Boatspeed Tuning

by Mark Reynolds

From the Snipe Bulletin, March, 1981

Originally published in the North Sails Snipe News Letter

Most of us use the race course to test new sails or tuning adjustments. We put up a new sail or change our shrouds and then go out and use it on the race course. Usually, if we win the race, we figure we were fast and if we lost, we were probably slow. We may not, in fact, have won or lost because of boatspeed, but were tactically smart that day or unfortunate to be out of phase with the shifts. The best way to test new equipment, or tune, is with straight line two boat testing. A testing program allows you to isolate variables in order to see what is fast or slow in adjustment or sails. We can make small changes in a controlled situation to leap frog our boat speed to a higher level.

Here at North Sails we are constantly two-boat testing to insure that our sails remain the fastest available. Small changes are made in existing models or a completely new design may be tested. You can use this same process to increase your boatspeed. Not only sails can be tested but changes in other factors, such as mast bend, sheet tension and jib leads. When boatspeed testing, it is best to use only two boats. It is possible to use more but this can become harder to keep organized. It is best to test in an area that is as force of shifts as possible. The two boats line up with approximately 1 1/2 boat lengths between them and the leeward boat even with the windward boat.

The leeward boat usually has a little advantage because it is able to foot off without worrying about bad air, so it is best to alternate positions in case one boat is a pointer and the other a footer. The distance between the boats should not be too great so the boats will remain in the same wind. When ever one boat pulls out ahead or drops too far to leeward, stop and start over again. You learn nothing with one boat dead ahead of the other. Always keep an eye on the compass to make sure you can account for shifts which will favor one boat or the other. When testing, first make a few control runs with your standard trim so you can measure the change in speed. Change only one thing at a time.

When sail testing we try to have identical crew weight, masts, hulls and tune. This way we are able to isolate the variables. Boat "A" and "B' will start with the same sails. If the speed is not equal at this point we will switch helmsmen to see if this makes a difference. When we have both boats going the same speed, we have one boat put up the new sail. After we have measured a difference, we will switch sails between boats to see if we get the same result. When testing tuning changes let one boat (the faster if there is a difference) remain constant while the other changes their tune.

Keep track of all changes made, wind and water conditions and any other variables so the experiment can be tried again in different conditions at a later date to see if the conclusion is the same. When testing sails, we must test in every wind condition before an experimental model is tested on the race course and becomes a standard model.

Variables to experiment with: sails main and jib; mast bend - shrouds, spreaders, pullers; jib leads-fore and aft or in and out; main traveller adjustment; rake; mainsheet and jib sheet tension.

Everyone sails with different styles, crew weights and abilities, so everyone cannot sail with the same trim. Copying the set up of the fleet champion may not be the answer for you if you sail 5 pounds heavier. Two-boat testing will allow you to arrive at the optimum trim you need.

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