Can a water jet drive propulsion system be used on a sailboat?

Jet drives have been proposed for auxiliary propulsion for sailboats on and off since the 1930s, perhaps earlier. The chief advantage would be minimum drag under sail; no prop, no strut, no shaft. Some racers have even tried a closure flap over the flush inlet hole. This leaves an absolutely smooth hull when under sail. There is, though, no special advantage with regard to engine placement; the engine and drive shaft have to be located to connect to the impeller as directly as possible to minimize power losses. Using a pump that is separate from the engine wastes too much horsepower. Unfortunately, the laws of physics make jet drive extremely inefficient for boats that operate at less than 25 knots, and that includes all sailboats.