need help to find boat size and hull

Discussion in 'Boat Design' started by sidthecoolguy, Sep 14, 2007.

  1. sidthecoolguy
    Joined: Sep 2007
    Posts: 13
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    Location: Arlington, Tx

    sidthecoolguy Junior Member

    hi, i am a student working on a project for ASV Autonomous surface (water surface) vehicles.

    Dont know much about boat designing.

    We are trying to build an unmanned boat (small between 3ft-12ft long)
    I need help to figure out the the size of the hull (dimensions) of boat i need to carry a payload of 50lbs.

    We are trying the buy the bare hull based on rc boats to make things easier.
    So need help in deciding which size to buy.

    Also we are looking for maximum maneuverablity and speed is not an issue(max speed is 10mph). Would like to know which type of hull would be the best for this purpose (monohull, catamaran, triman etc.) some hull used for rc boats that i can get from the market for my purpose.

  2. Guest625101138

    Guest625101138 Previous Member

    The first place to start is to make an estimate of total weight.

    A 50lb payload is not insignificant. Well beyond what most radio controlled boats will handle.

    Payload 50
    Boat Hull 40
    Engine and drive 20
    Energy source 50
    Contols 10

    Hence total displacement 170lb.

    The best off-the-shelf type hull might be a sit-on kayak like the attached.

    10mph for a hull like this is an issue. It will require more the 1HP. If you use a petrol engine then the weight of the energy source will come down but it will be noisier than electric. A 50lb battery might give some usable range.

    If the payload is going to sit high then you might want greater stability so a catamaran might be better. If you keep heavy parts low it will help.

    So if you do your own numbers on the total displacement there may be other options open up.

    Rick W.

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  3. sidthecoolguy
    Joined: Sep 2007
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    Location: Arlington, Tx

    sidthecoolguy Junior Member

    hey thanx for your help Rick

    The 50lb payload includes everything, the engine, the props, the battery .....

    We plan to use controllers on the boat. And the ones we use work with electric engines only. So engine type is not an option.

    So who would you consider that. I think the V hull would be the best option. But as i said i dont really know about boats. So what would you suggest.

  4. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    Fresh water weighs 62# a cubic foot (saltwater=64#) which means it takes 62# of weight to displace 1 cubic foot of water. If you had a straight sided box/boat 3' long, 1' wide and 1' deep, that would be 3 cubic feet. 3 x 62 would be 186. 186# of weight in the boat (including the weight of the boat itself) would put it level with the water, ready to sink. Half that weight, 93#, would sink the boat 6", leaving 6" of freeboard above the water.

  5. Guest625101138

    Guest625101138 Previous Member

    Hull weight say 20lb contents say 50lb. Total is 70lb.

    If you are firm on the 10mph (14.7ft/sec) and maximum length of 12ft then it will be a planing hull. A first approximation for the drag is 1/8th of the total weight. So drag force is 9lbf. Power required is 0.5HP allowing for 50% overall efficiency.

    A hull with wide, flat aft sections will take less power than a "V" hull to plane.

    There are some large model boats but they are usually very expensive in the size range. 70lb is heavy for an off-the-shelf model boat. Still think you are best off looking at sit-on kayaks or surf-ski if cost is an issue. These are solid and robust so provide a good starting point.

    Rick W.
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