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Old 23-05-2006, 06:12   #1
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moving traveler to reduce heel

I see everyone here says move leeward to reduce heel.
I was reading a book on sail trim, and it was saying that you should move the traveler to windword and let out the sail to increase twist thus depowering the top of the sail and reducing heel.

So why the difference in opinion.

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Old 23-05-2006, 06:53   #2
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Opening the Traveller forces the boat to a lower angle of oncoming angle of apparent wind; thus reduces the heeling forces by artificially moving the CE of the mainsail forward (by the magic of 'mathematics') .... this is for when the boat is becoming overpowered.

The 'trim article' you were reading apparently is concerning sail trim to maximize the forward thrust from the sails by 'depowering (but not being overpowered) and to shape/set to get maximum thrust for the current wind conditions. Simply loosening the vang and the slightly loosening the mainsheet will add twist aloft to help depower. .... but this leads to an a possible 'unstable' (cranky) mainsail with all kinds flow separation/stalling at various places on the sail ... . What will happen when overpowered with lots of twist aloft and the foot of the sail overtightened is no real loss of weather helm but the boat slows down thus becomes more vulnerable to get knocked even further over .... the air stream flow attaching sometimes to the lower section of the sail, sometimes at the head as the sail 'oscilates' between the two.

Usually when weather helm develops when overpowered its usually a design fault of the hull (broad-assed stern, etc. or other non-symmetry of the hull) OR improper sail shape where the 'postion of maximum draft' is too far aft in both foresail and mainsail --- ie.: not enough halyard tension, etc. A boat with a symmetric hull shape and properly shaped/set sails when overpowered by a gust, etc. will simply lay over / heel a bit more .... but will definitely NOT develop more weather helm.

Better to use the traveller and keep the airflow attached --- by watching the performance of the telltales at mid cord and leech of the sail ... and 'blade-out' (precisely 'feather' but still keeping the flow 'attached' to the sail to keep control while at the same time - reducing heel.

For a very precise non-intuitive aerodynamic analysis for the usage of
'tell tales' go to .... look up the "magazine articles", then select all the articles for trimming:
• Checking Trim on the Wind, November 1973
• Achieving Proper Balance, December 1973
• Sailing to Windward, January 1974
• Are You at Optimum Trim?, March 1974

These are the 'seminal' articles that set the sailing world on its ear and destroyed the 'intuitive' thought process of how a sail works, how to trim/shape, debunked the 'slot effect', etc. etc. etc. .... and was the reason why the US Americas Cup boats dominated the sailing world for many years. Especially see the articles that use 'tell tales' and 'gentry tufts' for sail shaping and trim. Although these articles were written for the 'layman', unless you have an 'aero' background you wil need to read them over and over several times before they make sense. Aerodynamics of SAILS **cannot** be explained by 'intuitive thinking'; although, you can see the affects by the usage of telltales.

Hope this helps.

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Old 23-05-2006, 07:16   #3
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Maybe you just need to go out and buy more books...

but I think it's better to get out of your reading chair, turn off your computer and get out on your boat! Cast your lines and tweak with the traveler, fairleads, halyards & outhaul tensions and figure out for yourself what makes YOUR boat work best.

An adage I learned in the Navy applies well to sail trim:

"I Hear & I Forget - I See & I Remember - I DO and I UNDERSTAND"

Come on - it's SPRINGTIME! Get off your a$$ and go sailing!

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Old 28-05-2006, 16:31   #4
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Trimming sails when cruising is, for me, a lot different from trimming when racing. When I am crusing, going hard to waindward, if the breeze gets up such that I cannot keep the boat "on its feet" (i.e less than 15 degrees of heel, approx) by flattening the mainsail with outhaul and cunningham, keeping it sheeted in hard, but fully down the traveller, then it is time to start thinking about shortening sail.
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Old 28-05-2006, 20:04   #5
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Good advice above.. I'll risk oversimplifying this by saying that when close-hauled your mainsheet pulls your sail down and makes it flatter, while the traveler controls the in-out angle. Flatter sail is better in a strong breeze, so keep the sail flat and let the traveler down to leeward. If you need to ease the sheet all the time to open up ("twist") the top of the sail to avoid heeling too much, then you're carrying too much mainsail and it's time to reef. After you've reefed, you still want a flat sail, not a baggy one.

Hope this helped.
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Old 29-05-2006, 07:00   #6

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I think the best book on trim I've ever read is "The Best of Sail..." something like that, from Sail Magazine, a compendium of their articles on trim.

Part of the conflict you are seeing may come from different needs. If the winds are variable you may "play the traveler", just letting the traveler out to depower and then equally rapidly pulling it back up, constantly playing the traveler position to keep the boat on its feet with full power but not overpowered. I don't know any way to respond that rapidly in shifting winds if you are going to work BOTH the traveler and the main, there's a limit to how many hands I have.<G>

On the other hand if the wind was building but not constantly puffing and dropping, sure, it might be more effective to trim the main that way. Playing the traveler is not "instead" of trimming the main, it is just a fast way to keep responding to variable strong wind speeds after the main has been trimmed.

If you are overpowered in a puff, you'll probably develop immediate weather helm and heel, and then the helmsman has to use the barn door (the rudder aka the big brake) to compensate. But if you play the traveler, you can ensure the helmsman has an easier job and isn't using the brake--and that makes you faster.

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