The 4 Elements Of Sail Trim

[Rick Macdonald]

When twist no longer worked...

I know I should look it up in your book but it's middle of winter and it's more fun talking...When "twist no longer worked and you flatten the sails"...would the flattening of the main be just with mast bend and outhaul, IE leaving in the twist, or would you take the twist out as part of the "flattening" (before finally reefing)?I'm going to guess that the twist stays in to reduce the angle of attack up high (spill wind) to maintain the depowering that twist provides.Geez, I'm really looking forward to next season to try these things out. I've never adjusted the outhaul (nearly impossible because of the 1:1 rigging that we talked about earlier).

 

[Don Guillette]

Rick: The problem is I can't have it both ways. In other words, I can't have the sail as flat as possable and still have it twisted off to spill power. That's not entirely correct because you can never get all the twist out that the sail maker designs into it. He has to design twist into the sail because the wind blows 50% harder at the top of the mast than at deck level. Without some twist you would not be able to control the boat. The wind blows less at deck level because the friction of it blowing across the water slows the wind speed down and that's why you have all the sail trim controls so you can balance the sail.The principle at work in our discussion is that a sail with about 20% to 25% belly (draft depth) equals power and conversely a sail with around 10% belly is less powerful so the first thing you want to do is reduce the belly with the outhaul and mast bend. Draft position aft is more powerful than draft position forward so you want to move the DP forward by using the boom vang, cunningham (or halyard),mainsheet, mast bend and outhaul. The controls for twist are the boom vang and mainsheet and since you have already cranked down on them while adjusting the draft position, you have virtually elininated most of the twist. Additionally, you want to adjust the angle of attack by easing the traveler down.Using all your sail trim controls is like fine tuning a instrument. You put in a little here and take out a little there until you get it where you want it. My suggestion has always been top everyone is that the next time your on the water to take a few minutes and try all the controls. You can actually see the shape changing and once you figure out how they work your miles ahead of most of the sailors worldwide. Rick, when you get the boat on the water, one of the first things you have to fix is the outhaul because, as you know, the outhaul controls the bottom 2/3 of the sail. control .

 

[Don Rice]

Traveller Position Versus Main Sheet

I have read the various threads and I am still confused about the effect of the traveller.When the wind picks up and you want to flatten the sail it makes sense that the traveller is eased and the mainsheet tightened. If the wind continues to pick up I need more twist so the traveller is moved to windward and the main eased.If I am still fighting weather helm I eas the traveller to lessen the angle of attack. Anything beyond this I need to reef. Is this fairly acurate or am I missing something. The other piece is the backstay tension. I have a 35.5 with a substantial rake built into the mast. By tensioning the backstay it would seem to me to create more draft and not flatten the sail but I think I am hearing something different.

 

[Rick Macdonald]

Yes - outhaul!

Considering that my H23.5 has no backstay for mastbend, that only leaves me with the outhaul to adjust the draft depth. All the more reason to improve on that useless 1:1 outhaul setup!

 

[Don Guillette]

Don Rice:Here's the skinny on mast bend. Mast bend changes the shape of the middle and upper portions of the mainsail and it impacts twist and draft position. After the mainsheet, mast bend is the second most powerful controller of mainsail shape and that is why the fast race boats have the ability to bend their mast.The mainsail looks and is called trianglur but it isn't. There is luff curve (extra sail material) built into it and masts are bent because of luff curve. Now if you have a catalina 30 like I do, the mast is like a telephone pole and not really bendable but if you had a J boat, which has a bendable mast, you can get the setup to work performance gains for you.Every seminar participant has trouble understanding mast bend because you would think that bending the mast puts belly into the sail but the opposite is true. Try this experiment. Assume your index finger is the mast. Now bend your finger. See how the knuckle goes backwards. That backward motion is pulling the middle sail material out of the middle of the sail and thus making it flatter. I hope I've helped you understand mast bend.