Can solar energy power a catamaran?

Discussion in 'Multihulls' started by EscapeArtist, Sep 4, 2016.

  1. W9GFO
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    W9GFO Senior Member

    Here's a guy making a 30 mile coastal trip in a pure solar powered catamaran (no battery).

     
  2. groper
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    groper Senior Member

    Nice to see him having a go... but if you think you can reliably sail something like that in all weather conditions, in open waters, then you don't have enough experience to know better. You would be setting yourself up for a date with coastguard rescue if you were caught in a blow in a boat like that...
     
  3. EscapeArtist
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    EscapeArtist Junior Member

    Nice video - thanks Moondog!

    I just downloaded Free!Ship and will try to estimate power requirements from that, but a real resistance curve would be better.
     
  4. CT249
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    CT249 Senior Member

    If its an ocean, why is the water so flat and why is there land on each side?
     
  5. groper
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    groper Senior Member

    Heres the resistance vs speed graph for my 11m cat EA. This could be improved as this boat was designed for 20kt speeds and has a full transom which increases resistance at low speeds. I would suggest it could be improved upon slightly with a different design hull.
    [​IMG]

    As its difficult to see, the data point @ 8kts (4.1m/s) is 1.57kN.
    1.57kN x 4.1m/s = 6.437kW
    assume with large diameter high efficiency props, you might get 70% prop efficiency, thus you would need 9.19kW from the motors. Allowing electrical efficiency of the motors @ 93% = 9.88kW electrical power input.

    So i was pretty close in my estimates based on the fact ive owned multiple boats including an 11m and 12m catamarans... The electrical and propulsion systems for such a boat, as an electrician i could build it for approx $40k give or take without making detailed quotes. This is comparable to installing a couple of diesel engines... This demonstrates that the idea is feasable for short distance hops. For a coastal and or bluewater long distance cruising tho, i would much rather have sails - no doubt in my mind whatsoever about that...
     
  6. W9GFO
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    W9GFO Senior Member

    I don't believe that was the question - all conditions, open waters.

    What you can learn from that video is that it is possible to power a boat under solar power alone. Also consider that he used no MPPT charge controller to maximize solar panel efficiency. No storage battery, his motor was an inefficient PM motor and his prop was hand made.

    Some other guy crossed the english channel in a solar-only catamaran, and there are dozens of other solar powered boats out there now. There really is no question as to whether or not you can get enough power from the sun to move a boat. The question is, can you accept the compromises that you will have to make?
     
  7. groper
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    groper Senior Member

    Indeed, its all about the compromises and what the intended use is... however the OP was asking about this concept in the context of coastal cruising.

    This illustrates the solar VS wind for "bluewater usage" point quite nicely i think;

    Both boats compared here are the highest technology examples mankind has built to date - both have a similar length, and similar budget, both were designed and built to break round the world records.

    Transatlantic crossing record, 5330km.

    Solar power
    Time Boat year Mean speed
    22d 12h 32min Planet Solar 2013 5.4kts

    Wind power
    Time Boat year Mean Speed.
    3d 15h 25min Banque Populaire V 2009 32.94 kts

    Enough said?
     
  8. W9GFO
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    W9GFO Senior Member

    Enough said??? As in, these two examples "prove" that a solar powered coastal cruiser can't work? Then no, there is not "enough said".

    Thousands of cruisers are content (indeed, quite pleased) to make 100 mile days. That's part of the compromise. Personally, I don't care about speed. The destination is to be on the water, that's why I like boats, not to end the trip as quickly as possible.
     
  9. groper
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    groper Senior Member

    no its not just about the speed - it illustrates the point of available energy...

    people have paddled kayaks across the atlantic too - almost anything is possible, but is it really practical?
     
  10. mydauphin
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    mydauphin Senior Member

    A sailboat is better, and can handle the weather better, and it is cheaper. Get 26 foot sailboat, monohull with a good deep heavy keel. Put a couple small solar panels, a wind generator, a torpedo electric outboard, three batteries, a small 5hp emergency gas outboard. Rig everything heavy duty, get a emergency survival suit. Fill the rest of the boat with 5 gallon buckets of food and water, tie everything with rope. And now you can cross an ocean with solar power.
     
  11. groper
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    groper Senior Member

    And this also proves that some still dont understand the problem. Do you have any idea how difficult it would be to make 100mile days, in open water, with a solar boat???!! If you were faced with 20kt headwinds and head seas, which is a very frequent real world scenario, even an extremely well funded solar boat costing an order of magnitude more than a typical sailboat, would be lucky to make 20 miles assuming the sun was out, all 8 hours of it... meanwhile the wind continues to blow all night long and for the next week straight...

    And thats the whole point, you could spend a bomb trying to make a solar something that can compete with wind power and youll simply never get there because of the energy deficit. Lots of distance = lots of energy.

    Oh but what about the days with a tail wind? well now your solar boat will make a 100mile day, congratulations, but the sailboat has already dissappeared over the horizon and spent the last 3 days enjoying the beautiful islands tucked away in safe anchorages. Meanwhile the next storm rolls in and catches the solar boat before it can reach safety. The sun is gone and your dead in the water waiting for sunrise... I could go on but suffice to say the challenges are endless for long distance applications and noone in their right mind would want the limitations you have to accept, especially when the boat will be so expensive... your chasing a white elephant.

    Short distances, calm waters, and other applications where you dont need much energy are a whole different ballgame tho and i argued earlier that for these purposes, a solar boat could not only work well, but also be cheaper in the long run.
     
  12. EscapeArtist
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    EscapeArtist Junior Member

    groper - Thanks for posting the resistance/speed graph. That's very nearly linear, which means that power is only a quadratic function of speed.
     
  13. W9GFO
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    W9GFO Senior Member

    ... and you don't seem to understand that someone that is willing to make the compromises necessary for a solar boat will not put themselves in that situation - assuming they are sensible. The original question was if the Sun could power a coastal catamaran, not a blue water passage maker. The answer is yes.
     
  14. groper
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    groper Senior Member

    You could paddle a kayak across the atlantic...
    You could power a coastal catamaran from the sun...
    You could even power a bluwater passagemaker from the sun - oh wait its already been done...

    Its never been a question of whether it could be done, planet solar proved it years ago - did you miss that? The discussion, not a question, has always been about practicality, suitability and feasibility. But you seem to have missed that too which makes me wonder - have you any experience in real world coastal cruising?
     

  15. W9GFO
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    W9GFO Senior Member

    I get the feeling that you have decided that there is only a very narrow range of circumstance where you would support a solar powered boat, anything outside of that is pointless. And that is fine. I think that a small solar powered coastal cruiser could work quite well, providing you are willing to accept the compromises necessary to make it work. Further, I do not think it would be prohibitively expensive, although it would not be cheap either.

    I do think that if you want a solar cruiser that performs in all circumstances the same as a sail or diesel powered cruiser, then that is not possible.

    Yes, I have experience.
     
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