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RGClark 07-21-2006 12:07 PM

Could a fan in front of a sailboat improve sailing?
Hello. Newbie here.
A question sometimes asked is that if you have a large fan 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 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.
Could this work?


kokopelli9 07-21-2006 12:21 PM

Is this another entertainment thread?

TrueBlue 07-21-2006 12:31 PM

Pirate's Booty 07-21-2006 12:35 PM

I recommend...
Just getting Surfesq to stand in place of the fan - he produces a much larger quantity of hot air!

kokopelli9 07-21-2006 12:40 PM

Good one PB...and so true!

DynaMeme 07-21-2006 12:57 PM

A fan, No, but...
For airplanes which have low speed performance requirements there is a concept called ventialted slots or blown flaps. In this case a blower, not a fan, blows air across the leading edge of the wing or flap. THis is done to insure the air flow stays attached -- preventing stalling -- and allowing the aircraft to fly much more slowly and land in shorter distances.

This concept has been experimented with on sailboats. Rigid sail catamrans in particular.

The issue is power requirements. Such a blower on a sailboat would have energy requirements that would be at least as demanding as a motorsailors.

However, boat's such as Cousteau's Alcyone did consider spinning their rigs using power until natural forces took over.

SailorMitch 07-21-2006 01:06 PM

Absent Ms. Booty's suggestion of Surfer One replacing the fan, yeah, sure -- having the fan blow towards the rear will work in theory. But boats are heavy so you'll need a BIG fan -- maybe an airplane engine with propellor or jet engine? Then you need a fuel source to run the engine, so add a huge fuel tank to the foredeck. Oh, a big battery for the engine also. Now all that will cause the boat to list to one side, so maybe put the fuel tank and batteries in a barge to tow behind the boat? But that will slow the boat down, so.......uummmmmm....... maybe just put all that money into some decent sails?

Denr-- is this really you?

RGClark 07-21-2006 01:09 PM

It is known with motorsailers that you can improve fuel efficiency by using the apparent wind on the sails created by the motor propelling the boat forward. The use of the sails also increases the speed you can achieve.
Using a propeller in the water is more efficient than using a fan in the air. However, some boats such as the fan-boats in the Florida everglades have to use fans because propellers in the water would get fouled by floating plants and branches in the water. Still, it is also true if you had a fan *at the stern* directed *rearward* and sails forward you could get better fuel efficiency and greater speed, just as with motorsailers. In this scenario though the fan is not blowing over the sails.
I'm asking a little different question. If instead you positioned the fan in front of the sails so it did blow rearward over the sails would you in fact get greater propulsion than what you would get from just using the apparent wind where the fan did not blow over the sails?


TrueBlue 07-21-2006 01:32 PM

Even without being an aerodynamic engineer, to me this notion seems half-crocked at least. But, assuming you were able to build such a high velocity fan, light enough to have little affect on boat trim & balance, but powerful enough to produce a force great enough, it perhaps is possible.

With that said, the orientation of the "fan" would be most effective if at a beam or close reach, and at a far enough distance from the sails to produce enough low pressure on the leeward side for forward propulsion. This is where your idea becomes a ridiculous fantasy.

PBzeer 07-21-2006 01:37 PM

Given the miniscule fuel usage of marine diesels on sailboats, you would lose more than you gained. For that kind of investment, the hybrid electric propulsion units now being worked on would be a much more efficent solution.

The only thing wrong with your solution Pirates Booty is, then you'd have to be looking at Tom Terrific all the time (shudder).

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