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Nov 26, 2019, 02:58 PM
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stegla's Avatar
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Small boat questions, MM Runabout


Hi Guys,

I would like to make use of this small vintage diesel engine. It's an ED Baby 0.46cc. I've found plans of the model maker Runabout here on RC Groups. Do you think that this a good choice?

What might be the thread size on the prop-shaft? The propshaft diameter is .015" or 4mm.

I might need to find a smaller prop? A 1" prop is suggested on the runabout plans and the prop that I have is 1.5"

Attached is a photo of all the stuff that I have at the moment.

Steve
Last edited by stegla; Feb 02, 2020 at 01:53 PM.
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Nov 27, 2019, 05:32 AM
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Good old Model Maker design. Smaller prop will be required or you will cut a groove in the underside of the hull. With the ball coupling shown, would imagine the threads to be BA. Enclosed plan PDF and original article.

Regards Ian.
Nov 27, 2019, 11:16 AM
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Ian

Thanks for the links. Indeed, I'm sure that the shaft threads are 4ba.

A groove in the hull is a good idea if I can't get a 1" 4ba prop

Steve
Nov 27, 2019, 01:52 PM
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Steve Contact Simon at Protean Design and he will fix you up.
Nov 27, 2019, 05:27 PM
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CaptLee, thanks for the Protean Design suggestion, I'll give him a try.

Steve
Nov 28, 2019, 08:36 AM
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As an addition, DO NOT under any circumstances be conned into changing that ball joint coupling. NO end thrust is transmitted from shaft to engine or vickey verky. Non of the modern crap comes anywhere near as a replacement.

Regards Ian
Last edited by Circlip; Nov 28, 2019 at 08:41 AM. Reason: T'other bit mentiioned in original artical
Nov 28, 2019, 11:42 AM
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Ian, Thanks for the water skier plans- I'll save those for later..... if the boat runs nicely!

I fired up the ED Baby today. Once I found the correct settings, it seems to be an easy and willing performer- with very good compression.

I will have to make a custom prop-shaft tube... do you have any words of wisdom here? I have various sizes of brass tube at hand.

Steve
Nov 29, 2019, 05:51 AM
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No affiliation but these are worth a look https://www.modelboatbits.com/PROP-SHAFTS/

Whatever you do, use bushes in the end of tube to reduce friction.

Regards Ian.
Nov 29, 2019, 12:49 PM
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Thanks Ian,

One last question (for now). Do you have any ideas as to the best way to arrange a water pick-up? There is no mention on the plans as the motor on the original is an air-cooled DC Dart.

Shall cut some wood this weekend.

Steve
Nov 29, 2019, 02:39 PM
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Do you have any ideas as to the best way to arrange a water pick-up?

Usual is a tube a inch behind the prop. Get a 1/8" diameter copper tube, drill a hole through the keel, bring it down into the prop wash and bend the bottom so that it faces forward as a scoop.
Dec 01, 2019, 07:36 AM
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As dodgy says but the ones I've used are within 1/8" (3mm) behind prop with the hole just covered by the tip arc. Water is forced by the prop through the system so even if release is delayed, once in the water, cooling starts without forward movement and the outlet shows cooling flow or not in the event of a blockage.

Regards Ian.
Dec 01, 2019, 11:09 AM
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Thanks for the advice, I'm sure there will be space somewhere for the water pick-up!

I've cut the bulkheads and assembled the keel. I'll post a picture when there is a boat-like skeleton to show.

Steve
Dec 08, 2019, 01:07 PM
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Here's a picture of where I'm at.

Steve
Dec 08, 2019, 06:07 PM
///////
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Will it be R/C or free running?
Dec 09, 2019, 11:11 AM
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It will have r/c. Our model yacht pond has concrete walls.

Attached a photo of the model yacht pond St Peter Port, Guernsey.

Steve


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