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There is no magic formula except total concentration
Thoughts on Boatspeed by Jack Kelly
Jack Kelly was chairman of the class on two separate occasions, and won most of the Sigma trophies with Moonshine.

There are obviously many ways of losing time on the leaders, including getting the wrong side of a windshift or getting a spinnaker wrap. What we really want to think about, though, is the helmsman's ability to get his boat up to maximum speed and keep it there for the whole of the race. Many owners worry undult about the rig sit-up, but the better sailors in the class have many different approaches to setting up their rigs and there is no one "magic formula."

The one thing the top helmsmen have in common is the ability to concentrate totally on the job in hnad. They also tend to have a natural feel for when the boat is performing at its best. Most of us however do not have this natural skill, and we need to know how fast the boat is going. A well calibrated log is needed for this. There are several well-documented ways of calibrating a log, but the simplest uses a GPS giving course and speed over the ground.

Take the boat to an area where there is a known steady current flow (not during slack water, when current flow tends to be unpredictable). Motor the boat at a steady speed of say, six knots directly into the current. Ensure that the course over the ground (COG) is exactly the same as the heading. One the speed over the ground is established, it should be noted. It should be a slower speed of say, 4.8 knots.

Turn the boat through 180 degrees, at the same speed, and again note the SOG when it settles. It should be a higher speed, say 6.6 knots. The average of the two speeds (in this case 5.7 knots) can be taken as a true measure of the boat's speed through the water, and the log recalibrated to match this figure. Then repeat the whole procedure to confirm the calibration. This technique is much quicker than sailing a measured mile several times!

Having acquired an accurate log, the next thing is to use it to improve your performance by aiming to reach the optimum speed dependent on wind speed and angle at all times during the race. Each boat can make its own polar diagram, but fortunately we do have a set of figures for the Sigma 33 which are based on the potential of the hull shape and sail plan of the boat. With these numbers visible in the cockpit, it will soon become apparent if the boat is not sailing as fast as it could in the prevailing conditions. If you are sailing faster than expected, it may pay to sail a bit higher on the beat or lower on the run to achieve a better VMG.

True wind speed readings are necessary, as the apparent wind will vary depending on whether the boat is sailing upwind or downwind. Of course, if the boat gets on a wave, target speeds for running and reaching may easily be exceeded! When target speeds are consistently achieved, the settings for sail trim should be noted so that they can be reproduced. If target speed is consistenly exceeded, the chart may be modified of the log calibration rechecked!