Hydrofoil operated heeling system for a solarboat

Discussion in 'Boat Design' started by stand in bob, Oct 6, 2015.

  1. Skyak
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    Skyak Senior Member

    I am positive that you have not given it full consideration or done even rough calculations.or you would think differently.

    What's a reasonable accuracy? 10 deg? Less?

    What heel results in the panels hitting the water and what is the result? failure?

    How high are waves and what is the frequency range?

    How high must the panels be to stay out of the water?

    Now consider that you have a driven pendulum how heavy does the ballast have to be to keep the panels out of the water? Also consider the weight of the hull needed to support the weight of the panels & drive, ballast, and itself. Sum it all up and divide by the weight of the panels & drive (payload).

    Now for the cat, we need two hulls each able to carry half the weight of the panels and drive plus enough reserve buoyancy to have a natural frequency greater than the maximum wave incidence -not much more. Divide it all by the payload and you find the cat is lighter.

    The key is that the cat stiffness is a multiple of the angle but the ballast is a multiple of sine of the angle around zero.
     
  2. W9GFO
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    W9GFO Senior Member

    The Wave Glider, a commercial autonomous boat, operates with it's solar panels awash. I think the result of the panel hitting water is drag only.

    How high they must be depends upon how wide they are. As low as possible is my thought.

    A panel can be built very light. Barely more than what a deck would be - that's if you assemble the panel yourself from bare cells. Impossible to say how heavy without knowing how big the panel must be. The larger it is, the less the solar cells will impact the weight of the boat.

    The 3.3W cells that I have, reputed to be 22% efficient, weigh 7.25g ea. That's 220g for 100W. Tabbing and encapsulating will probably quadruple the weight - that's a SWAG. One kilogram per 100W I think is reasonable. I am sure a monohull could be made to be stable with that much weight one beam high. It will have electronics, motor and battery mounted down low for stability. Battery weight would be several times the panel weight, assuming it is going to be operated for more than a few hours.

    The keel would add stability while providing a method of tilting the panels, and insure self righting in the event of capsize.

    If we want to put the same amount of panels on a multihull then we would need to shorten the hull. The only weight the monohull adds compared to a multihull is the keel. You can't make two hulls two meters long weigh the same as one hull two meters long, so the multihull must either be heavier or shorter. Both serve to reduce efficiency.

    More extra weight comes from the frame work needed to separate the two hulls, the panels - which now are no longer part of a deck, the framework and mechanism to tilt the panels, extra hardware for steering (two rudders instead of one). Possibly two motors now, or some extra pod that hangs between the hulls, and a compartment between the hulls to house the mechanics. Then you also have the issue that it is no longer self righting from a capsize.

    You are right that I have not given it full consideration. But I have done rough calculations. I have been knocking around the idea of making a small solar boat, that's why I have the cells. I very early on discounted multihulls because once they go over, they stay over. I do also believe that for a given amount of panel space, a monohull will outperform a multihull.
     
  3. alan craig
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    alan craig Senior Member

    I think that Daiquiri is right and the OP is entering the Dong Solar race. We all assumed that flying meant "lifted by foils" when flying literally means flying, e.g.. surface effect and wing-in-ground-effect craft. These are probably banned. If that is the case, various videos show solar powered foiling craft banking in corners which would either negate the advantage of tilting the solar panels, or greatly increase the complication of dealing with it.

    In any case it is easy to test if it is worth doing in theory: measure the output from the panels (on shore) when flat and when tilted towards the sun. If the % increase in power is more than the % change of total weight of the craft with added tilting mechanism then it might be worth doing - if the race course is mainly east-west.

    Mr. efficiency re. your comment about what seemed obvious; thanks! maybe I'll comment a bit more. What could go wrong? it's only a forum....
     
  4. W9GFO
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    W9GFO Senior Member

    If that is true then I concede that a tilting keel is not appropriate for that type of race. I was thinking it was a long distance autonomous type race.

    Still, if the only purpose of the foil is to tilt the panel I think it best to use some other method.

    There is an autonomous wing sail catamaran that can tilt it's mast to right itself from a capsize. The keel is an extension of the mast. I wonder if the OP saw that and wanted to apply the same idea to a panel. Go to 3:30 to see it.
     
  5. Skyak
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    Skyak Senior Member

    For starters, Wave glider is not solar propelled it's wave propelled.

    You answered NONE of my questions. What is the aiming accuracy needed? More specifically, how much more efficient are panels that are aimed (output as a function of error angle)? Then we can compare the means of achieving that aim accurately.

    I am not saying solar CANNOT be sealed, I am saying it will be difficult, unreliable, heavy and inefficient.

    Did anyone but you say that this was an autonomous long distance vehicle? The OP said it was a "race competition".

    Why in the world would anyone cut the length of a multihull (in half) or limit the solar panels on it in a race competition? The fact that a multihull can carry far more panels aimed far more accurately is the entire point.

    You say you can build a solar array into a deck barely heavier than a deck without solar. Well there is a multi-billion dollar market out there dominated by products that don't come anywhere near that. Either you are a genius the world has not found or you are not smart enough to realize you are wrong. I sure hope you are the former but until you prove it we need to use the characteristics of REAL hardware for argument sake. If you can demonstrate a reliable manufacturable panel that can take the stress of a deck and frequent immersion in salt water we would all love to see it.

    Just now I see that you conceded the multihull is a better solution in a post that was not there when I started. You seem to have a very different application in mind but I am pretty sure it does not pay to tilt boat with a keel to aim solar panels. I suggest you start your own thread -tell us what you are trying to do and how. If you can make efficient structural solar decking you will certainly have the most popular thread on the site! If it turns out to be much harder than you think we can help you out.
     

  6. W9GFO
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    W9GFO Senior Member

    Yes, that is correct. You suggested that the panels might fail if hitting the water. Wave glider is an example of the panels awash - and it does fine.

    I did not answer because it is not important to me. I am assuming that aiming is worthwhile when discussing how to aim. I am not sure why you need to know precise angles.

    I gave numbers regarding the weight of cells. I said why I think it would work. Perhaps you can explain why what I described is so difficult, unreliable and heavy?

    No one said one way or the other. However the OP did say "extremely light weight" which I read as being a small unmanned boat. Apologies if I got this wrong. The OP still has not confirmed...

    I already said that the main reason would be for self righting, another that I already implied was for a limit on panel size. For a given size of panel it will be more efficient to use a long skinny monohull.

    I think you haven't really read what I wrote. I said that you could build the cells onto the deck - I even gave weight estimates. There is no commercial market for this. What I suggested would work well for a very small custom built boat. In this application the stresses are already handled by the deck. All you need to do is add the cells and seal them. You aren't going to walk on it and it doesn't need to last 20 years.

    I did not concede that a multi hull is better. I said that for a race like the Dong Solar Challenge a tilting keel is not appropriate. Yes, I did have a very different application in mind. Truly sorry that I assumed incorrectly. Congratulations to those who do guess correctly in the absence of more detailed information.

    I'll add that I do not care for your tone. Maybe you are right and I am not smart enough to realize that I am wrong, but I have tried to explain why I think the way I do - without insulting anyone.
     
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