At altitude I have always believed that there was 'less air in the air.' The thinking was based on the relative density of air at altitude, which is less. Therefore, the force provided by the moving air (wind) would be proportionately less than an equal windspeed at sea level.
I discovered this phenomonon for the first time at the 1994 US Nationals at Dillon, Colorado. During the Western Regionals, which preceded the US Nationals skipper Pat Crump and I set our boat up and sailed without checking the rake. We won the regatta, but checked our rake before the Nationals. We were at 22'11.5", which was much higher than the rake should have been for the shifty 8-10 knots of trapezing breeze we had. We raked back the rig and sailed the Nationals at 22'8" and immediately had pointing problems. Why could this be?
At the 1998 Nationals I learned from the experience and set up with 3" more rake for each breeze setting and sailed between 22'8" and 22'11". Again in the light breeze, we won the regatta. We had higher pointing and better speed than the majority of the fleet.
A week later we tried the same technique at Huntington Lake, and it paid off. In the light and meduim breeze we carried 22'10" and 22'11" of rake and had height and speed on the fleet. The added rake was added power, and even though the breeze climbed towards 14 knots in the afternoons we were able to depower the boat very slightly with the cunningham and balance the helm. Higher rake at altitude became our rule.
In addition to rake, we used our strut up constantly in the light air (below 6 knots.) Because the air has less force, it needs a flatter sail so not to disturb the airflow. Our overbent mast looked strange in light air, but the results were quite good. Again our pointing and speed increased. While we use some strut up at sea level, it is usually spared for the extremely light breeze, 3 knots or less. As soo n as the boat is drawing air consistently we will bring the mast back to neutral. However, at altitude it consistently paid to leave the strut up on until the crew joined the helm on the windward tankside.
Our last great lesson was to pump the sails and rock the boat much less in the lighter air, sudden movements tended to knock the air out of the sails and limit pointing. In addition, we kept our boat dead flat, not like the 5-8 dergees heel most boats were carrying. Heeling the boat in light air is a farce in all but a drifter. Instead, we concentrated on keeping our weight forward in the boat to get the transom to break clear of the water. We would hold this technique, with the crew crouching on the wire and the skipper right forward against the windward shroud until about 8 knots (when the boat stands a chance of planing) when I would slide aft to the thwart, bringing the transom down lightly on the surface. On runs especially, we would maximize our weight forward to clear the transom. On out tricky boat we even had the abillity to rake the mast forward on the run, which proved to provide lower angles and higher speeds.
Next time you head for the mountains to race you Fireball remember, there is not as much air in the air-and set up accordingly!
North Sails South Carolina