wrote:
Joe wrote:
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?



Yes it works!
I'm in the process of mounting this fan on my bow pulpit.
Making the swivel braket is the hardest part, air flow entry angle is
important.
I hope to gain 13kts:
http://www.superiorairparts.com/Wall...er1024x768.jpg

Joe



Have you performed any tests that lead you to believe the speed can be
greater than by putting the fan at the stern?
That is, will the fan in the front blowing over the sails increase
speed more than when it is at the rear and not blowing over the sails?


Bob Clark

Here's another way to look at the scenario. Suppose you had your giant
fan on a raft with no sail or keel. This raft is connected to the
sailboat by a rope. Suppose this rope initially is slack. You turn on
the fan directed towards the sailboat. The wind produced by the fan
allows the sailboat to move forwards by tacking into the wind. The raft
and fan also move forwards separately due to the momentum thrust of the
fan. The instant the rope is about to become taut you turn off the fan.
When the rope tightens, the sailboat will get a higher speed because of
the forward momentum of the raft. The raft will also be pulled backward
but it won't affect the forward speed of the boat as long as it does
not contact the boat. You make the rope long enough so this doesn't
happen. Once the rope is slack again. You turn on the fan again. The
process repeats.
You see the result will be that the sailboat will wind up having a
speed due to *both* the wind produced by the fan acting on the sails
and from the momentum thrust produced by the fan.


Bob Clark