National Ship Design Competition. Need Help

Discussion in 'Boat Design' started by HaveANiceDay, Jan 17, 2012.

  1. Submarine Tom

    Submarine Tom Previous Member

    Then you probably wont be able to help me, but thanks for replying.

  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Tom if you offer him lines, he loses the whole point of the exercise, not to mention the race with the design you've posted.

    Some light reading and simple math will get him in the ball park, but nurse maiding him through the problem solving aspect, seems self defeating to say the least.

    Tad has answered the basic questions of hull form and stability. Assuming the OP has sufficient math skills to figure out about how much boat it will take to support his 6.6 pounds of cargo, building materials and propulsion, they can extrapolate a reasonable set of lines from what's commonly known. A displacement form is the obvious choice, likely considering the supplied propulsion unit will pretty much suck. So, the usual applies, do a weight study and work with what you have (power) for a hull shape.
  3. rwatson
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    rwatson Senior Member

    Hull design aside - one of the big issues is power versus weight.

    With electrical motors, more power = more battery weight.

    Since the course is so short, as a long time fan of electric slot cars, battery longevity and speed will be a huge part of the success formulae.

    The first question is - does the mandatory ballast have to be steel ?

    If not steel, then far better to make it all as batteries ( probably rechargeable) ,so you have an enormous power source. I would then run say 4 electric motors, at a rate that will last the 100 metres, flat out.

    If it has to be steel, and you have to have batteries as extra - you could build the steel sheet with a matching copper or zinc sheet, held in a plastic or epoxy container, separated by electrolytic paste - in effect creating a reserve of power to achieve the same thing. It would not be as efficient as lead batteries, but maybe it would give you an 'edge'.

    Check out some options on the internet about how to incorporate steel in a battery. It doesnt have to be long lived.
  4. daiquiri
    Joined: May 2004
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    daiquiri Engineering and Design

    Regarding the speed, this is imho a case which can be simulated with a reasonably good accuracy with Michlet. Contact Leo Lazauskas for help, or post a more detailed drawing (beam and draft numbers at various significant longitudinal stations) so someone can perform a run for you.

    Regarding the maneuverability, I believe it will be extremely sluggish. The underwater body will oppose a big resistance to turning moments and the rudder appears to be way to small to have any authority worth talking about. You need to define maneuverability goals first, imho, and then design the rudder accordingly.

    Seeing all that draft, I'd suggest you to not leave the helm in Capt. Schettino's hands. :p

    Last edited: Feb 1, 2012
  5. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    I don't know but I do have a 122cm LOA X 11cm draft model that is very similar ready for towing tests as soon as a tow boat is ready. One major problem with this concept as a container or bulk carrier is that it will not be stable unless well loaded and this will pose a problem at the dock. Loading and offloading will have to be coordinated to take this into account.
  6. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    I think poorly. Too much wetted surface for good speed. The stability might work. but remember that a vessel rolls about the CG, so you will be dipping the sponsons all the time which will degrade both speed and maneuverability. I think maneuerability would be horrible, not only is the rudder too small compared to the projected area as daiquiri pointed out, but it is also too low compared to the CG. Rudder force will cause a large heeling moment, which will again cause dipping of the sponsons. IMHO, if you want to go with this design, you should raise the prop shaft and rudder area.
  7. hoytedow
    Joined: Sep 2009
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    hoytedow Wood Butcher

    With the light directly overhead the photos have too much glare, making it hard to see the lines. Try oblique lighting new photos.
  8. Submarine Tom

    Submarine Tom Previous Member

    Thank you all. I agree entirely with all your comments.

    Sorry about the picture quality, I've tried many angles, this is the best I could do.

    He went with a conventional, FreeShip design. I was hoping to evolve some ideas into a winning hull but we are out of time. He cut the sections today.

    The rudder, prop, motor, battery, R/C gear is all standard for the whole nation as is the 3 kg above-water-line payload and 3 kg ballast plate.

    He's got loads of thrust from the video I've seen so hull speed will be hull speed, He'll get points in maneuverability, stability, creativity, and detailing/finish.

    Cheers, thanks again for your input.

  9. Leo Lazauskas
    Joined: Jan 2002
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    Leo Lazauskas Senior Member

    That's a very sensible strategy that worked before in a race for (larger)
    electric/solar boats in Canberra a few years ago.
    One winning entrant (an Australian ex-naval commnader) modified
    an existing long narrow dinghy by changing from a cut-off transom stern
    to a canoe stern, and using the maximum allowable weight in lead-acid batteries
    placed low down.

  10. Submarine Tom

    Submarine Tom Previous Member

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