macnab
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| posted on 13/12/06 at 11:56 AM |
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Balancing a speedboat??
Totally unrelated subject. I’m scratch building a large radio controlled speedboat / cruiser. It has a planning bottom at the back and should go like
stink with the motors I’ve fitted. I need to know (roughly) where it should balance so that I can work out where to install the cradles for the
battery packs. I suspect that it should be too the rear rather than just in the centre, i.e. over the planning section of the hull. I have angled the
props at 25 deg so it shouldn’t pitch up on power.
Would anyone have an idea??? Last thing I want is it doing a cartwheel a 40mph…
[Edited on 13/12/06 by macnab]
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silex
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| posted on 13/12/06 at 01:02 PM |
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its not easy to say without seeing as there are so many variables.
However, a good method if you are capableof running in water is to temporarily fit the batteries in using blue tac. Then you can test the batteries in
different places and get the very best setup for the configuration you have. Once you have found the sweet spot make the cradles to fit that exact
position.
Murphy's 2 laws
1. If it can go wrong it will
2. In case of emergency - refer to rule 1.
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Richard Quinn
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| posted on 13/12/06 at 01:16 PM |
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I used to race both FSR-V (multi) and FSR-O (offshore) but, as said above, it's difficult without seeing. Is it surface or submerged drive? A
side-on photo showing the hull profile, prop / rudder location etc would help.
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macnab
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| posted on 13/12/06 at 01:23 PM |
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cheers dudes,
I'll get a couple of pictures tonight and see what you think though its very similar to this boat
 
Rescued attachment boat.jpg
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macnab
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| posted on 13/12/06 at 01:24 PM |
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oh yeh and I modelled the bottom on one of these...
 
Rescued attachment torpedo boat.jpg
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Ian Pearson
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| posted on 13/12/06 at 01:25 PM |
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Is that last pic of a Nasty Class? Tasty boats!
[Edited on 13/12/06 by Ian Pearson]
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macnab
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| posted on 13/12/06 at 01:36 PM |
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hmm not sure of the class, their on the web for sale in america I think, resting on a river bank. Bit past it now as the wood planking has rotted away
some with huge holes in the side.
 
Rescued attachment lineup.jpg
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zetec7
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| posted on 13/12/06 at 07:33 PM |
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I've been building R/C model boats for years (my wife says centuries), including high-speed electrics, Chris-Craft inboards, etc., and as a
general rule for a planing hull, the boat should balance at a point approximately 1/3 of the way forward from the transom. This is a good starting
point, and all mine ended up extremely close to that in the end. If you start off that way, then ballasting will be very easy in the end. 
http://www.freewebs.com/zetec7/
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