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Old 10-03-2014, 21:40   #1
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Trimming the Main....

Lot's of pundits out there suggest trimming the main with the top batten parallel to the boom. Some adjust that to trim the second batten on a four batten main parallel to the boom.

My observation has been that trimming the second batten parallel with a 4 batten main creates more twist in the top of the sail than trimming the top batten parallel whether it be a 3 batten or 4 batten main so why suggest it?

What say you?
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Old 10-03-2014, 22:21   #2
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Re: Trimming the main....

Because there is wind shear between top and bottom of the main, the optimum angle of attack requires some twist in the sail. The amount varies with lots of factors, including sail design, boat design, specific details of wind flow at the time, color of skippers eyes and so on.

Thus, there may well be times when the top batten is the key, and others when the second one is better. Knowing all these things is what makes a really good sailor/trimmer. Wish I could do it consistently!

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Old 10-03-2014, 22:30   #3
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Re: Trimming the main....

The only time I've seen the top batten parallel to the boom, there was no wind. I trimmed the main until there was no (or very little) luffing the main unless needing to "depower." Trimming the jib and steering relative to the wind were also major factors affecting mainsail trim.
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Old 10-03-2014, 22:43   #4
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Re: Trimming the main....

The knot meter is your friend when trimming.
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Old 10-03-2014, 22:55   #5
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Re: Trimming the main....

Notice the unparallel-to-boom battens:

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Old 10-03-2014, 23:05   #6
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Re: Trimming the main....

Quote:
Originally Posted by jackdale View Post
The knot meter is your friend when trimming.
I trusted/relied on the look of the sails, the wool threads, showing apparent wind, and the "seat of my pants" (how the boat behaved). The speedometer was the last thing.
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Old 10-03-2014, 23:07   #7
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Re: Trimming the main....

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Originally Posted by markpierce View Post
Notice the unparallel-to-boom battens:

Doesn't count when you're overpowered and twisting off the sail to depower up high where the sail has the most lever arm.


Upwind the leech telltale 2/3rds or more up the sail is my indicator. Of course as mentioned above the knotmeter has the final word.

On reaches I try to get the telltales near the luff to all fly.

Battens parallel stuff is first approximation to get you close.
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Old 10-03-2014, 23:55   #8
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Re: Trimming the main....

I reckon a good method, (more situation specific than the "top batten parallel" rule of thumb), particularly going upwind

[when not overpressed and trying to stand the boat up],

is to trim the twist so that the top streamer (attached to the leech, level with the top batten) flies (rather than flops or curls to leeward) about 70-80% of the time.

Having (of course) first coarse-trimmed the angle of attack so that the remaining telltales all fly at least 95% of the time.
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Old 11-03-2014, 00:01   #9
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Re: Trimming the main....

I'd go with Andrew.

Why not using the telltales attached to the leech of the sail? I'd normally trim it so that they are all flying, except the top one (that one is difficult to fly and I think also shouldn't really fly because the low pressure area to leeward makes the air move up over the top. So the topmost telltale is not reliable)

Then when doing this, adjust your draught so that you have just a tiny bit of luff every now and then, and in theory this should be the fastest.

And: In light winds have more twist, in strong wind have less twist unless you want to depower the sail.
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Old 11-03-2014, 00:49   #10
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Re: Trimming the main....

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I'd go with Andrew.

Why not using the telltales attached to the leech of the sail? I'd normally trim it so that they are all flying, except the top one (that one is difficult to fly and I think also shouldn't really fly because the low pressure area to leeward makes the air move up over the top. So the topmost telltale is not reliable)

Then when doing this, adjust your draught so that you have just a tiny bit of luff every now and then, and in theory this should be the fastest.

And: In light winds have more twist, in strong wind have less twist unless you want to depower the sail.
Top one is the most important (unless you have it too close to the head of the sail), it's the one that tells you have the twist right.

Since the leech telltales don't indicate luffing, I run my top telltale stalled about as much as Troup does.
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Old 11-03-2014, 01:24   #11
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Re: Trimming the main....

The other advice will get you going. When you wish to fall off the wind in cruise mode and go on a reach simply pull the vang snug and easy out the main sheet, that will keep the proper twist in the sail.
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Old 11-03-2014, 09:37   #12
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Re: Trimming the main....

Many thanks to all who have posted answers to my question.

In hindsight I probably should have said people suggest top batten parallel to the boom as "a starting point" from which you adjust for twist later as conditions change.

My question was really about those who suggest starting with the 2nd batten on a 4 batten main parallel to the boom rather than the top one.

Going that far down the leech creates inherently more twist at the top of the sail initially. Just wondering what the reasoning was for adding that qualification rather than just sticking with the basic standard of "start with the top batten..."
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Old 11-03-2014, 09:44   #13
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Re: Trimming the main....

Quote:
Originally Posted by jackdale View Post
The knot meter is your friend when trimming.

That is how I do it . I don't worry too much about theory and focus on results (I do try to remember the lessons learned each time).
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Old 11-03-2014, 10:33   #14
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Re: Trimming the main....

The knot meter might be your friend on a lake but in the ocean its not as effective in making subtle trim changes. If your going upwind, ie: beating then go to the old rule of thumb of the top batten being parallel with the boom and the boom centered a midships. Look for the tell tails to all be streaming and the top one stalling about half the time. You can power up in lighter air or lumpy seas by easing the main and allowing a little more twist in it and easing the traveler down a little. There is so much more than this to proper mainsail trim depending on conditions but its a good starting point plus if your cruising then all you need is the basics anyways.
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