Was out sailing yesterday and before the race i was playing with the mast rotation on the shore and watching how it affects the shape of the sail and i may have a theory as to the increase in your speed. From playing around with the mast rotation, i noticed that the more rotation i induced, the flatter the bottom of the sail got, which makes sense, the fullness of the bottom part of the sail is dependent on the distance between the where the clue is on the boom (outhaul) and the tack at the mast. So if the outhaul remains fixed, and you rotate the mast, your pulling the tack away from clew, lengthening that distance and reducing the depth of the camber in the bottom of the sail, which flattens the bottom of the sail and will give you less drag upwind, meaning a higher potential top speed.

As i was sailing on a flat lake in moderate winds i was trying to get a fairly flat sail, and i found that by rotating the mast a little more than usual i could get more speed out of the boat, slower to accelerate but faster top speed. I tried to apply this to tacking, in that as i came out of a tack and moved forward i would derotate the mast to get a fuller sail to get some acceleration on faster, and as i built up speed i could rotate the mast and allow the boat to reach higher max speeds upwind, not too fast at actually getting into position and pulling all the lines nice and quickly yet, but i think with practice and consequently speed, it could make a big difference.

What ive read about mast rotation from books like Cat racing: for the 90s seems to support this as well, more rotation means a flatter sail, flatter sail means less drag, less drag means greater top speeds. Quoting the aforementioned book: "The rule of thumb upwind is: For the flattest possible sail, rotate to 90 degrees, for a fuller sail, rotate only until the trailing edge of the mast points to the side stay..."

Anyone else with concording or conflicting experiences/opinions?

Michael.