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I recently read in a history book that sailing ships that really needed to go fast would pour water on their sails because "wet sails capture the wind better than dry sails."
Why might this be? Does it have to do with changing the friction properties of the air-cloth interface? Or does it help the sail hold a good shape against the wind by making it heavier?
Sails used to be made of relatively porous fabric which could not sustain pressure differences very efficiently. Getting them wet reduced the porosity and improved their performance.
With the introduction of synthetic materials in the 2nd half of the 20th century, the fabric porosity was almost completely eliminated and is no longer a factor.
