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Old 23-03-2013, 22:50   #16
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Re: Sail Trim - True vs. Apparent Wind

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Originally Posted by daddle View Post
That can't be right. Twist is always the other way.

The secret to trim is to adjust the sails to suit the conditions. Takes many years of practice. Books and text are useless. Going sailing is the only way. Going with experienced people, racers perhaps, is the best.

The top batten parallel to the boom does give the sail twist. Most tuning guides give this as a starting point for twist. A couple of leech tell tales one near the top batten and one 1/3 up is a great way to trim the main upwind. They only tell you stall, not luff. Bring the traveller up to windward until the lower leech telltale starts to break, then reduce twist by pulling in the mainsheet until the top telltale starts to break.

North sail tuning guide saying top batten parallel:
North Sails: Set Twist
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Old 23-03-2013, 22:56   #17
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Re: Sail Trim - True vs. Apparent Wind

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Originally Posted by Jammer Six View Post
It's extremely difficult to know the true wind aboard a sailing vessel. And if you did, the next instant you'd be wrong again.
It was extremely difficult until the invention of GPS and electronic instruments (besides apparent wind info you only need SOG and COG info from GPS to know true wind). Modern instruments calculate this accurately ten times a second and the value must be damped so that humans can work with it.
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Old 23-03-2013, 23:01   #18
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Re: Sail Trim - True vs. Apparent Wind

The top batten lined up with the boom is a good starting point. If you want super high pointing and your in fairly smooth water, trim your mainsheet so that the telltail on the top batten is stalled about half the time, flys, curls back flys again (you get the drift) If the seas are up a little and you need to point but you also need the power to punch thru the waves ease the mainsheet and let the top batten open up until the telltail is streamming all the time. When you are close reaching use this setting and apply the boom vang to hold that sail shape before easing the mainsheet. This is all basic stuff and lots of tweaks can be added but this will get you 95% decent sailtrim.
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Old 23-03-2013, 23:03   #19
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Re: Sail Trim - True vs. Apparent Wind

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Originally Posted by robert sailor View Post
The top batten lined up with the boom is a good starting point. If you want super high pointing and your in fairly smooth water, trim your mainsheet so that the telltail on the top batten is stalled about half the time, flys, curls back flys again (you get the drift) If the seas are up a little and you need to point but you also need the power to punch thru the waves ease the mainsheet and let the top batten open up until the telltail is streamming all the time. When you are close reaching use this setting and apply the boom vang to hold that sail shape before easing the mainsheet. This is all basic stuff and lots of tweaks can be added but this will get you 95% decent sailtrim.
Actually, to shift back to lower gear in waves, you don't let out the sheet but instead you adjust the traveller a bit towards leeward
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Old 23-03-2013, 23:08   #20
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Re: Sail Trim - True vs. Apparent Wind

Depends on conditions, easing the traveller reduces your pointing and can also depower the sail. Keeping the boom centered and opening up the leach a little has been more common in my past years of racing but for cruisers either will do just fine.
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Old 23-03-2013, 23:12   #21
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Re: Sail Trim - True vs. Apparent Wind

Yes, the top batten parallel to the boom is a basic well known starting point for windward work. The several lower battens will be more closed. Their aft ends actually pointing a bit to windward. I think we are saying the same thing, but you have confused the words. Trimming the other way is surely impossible, no?

The apparent wind normally twists, lifts, with height. This tends to cause the sail to be trimmed with some twist as well. But it all depends on what you need to do to "get the job done."

OP: True wind is useless in sail trim. It is useful in weather reports and course planning.
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Old 23-03-2013, 23:15   #22
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Re: Sail Trim - True vs. Apparent Wind

Give you a point daddle, my choice of words was lacking. Yes the lower batten will be more closed than the top batten. Going to have to run these by my wife before I press send, its getting a little late for me,,nighty nite
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Old 24-03-2013, 00:04   #23
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Re: Sail Trim - True vs. Apparent Wind

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Originally Posted by robert sailor View Post
Maybe my English could be better or your eyes are wonky but when under the boom looking up the top batten should be in line with the boom. The other battens are not in line but proggresively are more open(away from the boom leeward)
My english might not be better than yours but you are right and wrong, you are wrong what comes to the top batten and right about the rest..
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