Wednesday, November 02, 2005

The First Leg | Trim for One

The most important trim concept with a main and jib is to think of the two sails as one large airfoil. The overall shape of the two combined sails defines the lift and speed that the boat will have. Trimming should follow a sequence with the main trimmed first to balance the helm. The mainsheet and traveller should be the primary controls in lighter winds, and as wind builds adjust the outhaul first until the draft is 30-40% aft of the luff (the power pocket), then begin adjusting the boom vang to flatten or close the leech. Once the wind builds to the point where all available bodies are on the rail, use the backstay adjustment to open the leech.

After every adjustment, re-check the overall trim again. It is usually necessary to adjust the jib once you have properly shaped the main for overall foil shape. The slot or groove of the foil should be even all the way up. If it is uneven the airflow will not be optimal.

The jib draft (power pocket) is adjusted by moving the cars forward and back. One thing I will be doing this year is drilling holes in the jib lead track in between the factory holes to fine tune adjustments on the jib.

Have been researching sail trim sites and will have a nice list compiled shortly. Some good resources out there. Look for them in the next post.

4 Comments:

Blogger EVK4 said...

What do you think of the North U trim guides? I'm taking up racing and am starting to worry more about fine tuning than I ever have in ocean miles (once went 72 hours without adjusting a sheet, must be some sort of record).

11:11 AM  
Blogger the skip said...

lol, that is a long time to go! Usually adjust trim (depending on winds) about once every 5 minutes, sometimes less. The J 24 is a very responsive boat and I find small inch increments make a large difference in speed and pointing. I have not read the North U guide in full format but it is written by Bill Gladstone, who has a number of great articles on the net (I will include some). Everything I have read from him to date has been extremely helpful.

I consider him an excellent source of information and guidance. So I suggest picking it up if you can. He also has a quick trim guide that might be helpful as well. Just putting together the next few posts on trim with some great links on it for overall shape and speed versus pointing, draft position etc. Hope these links help as well.

Great to hear you taking up racing! Keep me posted as to how you are doing. And I will help whatever way I can. Are you going white sail or flying the kite?

11:40 AM  
Blogger EVK4 said...

I only have white sails so I'm somewhat limited to that.

The 72 hours without trimming is somewhat misleading. We were crossing the Atlantic and the autopilot just kept us close-hauled while the wind shifted favorably for a few days. Three days without tacking, you tend to get lackluster when stowing things. The first tack could probably be heard the next ocean over!

6:35 PM  
Blogger the skip said...

I raced white sail for 5 years on a tanzer 26. Sluggish boat but a great skipper. Was in the pit and cut my teeth on trimming. We maintained the top spot for a few years, and pretty much finished in the top 3.

Nice to be able to cross the ocean....great lakes up here, no really big bathtubs to float around in!

You have pretty steady winds from what I gather too. Our winds because of lake effect tend to be really swirly and shifty. Can change 180deg in matter of minutes. Makes life interesting. Hope the articles I posted will help in some way.

6:57 AM  

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