Mates: I wrote this article many months ago. It may be of interest to beginners to intermediates who are visiting Sailboatowners.com for the first time. Sail trim is actually a small body of knowledge but unfortunately a lot of folks think it is nuclear research. Once you understand what is happening to your sails, the concept of sail trim becomes very understandable. In fact, you'll wonder why you were so confused, when you first started to try to understand it. The Four elements Of Sail Trim To take the mystery out of sail trim is to essentially understand that all the controls for the mainsail and jib only adjust four things and they are: Draft Depth (belly) Draft Position Twist Angle Of Attack Lets start with the first two elements. Why do we have to understand Draft Depth (belly) and Draft Position ? We have to understand them because they control three things - POWER, ACCERERATION and DRAG. Drag, is actually friction, which detracts from power and comes from the rudder, keel etc. A sail is like an airplane wing and if a plane flew sideways it would be called a sailboat. The plane's flaps, in the up or down position , produce a deep shape ( like a belly) and are used for takeoffs and landings. No flaps or a flat wing create less drag and are used for high speed and cruising. Where does the POWER to power a sailboat come from? It comes from three things and they are the SHAPE of the sail, which is either deep or flat. The power also comes from TWIST. Twist is the most important sail trim adjustment you can make. I'll go into the definition of twist in a later message. The final element of power is the ANGLE OF ATTACK and I'll go into the that definition later also. What is DRAFT DEPTH (belly)? It is " the % of sail width at a given point". To understand that definition we have to discuss DRAFT POSITION, which is " the point along the chord where the maximum depth falls". To find the chord you measure the foot of the sail and mark the halfway point on the boom. In other words, if the chord is 10' long then the 5' mark would equal 50%. The 4' mark would equal 40% and so on. So, if the belly of the sail was 1' deep then the draft depth would be 10%, which is a relatively flat sail. If the belly was 2' deep then the draft depth would be 20%. Now, you have to imagine a vertical line going up the middle of the belly of the sail. Where that imaginary line intersects the boom is called the draft position. Assume the skipper of the boat decided that the point of sail and wind condition he was sailing in would need a 20% draft depth and a 50% draft position to obtain 100% efficiency from his mainsail. You know what setting you have to obtain and that is a 2' belly with the imaginary line falling at the halfway point on the chord line. You may not know what controls to use or which way to trim them but we'll get into that later. It is very important that you understand draft depth and draft position before we go any further. Any questions on the above two items?
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A
Alan
Got it !
I don't know if you need a response, but I'm ready for Step 2! Not to get ahead of the game, but will we be covering sail batten tension also?
I don't know if you need a response, but I'm ready for Step 2! Not to get ahead of the game, but will we be covering sail batten tension also?
G
Glenn Greene
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Paul
% draft depth definition
Don, Just a quick clarification....so the draft depth % is based upon the overall chord length? If the cord of my main, ie bottom edge of the main, along the boom, is 10ft, then a belly depth of 1ft is a depth % of 10%. Then I understand that the actual position % of the belly is from front to back along the boom. Thank for this series of discussions..... Paul
Don, Just a quick clarification....so the draft depth % is based upon the overall chord length? If the cord of my main, ie bottom edge of the main, along the boom, is 10ft, then a belly depth of 1ft is a depth % of 10%. Then I understand that the actual position % of the belly is from front to back along the boom. Thank for this series of discussions..... Paul
D
Don Guillette
Paul: Draft depth (belly) and draft position are like a 2 dimensional thing with the mainsail and the jib and you look at them together but they are separate items. You've got the concept of the belly part. If you had a 1' belly it would be 10% on a 10' chord. If you had a 2' belly it would be 20% and so on. Belly doesn't care where it falls along the boom from front to back. It only cares about how deep the sail is. Draft position, on the other hand, does care about its position on the boom. What you would do to determine draft position is first check the belly and look for the deepest spot in the sail. Then you'd draw an imaginary line from top to bottom, right through that deepest spot and see where it intersects on the boom. If it hits at the 5' mark, than your at 50%. It it intersects at 4'6", then your at 45%. This all seems complicated at first, but once you get the hang of it, you can do it in 5 seconds or less. Why is this knowledge so critical? It is all about power and that is what draft position and draft depth are all about. Soon, I'll be explaining what sail trim controls are used to control draft depth and draft position so you can go out on the water and experiment on your own boat, but unless you understand exactly what I'm talking about it won't make any sense.
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Don Guillette
Alan: Batten and also telltails are very important items that serve as indicators that suggest the need for a sail trim adjustment by using a particular sail trim control. So, you can see that battens and telltails are not actual sail trim controls, but it is important to understand what they are telling you. What battens do is provide rigidity to the leech of the mainsail. Rigidity to the luff is provided by the mast and the foot of the sail gets it's rigidity from the boom. Without battens, the sail would sort of be as limp as a dish rag. Without them you could not control the shape of the sail or the draft depth. The problem with discussing this stuff on this forum is you get the information in small doses. I tell students at the beginning of sail trim seminars I conduct, that I wish I could open their heads and pour in the information all at once!! I tell them to be patient because in 3 hours they will know more about sail trim than 75% of the sailors worldwide. The first hour is very critical and confusing to beginners and intermediates but once I get past draft depth, draft position, twist and angle of attack the lights start to go on. The advantage of the seminar is obvious - I discuss it, demonstrate it and answer questions. Obviously, I can't do all those things on this forum but you can get the next best thing. My book "The Sail trim users Guide", which is available on this site, is the text that is used in the class. In other words, reading the book is like being in the class. My Email address is listed in the book and I welcome any questions about any of the material covered. Actually, I don't get a lot of questions because the material is presented in plain and simple English - no complicated formulae or scientific presentations with intricate details. Just the facts you need to know in order to get 100% efficiency from your sails
T
Tom Monroe
N
Noah
Can you have 100% draft depth?
I can understand 10, 20, and 30 percent depth, but what would a 100% draft depth look/be like?
I can understand 10, 20, and 30 percent depth, but what would a 100% draft depth look/be like?
D
Don Guillette
The 4 Elements Of sail Trim
Noah: A 100% draft depth is not possable to obtain. In our example, which has a 10' chord, you could not get a 10' belly , which would equate to a 100% draft depth - nor would you ever want to. You couldn't even get a 50% draft position, nor would you ever want to either. To get a 5' belly, you'd have to disconnect the clew from the outhaul and attach the clew somewhere very near the tack of the sail.The max draft depth you want is around 25%. Interesting question, which I had to think about for a minute. In over 25 seminars, no one has ever though of that question.
Noah: A 100% draft depth is not possable to obtain. In our example, which has a 10' chord, you could not get a 10' belly , which would equate to a 100% draft depth - nor would you ever want to. You couldn't even get a 50% draft position, nor would you ever want to either. To get a 5' belly, you'd have to disconnect the clew from the outhaul and attach the clew somewhere very near the tack of the sail.The max draft depth you want is around 25%. Interesting question, which I had to think about for a minute. In over 25 seminars, no one has ever though of that question.
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Alan
Battens
Don, On my boat the tension on the sail battens is adjustable dependant on wind conditions. I was simply wondering if after we cover the 4 basics we could get into this adjustment?
Don, On my boat the tension on the sail battens is adjustable dependant on wind conditions. I was simply wondering if after we cover the 4 basics we could get into this adjustment?
C
Colin Cheetham
Don...availability of books
Don I have followed most of your posts with interest and I wondered if you know whether your books are available here in the UK?
Don I have followed most of your posts with interest and I wondered if you know whether your books are available here in the UK?
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Don Guillette
The 4 Elements Of Sail Trim
Colin: Greetings from the colonies!! Yup, both my Sail Trim Chart (which gives you the sail trim adjustment for all the sail trim controls on your main and jib for every point of sail and wind condition) and my book The Sail Trim Users Guide (which tells you WHY you are making a particular sail trim adjustment)are available to be shipped worldwide. All you have to do is contact our host,sailboatowners.com at 206 932-7245 or fax 206 285-3387 and place an order. Ask for Karisa, who manages the ship store. She'll see that my products are in the mail to you the day you place your order.
Colin: Greetings from the colonies!! Yup, both my Sail Trim Chart (which gives you the sail trim adjustment for all the sail trim controls on your main and jib for every point of sail and wind condition) and my book The Sail Trim Users Guide (which tells you WHY you are making a particular sail trim adjustment)are available to be shipped worldwide. All you have to do is contact our host,sailboatowners.com at 206 932-7245 or fax 206 285-3387 and place an order. Ask for Karisa, who manages the ship store. She'll see that my products are in the mail to you the day you place your order.
D
Don Guillette
The 4 Elements Of sail Trim
Alan: I'm at a loss on these Hunters as I've never had the opportunity to sail on one and I really want to as Hunter owners keep telling me their boats sail differently than a convential rig, which I don't understand. At the last sail trim seminar I conductors, a couple of Hunters owners offered me a test drive but it has not taken place yet. There is also a Hunter on my dock but I never see the owner so I can talk to him and I'm there most of the time.What kind of a sail trim control does Hunter provide that allows you to adjust only the battens? What sail trim controls do you have for the main - cunningham, boom vang, traveler, outhaul and I assume you can't bent the mast? Any help you can give me will be appreciated.Are there any Hunter owners out there that can help with Alans problem?
Alan: I'm at a loss on these Hunters as I've never had the opportunity to sail on one and I really want to as Hunter owners keep telling me their boats sail differently than a convential rig, which I don't understand. At the last sail trim seminar I conductors, a couple of Hunters owners offered me a test drive but it has not taken place yet. There is also a Hunter on my dock but I never see the owner so I can talk to him and I'm there most of the time.What kind of a sail trim control does Hunter provide that allows you to adjust only the battens? What sail trim controls do you have for the main - cunningham, boom vang, traveler, outhaul and I assume you can't bent the mast? Any help you can give me will be appreciated.Are there any Hunter owners out there that can help with Alans problem?
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Alan
Controls
Don, Hunter did not provide the tension adjustable batten pockets, my sailmaker did. I use IOR style tapered foam core battens that sit in the pocket held by velcro straps. As for the main controls,the main sheet I designed and had made a double line course/fine 5:1/10:1, cunningham is 2:1 lead aft, vang is Hall solid w/ 16:1, traveler controls I modified from 3:1 to 5:1,outhaul is spectra internal 8:1,and yes I can bend the mast with my backstay(masthead moves more than a foot) I also have a jumper strut at the hounds so that backstay not only bends the mast but tensions the headstay at the same time.
Don, Hunter did not provide the tension adjustable batten pockets, my sailmaker did. I use IOR style tapered foam core battens that sit in the pocket held by velcro straps. As for the main controls,the main sheet I designed and had made a double line course/fine 5:1/10:1, cunningham is 2:1 lead aft, vang is Hall solid w/ 16:1, traveler controls I modified from 3:1 to 5:1,outhaul is spectra internal 8:1,and yes I can bend the mast with my backstay(masthead moves more than a foot) I also have a jumper strut at the hounds so that backstay not only bends the mast but tensions the headstay at the same time.
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Don Guillette
Controls
Alan: I'm aware of stiff, very stiff and soft battens plus short and long battens.I know where they go and when to use them but I've not experieced tension adjustable batten pockets. How does the system work when your sailing? How do you use the system? Suppose the wind conditions change, what do you do and why?
Alan: I'm aware of stiff, very stiff and soft battens plus short and long battens.I know where they go and when to use them but I've not experieced tension adjustable batten pockets. How does the system work when your sailing? How do you use the system? Suppose the wind conditions change, what do you do and why?
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