BoatBanter.com - View Single Post - Could a fan in front of a sail increase speed?

Brian Whatcott

On 23 Jul 2006 08:15:30 -0700, wrote:

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

Here's a known data point for you: a wind driven craft that can sail
directly up wind. Visualize the float which carries the diagonal
shaft, at the lower end of which is a small water prop, and at the
upper end of which is a bigger windmill. Models have been demonstrated
to sail directly up wind. Nothing experimental about it. You can
find pictures on the net.

Brian Whatcott Altus OK