Terry Spragg wrote:

Could a retractable shroud be allowed to slide down a prop shaft to fair
a stalled prop? How could it be reliably retracted to allow the prop to
be used after a voyage spent growing barnacles? Perhaps the shroud could
retract up into the hull with the prop stopped in a certain position?

Couldn't the acceleration of water created by venturi effect of a
properly designed shroud eliminate or at least reduce the induced drag
characteristic of a free-wheeling prop under the "load" of recharging?