactionof sail shape and trim boat balance and helm and how thetiller is moved in response to each wave or crosschopThere are optimum tradeoffs for all these sail trim factorsand they must become almost an automatic reflex December 1999 Making a boat go fast usually comes with experiencebut this learning process can be shortened by developing asound approach to trimming the sails and for steering theboat This month I will describe my own to making a boat go fast to windward bydiscussing the basic sail trim settings for the genoa andmainsail Obviously no single article can possibly cover everyaspect of sailing to windward and Ill just try to touch on afew aspects of the problem that I think are I will assume we are sailing a keel boat ofMORC size or larger with a masthead rig and As I proceed with the various steps in trimming thegenoa and mainsail keep in mind the following effects that occur between the two sails First the genoa causes a slowing down of the slot air Photo 1 Telltale and tuft over the forward leeside of the mainsail Just theright amount of slowing down of the slot air will be In practice I find that flow separation on the for it permits the mainsail to be sheeted in at a side of the sails is the key factor that controls what we do intight angle without stalling Thus the genoa helps keep trimming them Separation on the windward side is notthe mainsail leeside from separating nearly so important While we cant see air we can see However if the genoa is sheeted too close or the main what it does to our sails and to pieces of yarn or ribbonlet out too far the pressures will become the same on both telltales that we attach to them But where to put thesesides of the mainsail It will then start to shake commonly telltales and how to use them are questions that are worthcalled backwinding and its contribution to the total studying in detaildriving force will be reduced Id like to do two things in the following discussion A properly trimmed mainsail creates an upwash flow First help you establish your own systematic approach tofield in front of the genoa a wind shift corresponding to a trimming the sails Second help you learn what thelift which allows the boat to be sailed closer to the wind different sail adjustments actually are doing to your sailswithout the genoas luffing Photo 1 shows the telltale system I use Ive numbered The high velocities created by the mainsail in the region each telltale on the photo for easy reference The telltalesof the genoa leech cause increased velocities and reduced are made from 12 by 6 strips of 05 oz spinnaker clothpressures all along the lee side of the genoa This gives the The strips are cut with a pointed soldering iron using agenoa its great drive and also helps keep the leeside genoa metal straight edge plastic tape is used to attach them toflow from separating Proper mainsail trim is very the sail I find these ribbons more responsive in light windsimportant in getting the most out of the genoa than telltales made from yarn although they do tend to I described all these effects in more detail in past articles stick to the sail when wet Each of the numbered telltalesSAIL AprilAugust 1973 has its own purpose in achieving the proper sail trim As we search for proper sail trim we attempt to find the To aid in steering the boat Ive developed a system ofbest compromise between all these effects We want the short 4 ribbons that are placed near the luff of the genoagenoa to help the mainsail without pushing it to the point This system is marked with the letter T in Photo 1 I refer towhere the mainsails contribution to the total driving force these as tufts and to all of the other ribbons on the sails asis reduced And we want the mainsail to be trimmed telltales The tuft system SAIL May 1973 consists of onetightly enough so that it gives the maximum help to the short ribbon right on the rope luff two more in a plasticgenoa leech velocities without reducing its drive window and one just aft of the window The portsidetufts are red and the starboard ones green The plastic window is put as close to the luff tape as ispossible for it is important to be able to see the first twotufts The tufts are attached to the window tape The same tuft arrangement can be usedwithout the window but it may be difficult to see themunder certain lighting conditions The leeside telltales tell when the air has separatedfrom the surface of the sail The air in these is rather mixedup and unsteady and causes thetelltales to twirl wildly When the air is from the lee side of a sail it is stalled and itsforward driving force is greatly reduced However Photo 2 Tuft system Headstay and jib luff are at far rightseparated flow on only a portion of a sail can be almost asbad and will put you out of contention quickly time only gives the approximate genoa car location for This partial separation occurs most frequently on the overall sail shape is frequently even more of a sail and is particularly important on the Write down the genoa car location number thenmainsail and on the genoa under certain conditions When observe telltale 7 as the car is moved way forward anda sail is not generating lift because it has too low of an angle again when it is moved too far aft Always sail with tuft T 1to the wind it will shake or luff However when it has too just lying down smoothly but the sail at T not luffing Fromhigh an angle you cant tell from the sail shape you must this exercise you will see how different amounts of twistlook at the leeside telltales affect the flow over the luff of the sail When I start sailing on a new boat I first install the Now return the genoa car to the location you havetelltales and tuft system shown in Photos 1 and 2 Next marked Sail with the first tuft at T 1 showing just a slightwith a label maker I put numbers by each genoa track amount of agitation Check all the leeside telltales on thescrew on the traveler outhaul and on the mast for halyard genoa If any of the leech telltales 3 4 6 and 8 aretension I also wrap a piece of tape around the spreader six twirling then try increasing the halyard tension andinches in from the end and another twelve inches in letting the sheet out a bit to maintain the same distance offThese help me judge the distance the genoa is lying off the the spreader At this point we still may not have exactly thespreader correct genoa car location or halyard tension But before Next I begin to check sail trim while beating Ill assume we spend more time on the genoa lets switch ourabout 8 to 10 knots of wind To begin I guess at genoa attention to the tension and fairlead position The genoa is The mainsail has a strong influence on the flow over thetrimmed so that it lies three to four inches from the genoa and we should be sure it is trimmed properly beforespreader and the mainsail is set so that it is not luffing All we worry further about the genoa The mainsail isare just approximate positions controlled by the mainsheet traveler outhaul The first task is to check the genoa car location The cunningham vang leech chord batten stiffness and mastusual way to determine this is to sail close hauled luff the bend The mainsheet and traveler however are the keyboat up then adjust the genoa car so the genoa luffs evenly adjustments for they affect mainsail position and twistall along the luff To start set the traveler on the centerline Let way out However I have a different approach that I believe is a on the mainsheet and then pull it in as you watch the topbit more precise First sail the boat precisely on the wind leeside telltale 13 Stop when 13 twirls and let the sheetby making all the leeside tufts at T lie down The part of the back out until it lies downgenoa at T is then just on the verge of luffing Now look at Now check the lower part of the main near the mast totelltale 7 Photo 1 at the top of the genoa luff If it is see if it is being backwinded by the genoa Personally Itwirling the sail needs to twist off more so move the jib dont like the term backwinding for it seems to imply thatfairlead aft a bit If the sail is luffing at 7 it has too much the genoa is throwing air against the lee side of the maintwist up high so move the fairlead forward Again sail and this is not what is happening at all The mainsail is justprecisely on the wind with all the tufts at T lying down reacting to an increase in leeside pressure resulting from Now have the helmsman start to bear off slowly and the genoas slowing down of the air in the slot SAILfrom the pulpit watch both the first leadingedge tuft at T August 1973 However everyone does seem to use the1 and telltale 7 As you start to bear off both these ribbons term and therefore I will toowill suddenly twirl as a small separation bubble forms all If the main is being backwinded move the traveler toalong the luff The sail is not stalled it only has this small windward until the backwinding stops Now readjust theseparation bubble all along the luff SAIL May 1973 mainsheet again until the top telltale 13 twirls then just lies If the twirling starts at 7 and T1 at the same time the down again Repeat these is coming into the sail at about the same angle all until the sail is not being backwinded and the top telltale isalong the luff Again this use of telltale 7 and tuft T1 at this just lying down 2 If the genoa has a large amount of overlap a 180 In this way you will see how mainsail trim does affect thegenoa for example it may be difficult to stop the back air flow over the genoawinding without pulling the mainsail so tight and so far to You should have the two sails trimmed pretty well bywindward that the mainsail leech hooks sharply to this time However a number of questions are yet to bewindward To fight this problem first try tightening the resolved How good is the boats balance Is there tooouthaul If this doesnt work try increasing by an inch or so much lee or weather helm How is the shape of the genoathe genoas distance off the spreader Should we barber haul it and how much What about sail Now check the mainsail leech telltales 10 12 and 14 If trim in very low or very high wind conditions And finallyany of them is twirling and 9 11 and 13 are not you have a how is the tuft system used in steering the boat toleech flow separation problem because the leech is windward Next months article will pursue thesehooking too far to windward First tighten the outhaul and questionsthen the cunningham to let the leech fall off someRemember when you apply tension to one edge of a sailthe other edge will falloff some You also may have to movethe traveler down a bit If the bottom row of telltales 9 and 10 are twirling thelower part of the mainsail is either in too tight or the genoais not trimmed in enough Move the traveler to leewarduntil they settle down and adjust the mainsheet until thetop row of telltales again are lying down Your mainpurpose in all this is to learn how to coordinate the travelerand mainsheet tension to get the proper twist in the sail After a few repeated cycles of these adjustments writedown or mark the traveler position so that you can returnto it Now observe the mainsail leeside telltales as thetraveler is moved further to windward The leech telltales10 12 and 14 will twirl about the same time by 9 11 and 13 as the complete sail stalls This tellsyou that all parts of the mainsail are working equally hardin generating lift and in helping the genoa Now return thetraveler to its proper best position Sight up along the mainsail and see if the top batten ishooking to windward of the centerline of the boat If it isthen you may not be getting maximum forward drive outof the upper part of the sail even though telltales 13 and 14are lying down Let the leech fall off so that it does nothook to windward by letting out the mainsheet a bit andmoving the traveler slightly to windward If this 10 or 12 to twirl then increase the and again adjust the mainsheet and traveler to getall of them to lie down Whatever you do always trim the sail so that telltales 13and 14 are lying down sometimes if you trim the main sothat the top battens are pointing straight aft telltales 13and 14 will be twirling and the upper part of the sail will bestalled so using just the batten alignment procedure maylead to bad mainsail trim After the mainsail is trimmed turn again to the genoaWatch the genoa tuft system at T and telltale 7 first as theboat is sailed precisely on the wind and then as you bearoff slightly to see if the mainsail adjustments have had anyeffect on proper genoa settings If they have then repeatthe genoa trim procedure As an experiment try sailing only with the T 1 tufttwirling in steady wind and smooth water Then let thetraveler way out and move it all the way windward to stallthe sail and watch what happens to the T 1 tuft each time 3


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