Close×

Sail Trim

Mark Reynolds of Quantum explains how to test sails and set-up.

A well-organized, two-boat testing program is the best way to make advances in boat speed. Trying to determine speed differences on the racecourse can sometimes be difficult because there are so many variables. Testing and tuning is much more fruitful in a controlled environment away from racing tactics, other boats and lay lines. Much more can be done in less time. You can also test tuning techniques such as sail adjustments, body positions or spars.

When testing, you want to reduce as many variables as possible. Wherever possible, use the same boat manufacturer and crew weight for both boats. If possible, use a rubber boat with an observer equipped with camera gear for recording sail shape, mast bend and boat trim. We use a digital camera – often in a waterproof housing – on both the sailboat and the chase boat. It is very easy to observe side mast bend from photos taken from straight behind the boat by turning the prints on edge and sighting up the mast. The sail photos allow you to measure the shapes and evaluate the differences. You can measure on-board photos on your computer using specialised programs, which eliminates guesswork. If you re-cut the sail you can see exactly how the shape changes. It also provides you with a record for look-back.

The location is also important when testing. Pick a location with steady wind. If possible, get away from the shore to get winds as steady as possible. About two boat lengths should separate the boats. It is best to have the leeward boat a little in front of the windward boat. In the Star, for example, the boats should be lined up so that the windward boat’s helmsman can sight straight across the stern of the leeward boat. This rule of thumb should work in most boats. As soon as one boat moves more than a boat length ahead, or the gap between boats is greater than three boat lengths, then you should line up again. This is the biggest mistake most people make. It is very important to get lined up again because otherwise it gets more difficult for the guy behind, and you both will end up wasting time.

It’s often tempting to make more than one change at a time in an effort to increase speed. But this makes it difficult to determine the real reason for the speed change, which hampers a true analysis of cause and effect. Be patient.

It’s best to start out with the same sail on both boats until each boat gets tuned up and going at the same speed. While the sails on one boat stay constant all day, the sail(s) are changed on the second or “test” boat. Toward the end of the day, you may want to put the original sails back up on the test boat to confirm it has the same speed it had at the beginning of the day.

It’s a good idea to start out with the standard tune and sails and then start making predetermined changes on the test boat. The difference between fast and average sails is usually so small it takes a while to figure out. Often a sail, especially a main, will initially test slow but go faster after a bit of rig adjustment. It’s a good idea to have two-way radios on each boat. That way if one boat needs or wants to try an adjustment, the other boat can be notified.

When you are testing sails, the same boat should stay to windward and the other to leeward; this will eliminate one variable. If you are testing the tuning you may want to switch positions every once in awhile to confirm if your results are due to the fact that wind shifts or pressure favour one side or the other.

Throughout testing, it is important to record all your settings and keep clear notes about the conditions, your observations and the results. Keep your photos with this information for a complete record of your sail testing. It takes a little effort, but when done well, two-boat testing is the best way to increase your speed in a way that is repeatable for more consistent results.


Mark Reynolds is a Star class sailor and American Olympic champion. He began sailing Stars at age four, training with his father who crewed with Dennis Conner to claim the 1971 World Championship. Reynolds has competed in multiple Olympics, winning medals in 1988 and 1992. In 1996 he finished eighth. Afterwards he formed a new partnership with crewman Magnus Liljedahl, and they went on to win a string of championships, culminating with a gold medal at the 2000 Olympics. In 2000, Reynolds was named IASF/Sperry World Sailor of the Year and in 2001, Rolex Sailor of the Year. Reynolds is owner of the Quantum San Diego loft where he makes the sails for most of the boats competing in the Star class.

comments powered by Disqus