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Author Topic: Lateral stability when planing - any suggestions?  (Read 1344 times)

Allnightin

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Lateral stability when planing - any suggestions?
« on: August 07, 2013, 04:33:25 PM »

I have used the Dean's Marine micro radio gear to get an Airfix 1/72nd RAF rescue launch working and the results are quite impressive with it running well on the plane at quite a low throttle.  However on right hand turns the boat banks to the right very steeply (prop turns anti clockwise when viewed from astern)  and she seems to be very close to going over.  I tried putting a small amount of ballast on the left hand side (a 5p coin) of the hull bottom but this doesn't seem to improve things.  What is the best way to counter the roll (presumably caused by the motor torque) and is weight higher up part of this?
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Perkasaman2

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Re: Lateral stability when planing - any suggestions?
« Reply #1 on: August 07, 2013, 05:43:32 PM »

Too much top weight or heavyish components not close enough to the bottom of the hull is the likely cause. It's tricky to achieve stability and engender roll resistance in such a small hull but the factors above are a guide to understanding your problem.
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CGAux26

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Re: Lateral stability when planing - any suggestions?
« Reply #2 on: August 07, 2013, 09:43:40 PM »

Sounds like torque reaction.  Prop turns left, torque heels boat to right.  Is it a deep vee hull?  That will make it worse.
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longshanks

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Re: Lateral stability when planing - any suggestions?
« Reply #3 on: August 07, 2013, 10:04:13 PM »

Might be worth trying a small wedge on the bottom of the hull at the back on the side that drops!
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malcolmfrary

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Re: Lateral stability when planing - any suggestions?
« Reply #4 on: August 07, 2013, 11:15:10 PM »

Rather than a wedge, which would put drag on that side, perhaps a small horizontal tab under the transom on that side to break the transom drag on the right hand side.  Maybe a spray rail along the chine on that side, again, to break the water flow that grips that side when its turning that way and the prop is trying to shove it further.  Maybe mounting the rudder a little to the left. at right angles to the hull bottom would introduce a tendency for the stern to lift a bit in right hand turns, countering the tendency of the prop to shove it deeper.  Of course, it might just be over powered and need to slow for corners.
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