Feedback on a mini unmanned boat project

Discussion in 'Boat Design' started by bigkahuna, Dec 21, 2017.

  1. bigkahuna
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    bigkahuna Junior Member

    I'm toying with the idea of building a USV (Unmanned Surface Vehicle) that will be used as a sonar survey tool in shallow, protected water (bays, lakes, etc.). I want to be able to launch and operate in water 1 foot deep. This boat will be radio controlled, powered by two electric thrusters (each capable of 11+ lbs force) and will carry roughly 20-40 lbs payload. I picked a catamaran hull for greater lateral stability. I'm trying to stick to flat bottomed and simple curves so I can construct it quickly and cheaply from thin plywood (1/8" hull and 1/4" frames?) and a light fiberglass skin. I hope to keep the construction relatively light so the entire vessel can be carried / launched by a single person. I'm not certain on the LOA and beam yet, but I'm hoping it will be around 4 foot LOA. Below is a simple graphic to give you an idea what I'm thinking. I hope to design this in DelftShip (free) and use it to print out full sized frames and panels.

    A couple potential issues I see as I look at the design is that it might be a bit too fine in the bows and I wonder if it might be better to make the hull symmetrical fore and aft (ie. make it a double-ender)?

    What do you folks think?
     
    Last edited: Dec 22, 2017
  2. jorgepease
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    jorgepease Senior Member

    Why not just keep it simple and make it a flat bottom. That will give you the biggest payload and least draft and it will be plenty stable.
     
  3. bigkahuna
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    bigkahuna Junior Member

    Good point, I may be over designing this a tad bit. ;)
     
  4. jorgepease
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    jorgepease Senior Member

    I like the idea, I've wished for something similar so I could scout out depth over a long flat before committing to cross it, especially since we are mostly hard bottom!
     
  5. kerosene
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    kerosene Senior Member

    Insulation foam with pva glue and fiberglass epoxief over
     
  6. messabout
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    messabout Senior Member

    A flat bottom skiff like boat, 48 inches LOA i5 inch chine beam, 4 inch draft, will displace roughly 50 pounds. Say ten pounds of boat and 40 pounds of payload more or less..............There are plenty of well proven designs for that sort of boat.

    You need to describe what you want the boat to do with a bit more detail, such as speed, expected surface condition of the subject body of water , range of operation, duration of run, etc...

    Post a preliminary drawing of whatever you have done so far.
     
  7. portacruise
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    portacruise Senior Member

    I think a single flat hull will be better if you will be operating at planing speeds. Probably a pontoon is better if both stability and efficiency to get greater range, are important.

    PC
     
  8. upchurchmr
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    upchurchmr Senior Member

    What does your sonar gear weight?
    Do you need the boat to be stable so you can get a reference position for your sonar?
    What kind of a sensor head will it have?
    Can it look thru the hull or can it be dropped in the water?
     
  9. bigkahuna
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    bigkahuna Junior Member

    Less than 10 lbs, batteries about 15 lbs, other electronics less than 10 lbs.
    As stable as we can get for a vessel roughly 4 feet LOA. I'm considering making the design "semi-submerged" but that would result in greater depth requirements. Definitely non-planing. I'm leaning towards a catamaran style like the attached photo.
    Small, hull mounted sonar transducer. GPS and UHF antennas.
    No, the transducer will have to be in the water. Either mounted to the hull or a strut. Forward of the thrusters and always in the water.

    catarob-devant-contener-au-sol.jpg
     
  10. fredrosse
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    fredrosse USACE Steam

    Looks like the picture you post is just right. Very easy to make the hulls with 1/8ply. Adjust the beam of the two hulls for the displacement/draft criteria you want.

    I made a model of my steamer the same way, and that model is 4ft long x 1ft beam, with 20 plunds bouyancy at a couple inches draft. If you made two similar hulls you would meet your design goal. I can give you the hull in Freeship if you wish.

    Several propulsion options are available for weedless systems
     
  11. bigkahuna
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    bigkahuna Junior Member

    @fredrosse - I'm thinking of giving it a flat bottom, some flare to the topsides, and doubled ended (almost exactly as shown in the photo). I have DelftShip (free) but haven't used it in a long while. Do you know if I can print out full sized panels using it? What did you frame your model with? Any photos?

    For propulsion I have a couple of these.
     
  12. portacruise
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    portacruise Senior Member

    BigK, those motors are probably not very efficient, if that is an important requirement for your battery range. It would appear that the water gap at the armature instead of an air gap introduces additional drag and the small prop not particularly efficient. Also, I wonder why the motors are only tested to 300 hours, seems like an assurance to thousands of hours might be in order for USV.

    In shallow water, having some kind of weedless propulsion configuration might be a consideration. The described prop and cage system seems vulnerable to weed fowling.

    Hope this helps,

    PC
     
  13. Earl Boebert
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    Earl Boebert Senior Member

    Actually, if I were faced with your requirements, I'd seriously consider William Atkin's "Rescue Minor" design, especially if you anticipate weeds or grass. Lots of info on the net. Successful models have been made.

    Cheers,

    Earl
     
  14. kerosene
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    kerosene Senior Member

    Rescue minor is a pointless choice here.
    Delftship or free later version of freeship will allow unfolding panels to templates. Just pay attention to the developability when designiing as the software will also unfold shapes that don’t like to exist in 2d.

    I think you could just get 1” insulation foam and go to town without too accurate plans.
     

  15. fredrosse
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    fredrosse USACE Steam

    "What did you frame your model with? Any photos?"

    The 4 ft long model has been up in the rafters for years, but I took a couple of quick pictures. Since this was to mimic a 20 ft boat, and the frames on the full size boat were to be ordinary 2x4 lumber, the model frames are made approximately to scale, from pine, 7/8 inch x 3/8 inch, only. The light plywood hull was glued together, then covered with ordinary automotive store fiberglass cloth, all gluing and fiberglass saturation with the auto store "fiberglass resin". The large hull was built in a similar method, but with epoxy rather than the automotive resin. Simple flat bottom hull, mimics a New England Sharpie type hull.
     

    Attached Files:

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