The Wind Powered Sail-less Boat

So why don't you demonstrate it then? I don't think anyone else in the world believes it is easier on water (have you thought about it?)

 

Well, if sailing downwind faster than the wind has "no merit" and sailing directly into the wind "does not make a lot of sense" it's hardly worth continuing the conversation.
It's stretching your credibility to the limit when you know all the answers, but cannot show anywhere in practice that your ideas have any validity.
(Maybe you have been misjudged - in that case please direct us to the site where you can show us your ideas actually work.)

 

Youtube provides a fair reflection of the real world. I expect many of those people commenting made a recent decision on who will be the new leader of the free world. Clearly their understanding of the things around them is important to all of us.

In fact if you go back through any of the threads on turbine powered vessels on this site you will see that even reasonably informed people do not readily grasp the concept. In fact most jump in and say it defeats some natural law without even thinking about it. So I have great reservations about the average joe ever recognising any great achievement with sailing DDWFTTW. It is a long way short of what anyone could realistically consider world fame. In any event it is quite insignificant compared with finding a cure for cancer as an example or even finding a critical part of the jigsaw toward a cure. Sailing DDWFTTW is not going to change mankind forever. It is an interesting curiousity for those intrigued by such things.

In fact until you referenced Mr Goodman's name earlier it had not registered with me and I have often viewed the video and others he has to demonstrate the principle. I think I have a paper on the work but have no idea who authored it. So I doubt you would find many people who could instantly recognise Jack Goodman as being world famous for anything.

So if you have a bent to be world famous I would suggest you not waste time working on a boat that sails DDWFTTW. I do not have interest in being famous or sailing DDWFTTW. There are much faster ways to become famous if that is your ambition although some might land you in jail.

Rick W

 

Whatever happened the the person who started this thread?

 

I'm not sure wheather I'm reasonably informed or just an avarage joe, but I'd love to see the math (or theory) how it really works. I allready tried kind of ask this in annother thread but none seemed to notice my humble need of wisdom in this particular matter

 

I will give you the operating conditions for downwind as I did for the upwind. I have not spent a lot of time optimising this system because I concluded it was incompatible with the upwind system. I started with the optimised upwind design and kept adjusting the air prop until I got it to work. By then I realised the incompatibility and thought why bother. Note that the only way to get the prop/turbine efficiencies I nominate is to use cambered blades. The camber is reversed compared with the upwind case.

Wind is 3m/s.
Boat is doing 4m/s (this is a long slender hull that is easily driven - based on data from one of my hulls)
Apparent wind is 1m/s from the bow.
Mechanical gear ratio is 1.1:1 and transfer efficiency is 94%.
Air propeller is absorbing 369W at 323rpm. Efficiency is 47% and pitch is 691mm (it needs to be quite large diameter as efficiency is low because apparent wind speed is very low)
Water turbine is producing 360W at 356rpm. Efficiency is 91% and pitch is 688mm.
Hull drag 62N, turbine drag 97N and prop thrust is 159N.

So it works but you have to ask why bother. It has such a narrow operating range from a wind direction perspective. The size of the prop does not translate to a good upwind turbine. There is a huge difference in apparent wind speed with the two cases.

Rick W

 

It's basically very simple, if you just start with basic physics and don't try to look it too complicatedly.

Power P is velocity V multiplied by force F: P = V * F.

Now velocity the propeller sees is the water velocity relative to the vessel and the turbine sees the wind velocity relative to the vessel. This is just the same for sail and keel. All wind driven "things" need a velocity difference between the two: air and water/land/ice.

The transmission between the turbine and the propeller transfers POWER (with some efficiency), thus the power at propeller shaft equals that on the turbine shaft. One is the "generator" and the other the "motor" depending on the situation.

As an example a boat travels 5 m/s in 4 m/s downwind. Now the propeller sees 5 m/s water speed Vp and the turbine sees 1 m/s apparent wind Vt. Without losses thus:

Pt=Pp => Ft * Vt = Fp * Vp => Ft = Fp * Vp / Vt => Ft = 5 * Fp

Thus theoratically we can have 5 times more thrust with the turbine than we have drag by the propeller. The propeller is taking power "out of water" and the turbine is pushing with that power.

Now when we add efficies, say 80% for both and 90% for the transmission, we still get Ft = 2.9 * Fp. Thus we have now Ft-Fp = 1.9 * Fp = 0.7 * Ft to cover drag of the hull and we must design a system that can perform at specified efficiencies and forces at the given condition.

Sounds easy, but when you try to design it, you notice that the turbine needs to be huge to get any meaningfull thrust at 80% efficiency in given conditions. Huge turbine -> huge vessel -> a lot of drag at 5 m/s -> not feasible. By huge I mean 20 m diameter to reach even 100 N thrust at ~80%. And then you need to have less than 70 N drag for the vessel at 5 m/s....

I believe it is far more difficult to build this on water than on land. On water the initial resistance is zero, but at the same time you can not transmit any power at low velocities without a huge propeller and turbine. On land you can use a wheel to extract power with a very good efficiency and you can go fast with little drag, since about all you have is rolling resistance. With a good bicycle the drag is only about 0.004 * mass and it is independent of speed, since we are in almost zero apparent wind. Thus for 100 kg "wind bicycle" the drag can be as low as 4 N and we need only 6 N turbine thrust in the example above.

Joakim

 

Joakim
Windmaster rightly insists that we stick with the convention of a propeller absorbing power and a turbine producing power. In the downwind case the turbine is in the water and the propeller is in the air.

You have got the basic physics correct but I disagree with the size of the air propeller. It has to be quite large but no where near the size you indicate for a single person boat.

Rick W

 

I think it has to very huge to reach 100 N thrust at 80% efficiency at 1 m/s apparent wind, BUT 80% efficiency is probably not needed. Is it really possible to get 47% efficiency at 323 rpm as you say? At what size?

The power absorbed by the air propeller is too high in your calculation, should be 339 W.

62 N drag is achievable, but you need to keep the total weight at maximum of ~100 kg in order to keep the wetted area under 3 m2 and also the residuary resistance needs to be very very low, thus very slender (= more wetted area). Would this be possible with the propeller and turbine needed?

Joakim

 

Joakim
I have posted many times on the turbine/prop boats and you are the only poster so far that has demonstrated a sound appreciation of the physics.

I have attached a JavaProp design page for a prop that will achieve close to the numbers I gave at 160N thrust in 1m/s wind. It is spinning much slower than I provided and accordingly the pitch is larger. JavaProp allows for the velocity ratio whereas my analysis does not so at the low apparent velocities my data is inaccurate. However I use slightly better foils than what is available in JavaProp so can get efficiency a percent or so better.

As I said before, once I realised how big the prop needed to be to get reasonable efficiency I did not go any further. It might be that you can do better than I have indicated if you play with prop and turbine size but I would not regard 8m as practical on the boat I was considering. With upwind you find a prop around 3m is about right for this size boat.

You are right about the power absorbed by the propeller for the stated efficiency. The figure I gave was higher than it should have been but is close to the number shown for the slightly lower efficiency prop shown in the attached.

I have not checked which hull I based the hull drag on but, for example, my V11 style hull displaces 100kg, is 7.2m long and has wetted surface of 2.1sq.m. The fibreglass hull and aluminium drive system weighs 23kg and I am currently doing an all carbon fibre version that has estimated weight of 15kg. So It is possible to make a boat with a turbine and prop for the hull drag numbers I have given. The thing is that the upwind boat would be distinctly different to the downwind boat. Now how practical is that.

I have not done analysis across all points of sailing but you have to ask how often do you really want to sail DIRECTLY down wind. It also has a narrow range of operation because above a certain windspeed the hull drag simply does not allow you to get out of the low efficiency region for the propeller so it acts as a rotary sail just retarding forward airflow rather than accelerating it backwards.

Rick W

 

Joakim
I should add that in determining the weight of the boat you can see that the power transmission requirements are quite low for the downwind boat. Gearboxes required to handle that power level weigh under 1kg.

The situation for the upwind boat is again quite different in this regard as well. You quickly get up to power levels around 10kW on a small boat. Although the air turbine is much smaller than the air propeller the gearbox to handle the power would actually be quite a lot bigger for the turbine.

Rick W

 

Thank you! I have studied quite a bit of physics, which perhaps gives a more open minded view to these things, that sound impossible at first look.

There is no real use for a vessel like this, but it is an interesting subject to think about. How heavy would a 8 m propeller and it's support be? How much wind would it tolerate? Would the boat handle well the moment?

Joakim

 

Joakim
Until you play with carbon fibre in a sandwich construction you simply cannot appreciate what the numbers mean. It has unbelievable rigidity and strength for weight. I made a 4mm thick test strip using 200gsm CF and compared with the same size strip using 320gsm fibreglass cloth. Both were made resin rich to give a nice surface finish when formed over plastic so final weigh difference is not huge. The CF ended up around 1kg/sq.m and the fibreglass a little heavier. However the CF panel is roughly three times stiffer than the fibreglass.

If I was making a 4m long blade that tapered from something like 400m at base to 200mm at tip I would use two of these panels back-to-back but only bond the inside CF initially to enable section profile over formers before doing single CF wrap around the outside. I figure I could make such a blade weighing 3kg and it would have more than enough strength. Given the loads are minute once operating, it would be suitable for demonstration purposes.

Moments are going to be nasty but then there is 75kg of movable ballast to offset the worst loading conditions. The particular hull in question is 7.2m long with 225mm beam. It would need wider set outriggers with greater volume to give some safety margin but these do not contribute to drag when going direct down wind.

I would not want to be near those blades in anything over 20kph winds. You would want to stall it before that stage and be careful about getting beam on to wind. I have been on the boat in maybe 60kph wind and at that speed you get concerned that the wind will pick up the boat and roll me and that is sitting right at water level.

I had numbers for a smaller air prop but it needs to operate at higher apparent velocity and I cannot remember if it actually worked or I still had some logic errors in the analysis.

I have posted an Excel spreadsheet on another thread:
http://www.boatdesign.net/forums/at...-out-there-they-viable-ideal_turbine_boat.xls
that has the equations you provide for the upwind case. It has a little macro that balances operating conditions.

This could be easily be converted for the downwind case but you have to use a much lower air propeller efficiency. I use interactive propeller and turbine models for particular foils but you would be able to use JavaProp for the propeller design. You can make some estimates about the turbine based on a propeller in JavaProp of similar size.

I have components to make a wind turbine but no time right now to get into making it. I expect that I will get back to it in the new year. But the turbine is intended for operation upwind or at anchor to charge batteries. It also has the capability to provide propulsion because I have a full 4-quadrant controller and BLDC motor/generator.

Rick W

 

Thing that troubles me here is the turbine/propeller concept which is here is determined by the apparent speeds of the intermediate. Messing up with energy conservation I'd like to point that in this case water gains more inertia and the air looses some so the apparent truth of a combination of turbine/propeller is in reality a propeller/turbine...
Am I thinking straight or just gear loose

 

This may be of interest:

http://uk.geocities.com/fnsnclr@btinternet.com/yachts/auto/index.htm