Sail Trim Users Guide

[Bullshooter]

I hope to never be too old to learn, and I bought the book by Don Guillette, The Sail Trim Users Guide, as recommended by some posters. It may just be me, but I had a bit of trouble understanding some things in it. For instance, (and although I understand that several different things control sail shape), he seems to contradict himself in this way:

After noting on page 12, that a deep sail produces more power and is used in light or medium air, he states:

“The general rule is to trim the sail as full or with as much belly as possible. ”
He says on page 14-15 that “A draft position FORWARD produces less power and is more forgiving.” And that “Increasing mainsheet tension moves draft position FORWARD. “

Then on page 23 he says, in MODERATE AIR TRIM:
“Trim the mainsheet in hard to the point of partial stall. When the boat is slow, ease the mainsheet very slightly to partially twist out the top of the mainsail.”

(The underlining is mine).
So if medium air and moderate air can be taken as the same thing, it appears that he says that you should sail with as much belly as possible (p. 12) but then later says to trim the mainsheet hard, which produces less power (p. 23) and would flatten the sail.

I am not posting to criticize the book, but rather in hopes someone might help me understand what he means here. My practice is to trim the mainsail almost to the point of luffing, then ease the sheet to allow some twist IF there is too much heeling or weather helm. If that results in luffing, or poor telltale behavior, adjust traveler, etc. In other words, I don’t start out to trim the mainsheet in hard. If I want to gain power, I can also ease the outhaul for more depth.

Your comments are welcome.

[sailingharry]

I didn't follow all of your twists, although I'm sure if I read with more focus I could. But I think I understand the conflict on deep draft. He says you want it as deep as possible, and then talks in several areas about flattening the sail. Two big things that deep is bad for. First, deep does not allow you to point up wind, the flatter the sail is the closer to the wind you can sail. Second, deep induces heel, and so in heavier airs, flat makes the boat more manageable. In both of these situations you want the sail deep, but the caveat "as deep as possible" means you can't have it deep.

Let me go read back through and see if there's some other questions you were asking.

[thomm225]

Originally Posted by Bullshooter

I hope to never be too old to learn, and I bought the book by Don Guillette, The Sail Trim Users Guide, as recommended by some posters. It may just be me, but I had a bit of trouble understanding some things in it. For instance, (and although I understand that several different things control sail shape), he seems to contradict himself in this way:

After noting on page 12, that a deep sail produces more power and is used in light or medium air, he states:

“The general rule is to trim the sail as full or with as much belly as possible. ”
He says on page 14-15 that “A draft position FORWARD produces less power and is more forgiving.” And that “Increasing mainsheet tension moves draft position FORWARD. “

Then on page 23 he says, in MODERATE AIR TRIM:
“Trim the mainsheet in hard to the point of partial stall. When the boat is slow, ease the mainsheet very slightly to partially twist out the top of the mainsail.”

(The underlining is mine).
So if medium air and moderate air can be taken as the same thing, it appears that he says that you should sail with as much belly as possible (p. 12) but then later says to trim the mainsheet hard, which produces less power (p. 23) and would flatten the sail.

I am not posting to criticize the book, but rather in hopes someone might help me understand what he means here. My practice is to trim the mainsail almost to the point of luffing, then ease the sheet to allow some twist IF there is too much heeling or weather helm. If that results in luffing, or poor telltale behavior, adjust traveler, etc. In other words, I don’t start out to trim the mainsheet in hard. If I want to gain power, I can also ease the outhaul for more depth.

Your comments are welcome.

You learn these things racing rather quickly.

To stay near the leaders in light winds, I/we ease the sheets and the downhaul. And if you have time maybe the outhaul but many times that isn't necessary. We also rake the mast more forward.

In heavy air, we downhaul the luff hard, and sheet in hard and on top of that if we know it will be a heavy wind day, we crank in more prebend in our rigging. Also rake the mast back more.

Sometimes in heavy air we also ease the main traveler out some and de-rotate or over rotate the mast if you have a mast that rotates.

The prebend bends the mast forward near the center which stretches the mainsail even flatter. On catamarans (beach cats) we do that with the diamond wires on a monohull with two lowers we crank in the forward lowers maybe 100 psi more than the stern lowers

My experience is about 450 races.......

Medium air midrange depending ......

Here's the thing though.

You can have your boat set up perfectly, but if you sail say in the opposing current you can still lose the race or end up DFL (dead F'ing last!)

[wholybee]

Originally Posted by Bullshooter

I hope to never be too old to learn, and I bought the book by Don Guillette, The Sail Trim Users Guide, as recommended by some posters. It may just be me, but I had a bit of trouble understanding some things in it. For instance, (and although I understand that several different things control sail shape), he seems to contradict himself in this way:

After noting on page 12, that a deep sail produces more power and is used in light or medium air, he states:

“The general rule is to trim the sail as full or with as much belly as possible. ”
He says on page 14-15 that “A draft position FORWARD produces less power and is more forgiving.” And that “Increasing mainsheet tension moves draft position FORWARD. “

Then on page 23 he says, in MODERATE AIR TRIM:
“Trim the mainsheet in hard to the point of partial stall. When the boat is slow, ease the mainsheet very slightly to partially twist out the top of the mainsail.”

(The underlining is mine).
So if medium air and moderate air can be taken as the same thing, it appears that he says that you should sail with as much belly as possible (p. 12) but then later says to trim the mainsheet hard, which produces less power (p. 23) and would flatten the sail.

I am not posting to criticize the book, but rather in hopes someone might help me understand what he means here. My practice is to trim the mainsail almost to the point of luffing, then ease the sheet to allow some twist IF there is too much heeling or weather helm. If that results in luffing, or poor telltale behavior, adjust traveler, etc. In other words, I don’t start out to trim the mainsheet in hard. If I want to gain power, I can also ease the outhaul for more depth.

Your comments are welcome.

I don't have this book, but to address your questions.
Moving the draft fore or aft is not the same as the size or how deep the draft is. I presume by "more forgiving" he is referring to widening the groove. That is, the boat might be a bit slower, but the angles you can sail where the tell tails fly correctly is wider, so you can steer over chop a bit without stalling the sail. With a narrower groove, the boat is faster, but it is a very narrow range you can steer and still maintain speed.

I don't read "light or medium air" as the same as "moderate" air. I consider moderate air to be a pretty good breeze. Not to the point of being heavy, but for sure more than light or medium. In a moderate wind with full sail, you are at the max wind before needing to reef.

Does he talk about "gears" at all in the book? That might be the concept he is getting at on page 23. Over trimming a sail is fast, but lacks power, like high gear in a car. Over trimmed you might be able to maintain speed, but not get up to speed. To get up to speed, you downshift, by under trimming the sail. Not as fast, but more power to accelerate to speed.

Does he talk about the "whys" of sail twist? There are 2 reasons. One is because you are overpowered and want to spill wind. Similar to reefing, but dynamic and fast to do- make the top of the sail not work anymore. The other is because the apparent wind direction is different at the top of the sail from the bottom of the sail. Air close to the water moves slower than air higher up. Because apparent wind direction is related to true wind speed, a sail perfectly trimmed from top to bottom will have a bit of twist.

Keeping that in mind, if the sail has no twist, it is not perfectly trimmed over the whole sail. But as you turn a few degrees one way or another, there will always be part of the sail that is perfect. That is why a flat sail is more forgiving. And if you need a bit more power, ease it and let in some twist.

I think the most helpful thing is to go sailing and watch your tell-tails. Note that quite often some will be flying perfect, but not all of them. Play with twist to get them all flying. Note how to do that with the mainsheet on the main, and car position for the jib. Next, with perfect trim, head up a few degrees, or down a few degrees. Note how the boat slows, and how much or little you can turn when that happens. Now, adjust the twist and do that again.

Also, observe the sail. Watch the draft. Is there a "bubble" against the mast, or further aft? Ease the sail and trim the sail, and observe what the draft looks like when perfectly trimmed. There is a saying "if in doubt, let it out." Without using the tell-tails, you can ease the mainsheet until the draft starts to collapse, then trim in until it is full. That is very close to perfect. But it looks about the same as if you are over trimmed. So, let it out until it looks wrong, then trim in.

Anyway, I rambled on a bit. I hope it helps.

[wholybee]

Originally Posted by sailingharry

I didn't follow all of your twists, although I'm sure if I read with more focus I could. But I think I understand the conflict on deep draft. He says you want it as deep as possible, and then talks in several areas about flattening the sail. Two big things that deep is bad for. First, deep does not allow you to point up wind, the flatter the sail is the closer to the wind you can sail. Second, deep induces heel, and so in heavier airs, flat makes the boat more manageable. In both of these situations you want the sail deep, but the caveat "as deep as possible" means you can't have it deep.

Let me go read back through and see if there's some other questions you were asking.

"as deep as possible" is the key. A deep draft has more power. A flat sail has less. So, at wind picks up and you start to be overpowered, you flatten the sail. You do always need _some_ draft. Draft provides lift which drives the boat forward. Without lift, you might seem to point well, but will have lots of leeway, as there isn't lift driving the boat forward. So, even pointing as high was possible, the sail isn't completely flat.

The other oddity, is that in VERY light wind, too much draft will cause the air to detach from the sail and stall. So, even though a flat sail depowers the sail, and draft adds power, in really light wind you need to flatten the sail for good airflow.

[DEAN2140]

I think you understand trim quite well. Just keep doing what you are doing.

[Bullshooter]

Thanks to all that responded. I think I will keep doing what I've been doing. I am mostly not racing, so I just try to get the most speed, or sometimes VMG, and experiment with what helps and what does not.

[Stu Jackson]

BS, your questions are reasonably valid. If I ever have a question about what an author means, I try to ask the author. AFAIK, Don rarely, if ever, reads this forum. He is however active here: https://sbo.sailboatowners.com/recent-fx.php He is a frequent & featured contributor there. Don & I correspond regularly and have been doing so for 20 years.

[alctel]

It's worth noting that you want a different amount of belly in the sail depending on the sea state as well