Transportation: watercraft: sail
Rare In modern sailing, a water sail is any sail hung below a fore and aft rigged sail while running or dead before the wind. Generally a skipper won't pay to have a water sail built, but will instead set unused jibs or other staysails however they can be jury-rigged to catch a bit more breeze. There is some minor risk in the practice of having a breeze make up while you're running off and being unable to reef safely and easily. On the other hand, a broad boat bearing down on a hapless becalmed victim with everything including the skipper's drawers flying is a fearsome sight.
As a cultural thing, setting water sails is nearly unknown in the USA, and harks back to an earlier period of sail racing before WWII. It is not so much considered against the rules as gauche.
- Cunliffe, Tom; Hand, Reef, and Steer; Sheridan House, Inc © Tom Cunliffe 1992 ISBN 0-924486-40-6