Choosing the best marine hull for an autonomous boat

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

  1. JamesG123
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    JamesG123 Senior Member

  2. IronPrice
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    IronPrice Senior Member

    If the solar panels are under clear plastic is a nice idea, but the plastic may be obscured by salt deposits and if it stays wet enough, will probably grow algae as well.

    Then again, this problem is likely to apply to the panels themselves.
     
  3. Dolfiman
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    Dolfiman Senior Member

  4. Anelito
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    Anelito Junior Member

    I'm actually using part of their code, it is very detailed. Just to mention a small example, every 5s the controller checks wind direction and speed and calculates the best tacking angle using a look-up table with angle of attacks paired to lift coefficients.

    Anyway, A-Tirma team kindly shared their G3 design, which is totally different from the pictures online. I can't share the whole frame, but simply taking a look at the midpoint section you can see how the all-rounded shape was replaced by a more faceted version.
    Won't those sharp edges create a lot of drag? Apart from that, I noticed they use a pair of oblique skeg rudders with the propeller in the middle, quite uncommon.
    [​IMG]

    Going to the wingsail, do you have a reference on how to pair the LOA and the sail surface?
     
  5. HJS
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    HJS Member

    Won't those sharp edges create a lot of drag?

    If the chines are placed in the right place, they contribute to stability and performance. I have applied it to all my boats for the last fifty years. I have never heard anything negative about it. But you have to know how to do it.

    JS
     
  6. portacruise
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    portacruise Senior Member

    Is drag important with such a small boat that is barely moving above drifting speed? Stability, weedless performance, (and how long does barnacle paint last?) and anything that prolongs functions for the very long term should be higher priority, IMHO. What happens if the tiny craft is repeatedly caught at the tip of 15' waves or buried at the bottom by such waves, or slams into hard trash/debris during a storm?

    PC
     
  7. Anelito
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    Anelito Junior Member

    I see your point, interestingly sail buoy managed to survive for almost three months while being remotely controlled.
    The boat could try to avoid storms and bad weather as much as possible with accurate route planning and fill up the hull with foam to prevent leaks.

    Now I am trying to design the wingsail, taking inspiration from (the few) existing designs and this paper.
    Starting from the NACA profile, I’m now considering the 0012 and 63-012 from the ASPire project.
    Using the ASPire measures and scaling down for a 1.5m loa, I got that the wingsail height should be 1m with 26cm chord (thickness ratio 16% ~4cm).

    The ASPire uses a linear actuator mounted vertically in the mast to move the tail. Now commercial actuators are too big to fit inside the small mast I will be using so I opted for the solution depicted in the paper. A few images of how the sail would work.
    [​IMG] [​IMG]
     
  8. Anelito
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    Anelito Junior Member

    Back here, the main hull is finished, now I'm thinking about the keel. Considering the 1.5m final size, the keel will be 38x25cm, simple, no NACA shape. How about the size?
     
  9. BlueBell
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    BlueBell Ahhhhh...

    That depends what the hull looks like.
    But, generally, as deep as possible.
     
  10. Anelito
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    Anelito Junior Member

    What about thickness?
     
  11. portacruise
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    portacruise Senior Member

    My opinion on the keel is to consider weed/debris shedding shape 1st, then length into the water to maintain upright position on such a small boat (for stability), and 3rd best foil shape for greatest efficiency. Some of these things work against each other, so a compromise shape will be required.

    PC
     
  12. JamesG123
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    JamesG123 Senior Member

    As thin and low drag as you can get away with.
     
  13. Anelito
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    Anelito Junior Member

    At the local Maker Faire I’ve seen a very interesting concept for a high performance keel with integrated propeller in the bulb.
    The keel is telescopic and retractable, made of 5 sections that slide one in the other in order to adapt to shallow waters.
    The keel itself and the bulb rotate independently for trimming and direction purposes (similarly to an azimuth pod).
    That’s the only image I found
    [​IMG]
     
  14. portacruise
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    portacruise Senior Member

    If you need shallow water capability, maybe some kind of self-righting cat or Tri Hull might be simpler than a telescopic Kiel. A search on this list will yield information about self- r i g h t i n g h u l l s, and there are some RC boats that are claimed to be self-righting also. The Keel in the picture looks like a weed catcher, but even the most streamline Kiel loses its efficiency once weeds become attached to it.
     

  15. IronPrice
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    IronPrice Senior Member

    Looking at that telescoping keel ... it would make sense to build in a function to fully retract and extend the keel at least once per day, to wipe off any marine life while it is still small.

    I something like a barnacle gets established, it would cause jams in the telescoping function.
     
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