Join Date: Nov 2007
Location: SF Bay area
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I don't understand why having a higher clew necessarily reduces sail area. It depends on what direction the clew moves.
If the clew moves straight up, i.e., gets closer to the luff, then yes, the sail area will be reduced. Similarly, if you take a deck-sweeping headsail and move the clew up the leach of the sail, then cut off the cloth below, area will obviously be lost.
On the other hand, if the clew is moved up and aft, parallel to the luff---in other words, the sail is skewed upwards---the sail area should remain constant.
Proof: imagine cutting the sail into strips parallel to the luff. Shift each strip up by an amount proportional to its distance from the luff. Resew where the strips meet. You have a new sail with a higher clew and the same area (pretending for a second that you haven't destroyed the camber).
It's easy to see how this applies to a flat-cut jib, but in general, skew transforms preserve area. Sail area is roughly equal to luff x LP / 2.
I don't have any idea how a high-clew headsail is geometrically different from its low-clew counterpart, though. But I also don't see any reason not to have the clew of a high-clew sail farther aft, other than interference from the mast when tacking, which is a problem with low-clewed headsails anyway.
s/v Laelia - 1978 Pearson 365 ketch