Sailing ship power

[sally-anne]

I often wondered why it has not been possible to design a sailing ship to move not by the sails catching the wind but by rotating the propellers by wind power.

[Loosehead]

It is possible but there's no reason to do it. All the machinery in between the wind and the final propeller means that most of the wind energy would be lost in transmission so much more wind would be needed. In low winds the ship would not move. Probably work in high winds but the whole thing isn't viable. Sailing boats already use the most efficient system of converting wind into motion, ie the sail!

[Birt]

There are some odd designs of sails though. ONe is a solid "wing" much like an aircraft wing

[sally-anne]

Thanks but isn't there directional restrictions depending on which way the wind is blowing. A wind turbine could either charge a set of batteries to drive the motor or, with the intervention of suitable gears, run the propellers directly.

[Loosehead]

Sailing into the wind is done by tacking at an angle so there's no need. I'm sure marine engineers have looked into the windmill idea in the past, there may even be boats that do it, I've never heard of one though!

[Joeloki]

Sally-anne is to be congratulated upon posting a very thoughtful question - just as Loosehead (a misnomer surely!) has given a commonsense answer. Now I'll contrast all this commonsense against my daft comments!

Why not design a cylindrical windmill to rotate about a vertical axis. This might directly drive a generator which, in turn, could be coupled to a motor-driven propeller. The system might serve no more than to supplement the power provided by a diesel-generator - but it would help. The advantage of a 'cylindrical windmill' is that the ship could just as happily sail into the wind as it could in any other direction.

Snags? There are a few but I've no doubt you can see them for yourself.

[Birt]

I have actually seen a boat with a wind turbine on it. The harbour master said it was to power the boat but im not sure if this is true. I will look into it and get back to you if i find it.

[mibn2cweus]

Sailing Directly Into the Wind???

[Gef]

birt, you see many boats, especially canalboats, with wind turbines on them. They are used to keep the batteries charged when the boat is not in use.

[sally-anne]

Thanks Gef. Why cannot the battery use be for a motor to rotate the propellers. I have seen truck drivers use powerful cookers in their parked cabs. They have to be powered by batteries. Surely these high capacity batteries be charged by wind turbines and rigged to provide the power needed.

[brachiopod]

There is a good reason you don't see rotors on sailing craft. I shall try to explain by example and analogy!

You have a propeller driven sailing boat that is highly efficient - so there is little energy loss between the wind received and the motion provided by the propellers.
You have a wind from astern blowing at 10 knots (ie from behind you). Your wind turbine-affair converts this to forward motion through the propellers.
What happens when you reach a forward speed of 10 knots? You effectively have no wind, as the relative wind speed on your turbines is zero, as you will be moving at the same speed, and in the same direction as the wind.

In real life, this is why helicopters do not travel at the same speeds as fixed-wing aircraft (many hundreds of miles an hour).
The spinning rotors of a helicopter create lift, but no forward motion, so a helicopter moves forward by 'pitching' its nose down slightly , so that the direction of lift is slightly forward, resulting in forward motion relative to the ground.
There is a limit to the speed a helicopter can achieve, since the forward motion itself reduces the relative air speed of the rotors, and hence the amount of 'lift' they generate.

[liamjford]

I remember seeing a picture of sucha boat in a magazine some years ago. As stated above, sailing into a head wind was impossible.

This used large batteries and an electric motor.

At the moment a sail is the best way to get enrgy out of the wind, cheaply and effectively.

I have seen a parasail (similar to a paraglider or kite surfing kite) for use with engined ships as an additional form of free energy, to increase speed and reduce fuel use.

http://skysails.info/index.php?id=111
http://www.pgforum.com/viewtopic.php?t=1412&hi ghlight=tanker

Some info on electric yachts and a wind turbine powered one here: http://en.wikipedia.org/wiki/Electric_boat

[sally-anne]

Thanks Brachiopod. If the wind turbine was in the form of horizontal rotation with cups similar to the device that measures wind speed, it should not matter what direction the wind is blowing or the speed the boat is moving. Theoretically when the wind speed from the back and the speed of motion is the same the turbine should stop but in reality the momentum will continue the motion gradually slowing to cause a difference in wind speed and start rotating again.

[Birt]

Gef

As a boat owner i understand that many boats have turbines to charge batteries etc. The boat i have seen was not like this. The turbine was the biggest part of the boat. I can only imagine it is a "prospecting Ship" for off shore wind power farms. Cant find an image of it anywhere though. Was very unusual.