SailNet Community banner
  • SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!

Could a fan in front of a sailboat improve sailing?

29K views 181 replies 55 participants last post by  Matvolver 
#1 ·
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?

Bob
 
See less See more
#6 ·
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.
 
#7 ·
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?
 
#8 ·
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?


Bob
 
#9 ·
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.
 
#10 ·
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).
 
#11 ·
Assuming you could find a place to mount this fan-tasy, you'd only ever be able to go as fast as the breeze coming off the fan. So, in the doldrums, you might gain something, but the bow would clearly be dipping. In a breeze, the fan would actually serve to slow down the wind coming at the boat. Want proof? Put a fan in a windward window at home. You'll get good airflow when it's still outside, but if the breeze picks up, you're better off with no fan at all.

In all, newbie though I be, I'll stick to "natural" windpower.
 
#16 ·
A fan of a size required to move air in the volume required to fill the sails would generate some large decibels. Think or the sound of a yachts wind generator in a BLOW, and that is being driven not driving air.............LEAVE CIVILZED SOCIOTY IF YOU MUST!!, GET A STINKY, NOISEY, POLLUTING, ENVIROMENTALY UNFREINDLY MOTOR DRIVEN MONSTROSITY.
 
#17 ·
I have a better question... Can you lift yourself up by your bootstraps? What if you jump a little first to give yourself some momentum? :eek:

In all seriousness, the fan is going to act just like a propeller would in the water. It will give you some thrust if its big enough. You may even get a little extra from the sails, but no more than you would from equivalent thrust from a submerged propeller.

It's newton's third law of physics. Every action has an equal and opposite reaction. If there's thrust pushing the boat forward, its from the fan onto the sail and rig (pushing it equally backward). The fact that the boat moves forward because of the fan's thrust may draw a little extra air over the foil (sail) which will begin to cause some lift. But this isn't any different than if the 'fan' was underwater I would think.
 
#18 ·
To all you guys that speculate "if the fan was big enough" and other such speculations...wrong. ANY wind produced from an object on the boat (even from the hot air of surfesq) is subject to an equal and opposite effect in the opposite direction. I believe that was one the first laws of physics.
Pigslo
 
#126 ·
I have seen this thread on and off here now for several weeks and never really thought I wanted/needed/dared to step in. But is keeps getting bigger and bigger etc so curiosity got the better of me. No way would it get this far right? Wrong. Lol Pigslo said it best followed by the quantum generator. In my opinion dual polyquad synchronized phasers may work also IF we had a stable source of those dylithium crystals.
<O:p</O:p
Too freaking funny
 
#20 ·
RGClark said:
No, it is known by tacking into the wind the boat can have greater speed than the wind speed.

Bob
Bob,

Have you even tacked a sailboat?
 
#21 ·
kokopelli9 said:
Hey, SailorMitch...good to see you here again. How did the week sail with Denr go? Did you manage to get him sufficiently seasick?Kokopuff...
Hi Kokopuff!

Denr and I had a great week on the bay. Alas, he did not get sick -- the man has an iron constitution. But at least this time I didn't get sick!!!! My inner ear failed to grasp the intricacies of those Michi Gami square waves that first day back when. My home waters on the Chesapeake are kinder to my middle ear. Will send you more details in an email. Don't want to interupt the flow of this mesmerizing thread.
 
#23 ·
I can't believe you're actually asking this. This has nothing to do with sailing. That's just a stupid question. I'm amazed that you can use a computer. A simple understanding of effort and resistance is taught in grade 10. Maybe you should drop in. I know I'm no rocket scientist but this is rediculous. Thanks anthony for the bootstrap line. I'll have to remember that/
 
#24 ·
SailorMitch said:
Bob,

Have you even tacked a sailboat?
No, I'm going by what I've read about tacking into the wind:

The physics of sailing.
"How can boats sail faster than the wind? Lots of boats can---especially the eighteen footer skiffs on Sydney Harbour. Ask a sailor how, and he'll say "These boats are so fast that they make their own wind", which is actually true. Ask a physicist, and she'll say that it's just a question of vectors and relative velocities."
...
"The faster that the boat goes, the greater the relative wind, the more force there is on the sails, so the greater the force dragging the boat forwards. So the boat accelerates until the drag from the water balances the forward component of the force from the sails."
...
"Why are eighteen footers always sailing upwind?
In a fast boat, there's no point going straight downwind: you can never go faster than the wind. So you travel at an angle. But if your boat is fast enough, then the relative wind always seems to be coming mainly from ahead of you, as these arrows show. So the eighteen footers never set ordinary spinnakers: they have asymmetrical sails that they can set even when they are travelling at small angles to the apparent wind."
http://www.phys.unsw.edu.au/~jw/sailing.html

I gather from this that being able to sail at a speed faster than the wind speed is not the norm for the average sailboat, but only for boats especially designed for speed.
The method of tacking into the wind also works with ice sailing where the runners pushing sideways against the ice is what causes a force on the boat with a forward component that allows the ice boat to move at an angle *into* the wind. With ice boats the speeds can exceed more than 70 mph when tacking into the wind, much higher than the wind speed:

Ice Yachting.
"A course of 20 miles with many turns has been sailed on the Hudson in less than 48 minutes, the record for a measured mile with flying start being at the rate of about 72 miles an hour. In a high wind, however, ice yachts often move at the rate of 85 and even 90 miles an hour.
"Several of the laws of ice navigation seem marvelous to the uninitiated. Commodore Irving Grinnell, who has made a scientific study of the sport, says: The two marked peculiarities of ice yachting which cause it to differ materially from yachting on the sea are the ability to sail faster than the wind and that sheets are flat aft under all circumstances. Mr. H. A. Buck, in the Badminton Library, Skating, Curling, Tobogganing, thus explains these paradoxes. An iceboat sails faster than the wind because she invariably sails at some angle to it. The momentum is increased by every puff of wind striking the sails obliquely, until it is finally equaled by the increase of friction engendered. Thus the continued bursts of wind against the sails cause a greater accumulation of speed in the ice yacht than is possessed by the wind itself. When the boat sails directly before the wind she is, like a balloon, at its mercy, and thus does not sail faster than the wind. The ice yacht always sails with its sheets flat aft, because the greater speed of the boat changes the angle at which the wind strikes the sail from that at which it would strike if the yacht were stationary to such a degree that, in whatever direction the yacht is sailing, the result is always the same as if the yacht were close-hauled to the wind. It follows that the yacht is actually overhauling the wind, and her canvas shivers as if in the wind's eye. When eased off her momentum becomes less and less until it drops to the velocity of the wind, when she can readily be stopped by being spun round and brought head to the wind."
http://en.wikipedia.org/wiki/Ice_sailing

Apparently, these experts on ice sailing were not aware some sailboats can sail faster than the wind since that is not the usually state of affairs with the average sailboat. The greater drag of the keel in water explains why ice yachts are able to achieve higher speeds than sailboats.

Bob
 
#26 ·
anthonycolfelt said:
I have a better question... Can you lift yourself up by your bootstraps? What if you jump a little first to give yourself some momentum? :eek:

In all seriousness, the fan is going to act just like a propeller would in the water. It will give you some thrust if its big enough. You may even get a little extra from the sails, but no more than you would from equivalent thrust from a submerged propeller.

It's newton's third law of physics. Every action has an equal and opposite reaction. If there's thrust pushing the boat forward, its from the fan onto the sail and rig (pushing it equally backward). The fact that the boat moves forward because of the fan's thrust may draw a little extra air over the foil (sail) which will begin to cause some lift. But this isn't any different than if the 'fan' was underwater I would think.
I agree as far as trying to get the greatest efficiency from the power produced from an engine you very likely would be better off putting that propeller in the water rather than the air.
However, it is known you can get higher speed and higher efficiency with a propeller in water driven boat if in addition you use sails. You are in effect "pulling yourself up by your own bootstraps" since the apparent wind acting on the sails is coming from the power of the motor, which nevertheless acts to produce greater speed than from the propeller acting alone.

Bob
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top