NotWal said...
I think its about providing a smooth transition for the wind from the high pressure at the load area to ambient pressure as it leaves the sail.
Old fashioned sails created a heap of turbulence at the top particularly when the sail deformed under load.
To avoid the hook the sail has to be flat at the top in the minimum loading condition. When its further downhauled for strong wind it has more flat area at the tip than it needs. Even though you may be carrying more area than you need the drag accruing to it is much less than the alternative of a hooky turbulent tip.
If I recall correctly it was Bruce Peterson who discovered the significance of a twisty unloaded tip when he was working for Gaastra. He was out in the test rig, a van with the facility to mount a sail on the top and load cells to detect the lift developed. The van was stopped with a test sail mounted. The wind was blowing and he poked the tip of the sail with a stick and watched the lift reading go up.
Don't use a smaller fin. Nothing you do to the air has any effect on the lateral resistance in the water.
I may be off the mark but I hate big brands taking a previous idea and saying it is their own brain child. There is way too much of that these days.
I remember Midget Farrell espousing the virtues of a flexible sail head for wavesailing in the early eighties (when the current trend was for tall, thin, stiff sails) and using them himself. This predates the current modern sails by 20 odd years. I am guessing Bruce Peterson made his discovery 15 odd years ago?
I had a photo of him on the south coast using one of his "twisting head" sails.
