Jib trimming line

[Chris Rogers]

I have two different books written about sailboat racing. I have noticed that one book says to trim the jib to a line 10.5 degrees from the centerline of the boat, and the other book says it should be trimmed 18 degrees off the centerline. What gives? Should it vary from boat to boat...if so both of these guys are wrong. Thanks for the help.

[Wiley Baggins]

Originally posted by Chris Rogers:
Should it vary from boat to boat...Yes, and the cut of the sails will affect sheeting angles as well. What sort of boat do you have? If it is a one design, there is undoubtedly a "hot set-up" (maybe more than one). I'd look at other boats in the class, if possible.

[John E Hardiman]

Little question, big answer. If I (or anybody) could answer that question I (or they) would be rich by now. :D

The Theory: At any given time, a jib should be trimmed to provide a slot that generates maximum velocity over the lee of the mainsail without stalling it so as to generate lift. The six major controlling conditions are true wind velocity, boat velocity including leeway, heel angle, and jib size and overlap. To do this there are four major adjustments (sail draft being built in is the fourth); headstay tension, leech tension, and clew position. Now clew position and leech tension can be inseparably linked or not given the sheeting arrangement. It would be best to have them separate controls. Now, as we have seen that there are 10 major factors to just bound this problem, that anyone says that there is an optimum sheeting angle for all sailboats is just plain bumph!!

The Reality: In order to give yourself the maximum adjustment to the jib, you should have the ability to set the clew anywhere. With class and or other rules this is generally not possible. Additionally, the jib track/block can only fit on the deck and has to dodge all the other things that compete for deck space. Some high-end setups use multiple tracks with cross tracks, or split jib sheets with barberhaulers or twings. Some people club the foot (this works with the non-lapping jibs only). But most just use an inner and outer track with adjustable cars. For this general setup the inner track should be at an angle of 7-10 degrees (so that a positive AOA is maintained during pitching/rolling) from the Centerline with the vertex at the jib tack. This will most likely pass inside the shrouds and is only suitable for minimally lapping sails. The outer track generally follows the deck edge aft of the shrouds. Of course, these locations are dependent on deck arrangements. Now, however, the problem becomes that in order to position the clew, you have to change the leech tension. Therefore, with the normal track and car jib sheet setup, you may not be able to achieve the one "optimum" point for a given sail/wind/boatspeed/heel/headstay tension.

Now, those authors you cited may have been writing to very specific audiences. The optimum jib sheeting angle on a flat carbon-fiber scrim sailed catamaran is very different than a "wet snail crab crushing" double ender with baggy Egyptian cotton.

[SailBoatDude]

Read the tell-tails on your headsail. It's the easiest and fastest way to find a good sheeting angle for the wind strength, sail cut, rig tension, etc.

In fact, the little cheat sheet that comes with new sets of tell-tails will tell you much about what to look for in the trimming of your sails.