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Author Topic: help with stability  (Read 1101 times)

pintheair

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help with stability
« on: September 14, 2013, 12:25:29 PM »

hi need help , have scratch built skat 9906 , but is a bit top heavy so leans out when turning,
ply constructio , chine hull at rear, 12v 8a lead-acid batt as ballast,
just fitted two rudders on sides at 45 degrees linked to main rudder as stabilizers
what else can i do?

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unbuiltnautilus

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Re: help with stability
« Reply #1 on: September 14, 2013, 01:17:13 PM »

Well, you could add a  bit more ballast low down to take her down a little more, repaint the waterline to disguise the change in draught, I think the look of the model wont be compromised by this mod.
If not, I had a top heavy Torpedo Boat Destroyer back in the day, rolled over three times, fourth time it sank! I fitted a small ball of lead on a removable square brass tube, which was slid into a larger square tube bonded into the hull midships, took it out for display and fitted it for sailing. I could run that model in a gale after fitting the keel.
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Colin Bishop

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Re: help with stability
« Reply #2 on: September 14, 2013, 01:24:37 PM »

The problem could be caused by the lead acid battery, especially if you have mounted it in an upright position. Cylindrical NiMh cells in the bottom of the hull would lower the centre of gravity substantially and the 5ah versions would deliver a similar running time to your lead acid battery.
 
Colin
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tony52

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Re: help with stability
« Reply #3 on: September 14, 2013, 02:50:49 PM »

In the 2011 Model Boats Construction Special, Richard Simpson wrote a superb item covering this very tricky, yet often overlooked subject. It is one of those subjects which only comes to light when a problem is encountered. I'm not sure whether the magazine is still available.
 
I struggled with the stability of a paddler model some years ago, tried everything, building a lightweight superstructure and upperworks, moving the lead and batteries etc. In the end I gave up, decided to cut my losses and scrapped the model. Now wish I hadn't as the answer was staring me in the face - add a lead torpedo type keel, which needn't be anything like as deep as the ones fitted to yachts (not meaning that this would be your answer).
 
Tony
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pintheair

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Re: help with stability
« Reply #4 on: September 14, 2013, 03:25:25 PM »

so, you seem to think the centre of balance is too high,
 i need to get  the weight down lower,  there is no keel to speak of below the hull ,
 maybe adding one might help also help.
thank you,   i will have a go soon ,







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just let me modify it a bit

condeh

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Re: help with stability
« Reply #5 on: September 14, 2013, 06:37:31 PM »

There are only 2 things you can do to lower the amount you heel in a turn.


1) go slower. (not always practical of course)


2) lower the Centre of Gravity.


if the boat feels tender anyway, then lowering the CoG is a good idea, otherwise a stiff gust of wind may well be the end!
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