Choosing the best marine hull for an autonomous boat

Discussion in 'Boat Design' started by Anelito, Aug 6, 2018.

  1. Anelito
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    Anelito Junior Member

    I've come to the conclusion that having a small wing-sail is necessary. I will still cover the hull with mono crystalline solar cells but I will also try with the sail, a mixed approach, so that when there is not enough wind the engine can be turned on and the sail set in neutral position (a kind of reefing).
    What do you think?
     
  2. JamesG123
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    JamesG123 Senior Member

  3. Anelito
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    Anelito Junior Member

    Haha good reference.
    Now I'm following calculations on this paper in order to dimension the main wing properly. Are RC sailboat hulls able to sustain a rigid sail with the same CG of the paired soft sail?
     
  4. SamSam
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    SamSam Senior Member

    Will this be a direct drive boat?
     
  5. Anelito
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    Anelito Junior Member

    No I will use a belt for the first tests then move to a proper gearbox.
     
  6. portacruise
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    portacruise Senior Member

    James, some very good ideas from that Portuguese man-of-war! A flexible and transparent boat sail will let some degree of sunlight through to the solar cells. A flexible sail that spills excess wind and light, cushioned G-Shock construction that bounces back, plus a long but retractable keel which might help with controlling wind spill and navigating the shallows.
     
  7. portacruise
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    portacruise Senior Member

    The motor in the link I posted above shows a way of circumventing need for gearing by using a much larger motor (2.3KW run @ 30 W max for 5 kph) if you want to use direct drive, but the total weight may increase. Weeds and debris are the extreme enemy of large diameter efficient props. One of the previously posted pictures above shows very small sheltered position props were used in the SS, yet they were still efficient and weed resistant due to size and positioning.
     
    Last edited: Aug 28, 2018
  8. Anelito
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    Anelito Junior Member

    Yeah I plan to make the wingsail with Oracover transparent film, similar to (cheap) balsa RC plane wings. For the flexibility of the sail I don't find it a useful feature to have since the reefing is quite easy in case of strong wind.

    Retractable keel? Things would get way too complex.
     
  9. portacruise
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    portacruise Senior Member

    Will a ridgid sail survive possible tumbling and wave or flying water impacts in a storm and is there sealed bearings to survive possible salt incrustation on the freewheeling ridgid sail and control mechanism... on the other hand this may have already been successfully tested to a great degree.

    Agree that the retractable keel idea is not practical.

    PC
     
  10. Anelito
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    Anelito Junior Member

    Advancements on small sailboats are mostly bond to wingsails.
    A very interesting hull shape, which interestingly resembles a shark, is the A-Tirma designed by the University of Gran Canaria.
    [​IMG]

    Having two sails, the boat doesn’t need a rudder and the whole design is engineered to avoid catching debris.

    I think I could replace the two sails with just one, a bit bigger, and place a rudder. Not sure about the two thick stabiliser pins, in the design document they should have been mobile but then were made stiff.
     
  11. CDBarry
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    CDBarry Senior Member

    Matching the propeller to the system is probably the most important issue; note that low speed props turn slowly and are large, so a reduction gear might be needed. A Kort nozzle might be a good idea.

    The remark about insulation foam is appropriate AB polyurethane foams compatible to most resins. Polystyrene is not; resins dissolve it.

    Look at the design Saildrone is using for some insight, but basically you need to start by guessing how much weight your boat will weigh, then design a hull that carries that much weight, then figure out how much the whole thing actually weighs, and perhaps resize the hull and start again. This is a good application for a simple spreadsheet using "primate coefficient" and similar concepts you will find here.

    You will need a ballast keel to make it self-righting.

    At the relatively low speed, hull speed is not very important; with a good prop, a cylinder with points on each end might be good enough.

    In terms of a more optimum hull, consider that you are basically looking for a small boat for rough conditions with very low power; a kayak.
     
  12. Anelito
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    Anelito Junior Member

    Won't s Kort nozzle get easily tangled with seaweed?

    If I make a the keel empty and let the water flood it to save on weight?
     
  13. BlueBell
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    BlueBell Ahhhhh...

    Polystyrene is fine with epoxy.
     
  14. BlueBell
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    BlueBell Ahhhhh...

    If you shadow a solar panel with even a shroud line, you will loose significant power.
     

  15. Anelito
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    Anelito Junior Member

    I know, but I am now moving towards a mixed wingsail+motor solution. The A-Tirma looks great but unfortunately their design is not open source...
     
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