Could a fan in front of a sail increase speed?

[RGClark]

Hello, newbie here.
A question sometimes asked is that if you have a large fan at the stern on a
sailboat blowing forward into the sails would that propel the boat
forward? The usual answer given is no because the fan blowing air
forward would produce momentum propelling the boat backwards. This
would swamp the effect of an effective wind acting on the sails.
But suppose instead you had the fan in front blowing rearward into the sails?
In this case the momentum would propel the boat forward. Furthermore by
using the method of tacking into the wind, the wind blowing into the
sails could produce a force with a forward component as well. Then the
acceleration forward should be higher than that produced by the
momentum flow of the fan alone. The speed could also be higher than the
speed of the air created by the fan since tacking into the wind can give you a higher speed than the wind speed.
Would this work?


Bob

[Richard Hillsid]

Definitely. except when going downwind you would have the fan blowing the wrong way.

Going up wind I was wondering if you could come up with a gear box so you could have a slow turning minimal resistance propeller in the water that is coupled to power the fan.
There would be some extra drag but if the aft blowing fan is powerful enough it should overcome the resistance easily as the sails are helping with more power available do to the fan and the momentum it gives, the acceleration could be slow but steady, with maybe a new speed record in mind once it gets up to speed, there should be some means of regulating the speed, maybe a brake or sea anchor used when needed not to over stress the hull.

[safewalrus]

Why would you want to?

If your generating energy to make your fan work (which of course you would be - or a long lead?) why not put it straight into a more efficient propeller? Why re invent the wheel?

[frosh]

There is already a thread from a few months ago that looks at various unconventional ways of increasing sailboat speed. The fan idea has already been suggested as well as quite a few you never thought of!
http://boatdesign.net/forums/showthread.php?t=11162