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Model boat hull shape

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themeaningoflife View Drop Down
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    Posted: 14 Jan 12 at 5:55pm
Hi all,

At the last minute I have found out that I am entered in a school competition to deign and build as fast a solar powered motorboat as possible! The boat doesn't need to be able to turn or carry any load, simply go as fast as possible over a set distance in a tank that means there will be no waves. In essence the boat needs to be as quick as possible in a straight line on falt water. Does anybody have any ideas for hull shape or similar aspects of the design? I personally was thinking about something similar to http://www.conceptistech.com/products/linkapix/puzzle_samples.htm#lap_mega ?
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Post Options Post Options   Quote Max McCarthy Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 12 at 6:05pm
The link hasn't worked, but marine modeling international did a similar thing. The idea, I think is they took solar panels from solar powered garden lights, made th boats out of as light material as possible, and as small as possible for the available solar panel. But these were full radio control, and if you only need a small motor, then there isn't any point in full radio control. I would have thought, if you use a 250 size motor, and solar panels to suit, then it should fly, if you use a small enough hull.
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 12 at 6:21pm
As long and as thin as possible would be a good start... What are the design parameters? A catamaran would provide plenty of area for the panels, plenty of stability and low drag. If you don't need the area maybe a foil stabilised trimaran like Ilan voyager.

Lets think.
Semicircular hull mid sections at the designed displacement.
Max beam at I should think 65% of length. Dead straight waterlines from bow to mid section, vertical bow,little rocker to mid section.
Rocker from mid section to stern section flattening from semicircular
transom not quite immersed.
I reckon that's a sort of "ought to be thereabouts" shape.
Straight entry to vertical bow
But you need to design it around the Solar panels and the power unit(s).
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Post Options Post Options   Quote themeaningoflife Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 12 at 10:46pm
That's brilliant thanks :) also would a very flat, tray-like shape well for planing? I was thinking of possibly that with a long, deep, thin skeg to keep it tracking?
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Post Options Post Options   Quote themeaningoflife Quote  Post ReplyReply Direct Link To This Post Posted: 14 Jan 12 at 10:49pm
Just realised that the boat I intended to link to in the OP is Earthrace, the recently sunk Sea Shepherd's boat.
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Post Options Post Options   Quote Andymac Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jan 12 at 8:26am
You need GRF's V twin!!!
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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jan 12 at 10:49am
I don't think you'll get the boat planing. As Jim says, long, thin catamaran hulls. I'd go for narrow with plenty of height to keep the platform for carrying the solar panels well clear of the water. Try balsa wood as a construction material.
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Post Options Post Options   Quote Max McCarthy Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jan 12 at 10:54am
Or maybe that blue foam type stuff I cant remember the name of, which is very fine, but pretty strong and light, covered with some sort of epoxy. You could model it off an ac45, long thin hulls, and a skeg and motor (250 size?) if you got it about 25 cm long, you could have it light, relatively wide and a lot of power for the weight. So I think Jim is right.
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Post Options Post Options   Quote laser193713 Quote  Post ReplyReply Direct Link To This Post Posted: 01 Feb 12 at 12:36am
A little thing to consider is that the propeller should be kept as close to a hull surface as possible so that it is working in the boundary layer of the hull.  This increases its effective angle of attack compared to a propeller working in an "open water" condition.  If you are only allowed a single motor and single props then perhaps a cat would not be the most efficient.  A tri might be more suitable.  If you think you will get it planing then a dory type hull might be the most stable, i would suggest fitting some sort of trim tab that is finely adjustable to keep the thing in a straight line.  

We did a very similar project as a module of our degree in first year.  PM me if you want any details of the boats that entered and how they did.  I will try and dig them out!
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