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Author Topic: Scale speed advice...  (Read 1268 times)

Lash151

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Scale speed advice...
« on: January 17, 2012, 03:41:19 PM »

Hi... I'm new here so forgive me if I'm in the wrong section!  I am in need of a bit of advice regarding what motor/gearbox and prop size I should use in a scratch built fishing boat...
Its a 1/16 scale model of a Chesapeake Buyboat, which is one of these... http://www.oysterbuyboats.com/   Its basically a fifty foot wooden fishing boat with a diesel engine.
The model is about 900mm long.

Could some one hazard a guess at what motor/gear ratio and prop I should be looking for to get close to a scale speed? 

I am getting back into model boats after a ten year break, I have picked up where I left off, with a half finished plank on frame hull and a set of plans!!  I need a bit of help getting my brain working again!! 

Cheers Lee
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Bryan Young

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Re: Scale speed advice...
« Reply #1 on: January 17, 2012, 04:35:37 PM »

This has been the subject of much discussion in the past...no criticism intended here.
But why do you want to limit your models speed to a "scale" speed? With modern speed controllers you can drive at the speed that seems suitable for your boat. This has the great advantage that you will have power to spare so enabling you to accelerate out of "trouble". It would also give you a lot more "oomph" when turning, as all models (and the real things) lose a lot of speed in a tightish turn. Just a thought.......BY.
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Lash151

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Re: Scale speed advice...
« Reply #2 on: January 17, 2012, 06:52:58 PM »

Hi... thanks for the reply... thats an interesting angle.... I shall think about it!
Sorry for asking the 'forums most annoying question'   :embarrassed:
Lee
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Tug-Kenny

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Re: Scale speed advice...
« Reply #3 on: January 17, 2012, 07:57:53 PM »


Hi Lee and welcome to Mayhem.

No it's not an annoying question at all.  I have moved your enquiry to the motor section as you may get more help here.

cheers

Ken
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Subculture

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Re: Scale speed advice...
« Reply #4 on: January 17, 2012, 08:46:32 PM »

Scale speed is calculated by taking the fullsize boats speed and dividing it byt square root of the scale of the model, in this case that will be four.

What's the scale speed of a boat like this- somewhere between 10-15 knots? So somewhere betwen 2.5- 4 knots or thereabouts.

Shaft speed depends on prop size and pitch. I'd be inclined to go with the largets prop I can fit in the confines of the hull.

Most props designed for electric drive tend to have a pitch range of about 1.2-1.4 times diameter. To work out speed in mph, assuming 25% slip-

RPM x prop pitch/1408
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