The Wind Powered Sail-less Boat

Hello everyone,

I am an engineering student in the U.K. and have just been given a project to design and create a working model wind powered sail-less boat. Thats right a boat powered by the wind but without a sail. Ha ha...

Anyway a bit about the project.

The hull is approximately 1.5m x 0.4m (at widest section).
We have 2 hulls and can therefore construct a catamaran design. (likely)
It can hold about 20kg max per hull, without buoyancy aids.

The boat does not need to travel with any significant speed but must be able to complete a short slalom course and make it back to shore if the wind speed drops....therefore some form of energy storage must be implemented, although this comes with a hitch. It must be mechanical energy storage ie flywheel, elastic band or spring.

The contraints of the project allow the use of battery powered servos to ideally operate rudders but this is the only electrical storage permitted.

So far, our team has decided to use a vertical axis wind turbine, probably Darius, to provide the core power. This obviously has the advantages of being able to catch the wind in any direction and it's weight is more evenly distributed than a horizontal axis wind turbine, helping with balance issues.

This is probably the sort of turbine we will construct ourselves due to it's small scale nature and also operate with mechanical power transmission to attach/gear some form of mechanical storage device.

We have not yet constructed any part of our model boat as we are still in the early stages of the analysis. I have therefore made this post to generate some interest in the project and also run our initial ideas past everyone.

So what do you think? Is this possible?

Ha ha, let me know your thoughts!

Thanks,

Duncan

 

All of the most august sailing associations and racing governing associations have all agreed that kites are not sails.

 

The Darius rotor driving a suitable propeller is probably a good choice. It should have more than two blades to even out the power pulses. A catamaran hull will be more stable but not a lot of stability is needed with the Darius rotor. The catamaran will be much more difficult steering thru the slalom so a monohull with a keel may be better. A flywheel sounds like the simplest storage mechanism but gearing may be an issue to bring it up to speed.

It may be ruled illegal but a small generator-motor driving the flywheel is a simple way around the gearing problem and gets past the prohibition of electrical storage.

The Darius rotor is not self starting, so you have to get past that problem also.

A Savonius rotor is self starting but less efficient.

 

If you go with screw propulsion, a large diameter slow turning air screw might be more efficient for a low power boat than a water screw.

 

I am not an expert on vertical turbines, but from what little I know I would be very concerned about the system compared to a horizontly propeller for a number of reasons.

Depending on which vertical system you use, these are all significant problems...

Giromills - demand heavy towers which may cause boyancy and balance issues.

Cycloturbines - are very complex and have a lot of moving parts. Leading to corrosion problems, and put a lot of weight far off the centerline of the boat, exaserbating the rocking of the boat.

All of these also have a problem with pulsating forces, since the blades don't produce the same amount of force at any wind angle. Meaning the engine could go into an occillating destructive sequence (see the Tacoma's Narrows Bridge disaster).


I keep thinking that a horrizontly propeller while less flashy is a better design... Not to mention that is should be able to find parts much easier.

 

Not only can it be done, it has been done. The most common method is to have a horizontal axis wind turbine connected via a shaft to the propeller in the water.

A clutch and transmission could be used to couple and decouple with a flywheel for energy storage. The wind turbine could be coupled to the prop without the flywheel, or the wind turbine connected to the flywheel to spin it up, or the flywheel connected to the prop without the wind turbine to power the boat. Modern flywheels are competitive with batteries in terms of energy density. Naturally, any flywheel must be enclosed in a protective case to contain the shards if it should fail, and ideally it would be located so no people are in the plane of rotation.

Revelation II is one such boat.

Such a craft can sail straight into the wind. And, if it weren't for the high resistance of a hull in the water, it could also sail directly downwind, faster than the wind. Which has been demonstrated in practice on land, with the rotor connected to the wheels. When operating faster than the wind, it's actually the wheels that are turning the rotor, and the rotor propelling the craft!

This boat is an 1896 Bembridge Redwing hull fitted with an autogyro sail in 1933.

You might think it's the same sort of craft. But it's not. The rotor is not connected to anything - it just spins. It's a rotary sail, just like the unpowered rotor of an autogyro is a rotary wing.

Which should give you something to think about - you can use a horizontal axis wind turbine that way, but can you use a vertical axis wind turbine the same way?

And is it more efficient to use the rotor as a sail or to use it as a turbine to drive the prop? Does it depend on which way the boat is traveling or how fast it's traveling?

 

Video of Turbine boat

There's a video of another similar boat on Youtube.

 

Propulsion efficiency

Hi Duncan,

Just to suggest you to investigate the propulson efficiency of your underwater device.

As your boat will probably be relatively slow, You will probably need a big propeller in the water with low revolution.

There is an alternative solution for low speed.

Imagine a square/ rectangular box open at the front and back sides, just like a matches-box after pulling out the inside part.
This box is underwater and its open ends are in the direction of the water flow of course.

At about a third of its longitudinal axis you have a connection-rod which transmit a rotative motion (the windwill above the deck) into an alternative motion.

This connecting rod moves a flat plate inside the box, of course you have to adjust the box-thickness with "crank" stroke.

The flat plate moving inside the box will move quite similar to a dolphin tail, and the box will limit tip vortex.

My English is far from perfect, so if it seems confused to you, make a drawing of it, everything will be clear.

Regards

EK

 

No. Because VAWT mostly have heavy components low down, they do not need heavy towers. The "wings" of the VAWT can also be made of sailcloth so they can be very light.

Some have heavy parts, most do not. In most cases they are still lighter than HAWT with their heavy gearboxes and generators.
True, some are complex, as you say, but others are not.

Yes, that can be a problem, but it can be easily overcome if designed carefully. See, for example,

Variable pitch Darrieus water turbines
B.K. Kirke and L. Lazauskas,
J. Fluid Science and Tech., Vol. 3, No. 3, June 2008, pp. 430-438.
http://www.cyberiad.net/library/pdf/bkll_jfst_vol3_no3_2008.pdf

Although this paper is concerned with VAWT operating in water, the principles for reducing shaking are the same for wind turbines.

All the best,
Leo.

 

Don't forget wings. Here is an intersting site on the wing-sail concept:

http://www.ivorbittle.co.uk/The wing-sailed yacht for the web.htm

 

First Law of Thermodynamics

Tom, your aero/hydrodynamics is normally so good that I had to do a triple think before coming in with this, but directly down wind faster than the wind is not possible without violation of conservation of energy, on land or water.
If on a perfectly still day such a craft were given a push to get it moving, it would immediately have a headwind and could then accelerate smoothly to its destination. While the free transport sounds nice perpetual motion is a definite no-no.

My mental model for windpower is as follows (note that in this discussion I'm only considering the drive mechanism, eg sails or turbine+propeller, and am ignoring hull drag etc.):
For any sail or turbine 'drag work must be greater than thrust work'. Ideally: thrust=drag and we have 100% efficiency. To paraphrase: the energy we harvest by changing wind momentum over airfoils (thrust) is limited to equal or less than the work required to push our airfoils through the air (drag).

There is hope. Drag and thrust do not have to be applied in opposite directions. Drag acts with the direction of the wind. Depending on the type of sail or turbine we can make thrust act in whatever direction we like, typically in the direction we wish to travel.
However, when we point directly into the wind (or apparent wind, as for dead down wind faster than the wind) thrust and drag are in opposite directions, and as drag>thrust we end up going backwards.

There is, however, another factor that does allow a wind turbine powered craft to sail directly into a head wind, but this does *not* apply for sailing DDW faster than the wind.
Energy = work = force*distance. We know that drag work is greater than thrust work, but if we can get the thrust to be applied over a shorter distance than the drag then thrust force can be greater than drag force. Traveling directly upwind a craft obviously has a longer track through the air (air distance = time*(windspeed+craftspeed)) than its track over the ground (time*craftspeed). Therefore by applying the thrust in the water (or via the wheels for a land craft) a larger force than the air drag can be produced for the same or less energy, and so we can have forward motion.
By contrast if we were traveling DDW our track through the air is shorter than our track over the ground, so any force applied to water or wheels must be less than drag force.

 

Most people struggle with the concept of sailing directly into the wind. Very very few can understand how it is possible to sail directly down wind faster than the wind but it is possible. It does not violate any fundamental laws. It does however rely on relative movement of the air over the water. If there is no relative movement (no wind) then there is no go.

If you want to sail into the wind you extract power from the wind and deliver it to water. Providing the effective gearing between the AIR TURBINE and the WATER PROPELLER is such that the drag on the turbine is less than the thrust on the propeller it will go forward. With a 1:1 mechanical gearing the turbine pitch needs to be at around 1.7 the propeller pitch if you have an efficient design. If you have a higher loss system then the ratio is going to be 2 or even higher.

To sail directly downwind faster than the wind you extract power from the WATER TURBINE and deliver it to the AIR PROPELLER. So the boat can move faster than the airstream over the water with the propeller providing the thrust. Again it gets down to gearing with the water turbine having the larger pitch.

When you get into detail there is no real benefit in optimising a system to sail directly upwind AND directly downwind. The latter would be required so infrequently that it is not worth compromising the upwind ability. Simple solution is to just tack down wind still using the air turbine as the power collector.

Irrespective of the practicality it is not impossible. It does not violate any natural laws. Just hard for most people to think it through. Even conventional sailing boats can have a higher VMG directly down wind than the windspeed but they do not sail directly downwind to achieve it.

Rick W

 

Thanks Rick, that has cleared up my concern. I saw how the speed differential gave power to windward, but had a brain fart when it came to inverting to problem (extracting power from the water, driving the air rotor) for dead down wind.
I'm happy now, and agree it's possible

For most of us sailors tacking downwind is the easier option.

 

To get a turbine/propeller system to work well upwind is a design challenge. It needs to have efficient blades and these are inevitably cambered foils. Once you start looking at DDWFTTW then you also need efficient foils but they would have opposite camber. Also for the size of craft I have been looking at the air propeller needs to be much larger than the air turbine to get good results. So I conclude that these practicalities exclude combining the dual ability in a single system.

In fact I do not see much merit in the simple turbine/propeller system with a mechanical linkage. I believe if you treat the turbine as an energy collector, storing to a battery, and this then drives an electric motor you get a nice system. With this sort of system you can store excess power in strong winds rather than wasting it trying to push a hull much faster than it was designed to go. The boat just plods along at a a steady pace with the battery taking excess power when available and delivering more power when needed. You can also store power while sitting at anchor.

Rick W

 

Gearing for upwind or downwind

Hi Rick, can you elaborate on this and give and example?