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

    Now I'm trying to build the boat attached, it's a sailboat very skinny and long, shouldn't tilt too much and be pretty stable thanks to the deep keel.
    Negative points in using sailboat hulls are the very limited space inside to host electronics and batteries, the absence of stabilisers and the lack of pre-arranged motor fin.

    Do you have an example of the control surface you're talking about? Can it be fixed or does it need to be moved using a servo?
    For the batteries onboard I prefer to have a greater capacity and try to stay powered as much as possible, because whenever there is a power loss the boat will become a dangerous drifting buoy, no collision avoidance algorithm in place or navigation system and no GPS position sent out to the ground control station.
     

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  2. BlueBell
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    BlueBell Ahhhhh...

    Well you never listed space as a requirement.
    Box cross-section hull then, like a freighter (a deep sea vessel) but long and skinny.
    20 : 1 length to beam ratio.
    Over-battering is a huge waste of weight,
    and weight is the enemy of speed.

    Yes, you need a self-stabilizing servo to operate the vertical strut canard.
    But only if you find roll issues during sea-trials.
    Google "canard" and you may better understand...
     
  3. BlueBell
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    BlueBell Ahhhhh...

    And why two motors?
    One is more efficient.
    One prop.
    One rudder.
     
  4. bhnautika
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    bhnautika Senior Member

    Anelito you don’t need a long deep fin keel and bulb to make a boat self righting, its just a lot of drag and something for things to hook on to. Maybe something like a modified box keel to put the batteries in for ballast.
     
  5. BlueBell
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    BlueBell Ahhhhh...

    Bhnautika,

    (S)he is also looking for:
    "Useful extra requirements would be a very good stability and ability to recover from capsizing."
    A long, deep, high aspect ratio, bulb weighted keel with an automatic canard (if necessary) would accommodate that and eliminate capsizing.
    If designed correctly, nothing would catch or get hung-up.
    Submerging the bulk of the gear in a pod at least 3 diameters below the surface would reduce drag, leaving only the panel and antennas (flush mounted) on the surface.

    But there remains fundamental problems here.
    How is a 2-knot vessel going to overcome strong currents?
    As described, this project is doomed.
     
  6. portacruise
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    portacruise Senior Member

    Blue Bell,
    The SeaCharger above traveled 2413 miles in 41.4 days from California to Hawaii at an average speed of 2.43 miles per hour. Then on to New Zealand 6480 miles in 155 days where the rudder died 300 miles short. But I did not find its designed cruising speed. I don't know how it managed to do that, unless it never encountered opposing ocean currents (or rode currents?) and also somehow steered around floating weed and debris fields that would interfere with the propeller. Unless I missed something?

    PC
     
  7. bhnautika
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    bhnautika Senior Member

    BlueBell have a look at any self righting life boat, all have ”good stability and ability to recover from capsizing” I haven’t seen too many with long, deep, high aspect ratio, bulb weighted keels. This is a small boat, half the size of the Seacharger , being too light may be more of a problem so putting the bulk of the gear in a pod may not be worth the effort after all its about getting the vcg to where it works for you.
     
  8. Doug Lord
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    Doug Lord Flight Ready

  9. SamSam
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    SamSam Senior Member

    There looks to be two parts to this project, the first is making an autonomous boat and the second is performing a task with it.

    Sailboats are designed to be operated more or less on their sides and are shaped accordingly and are usually not generous of space. A boat for this project should be designed to operate level.

    If all the thing has to do is get from here to there, it only has to have room for it's propulsion system. If the thing needs to carry other equipment, it needs to be designed for that.

    If it was designed more or less as a cargo ship, it would have more space and be more adaptable to install equipment needed for other possible research projects.

    There are thousands of autonomous remote information gathering floaters out there already, so this boat would need to offer some advantage over others for it to not be redundant. If all this boat is for is to advance the art of autonomous boats, then the shape of it isn't so important. In fact, you might learn more from having a bad hull shape in so far as developing systems for propulsion and navigation. If you can maneuver a bad shape from here to there successfully, how much easier using a good hull shape?

    How much money do you expect this to cost? How often are these things 'lost at sea' and never recovered?
     
  10. SamSam
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    SamSam Senior Member

  11. SamSam
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    SamSam Senior Member

    Here's the original being hauled onto a passing ship after it went dead in the water after 5 months and 6500 nautical miles. It's got barnacles and some tan stringy stuff hanging from it. It looks like it has no anti-foul bottom paint, that would have helped.

    [​IMG]

    Tracking http://www.seacharger.com/tracking.html


    .
     
    BlueBell likes this.
  12. BlueBell
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    BlueBell Ahhhhh...

    Imagine how far it could have gone without all those catch points!
    Poor, amateurish design.
     
  13. BlueBell
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    BlueBell Ahhhhh...

  14. Anelito
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    Anelito Junior Member

    The SeaCharger suffered from severe rudder and propeller damage, a similar fate was also the reason of failure for a lot of MicroTransat participants.

    Catch point removal is something I am really considering, it would need to recalculate the centre of gravity of the boat as well as bulb relocation. Maybe using lead in the keel without any bulb?
     

  15. portacruise
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    portacruise Senior Member

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