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Feb 27, 2005, 11:48 PM
Thread OP

Building an RC Boat from scratch

Hey all,

Would anyone know of some resources they could suggest that discuss how to build a RC boat hull, from scratch? For example, that detail how to design the hull structure, and how to build engine mounts, or thru-hulls for propulsion?


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Feb 28, 2005, 12:15 PM
Useful Idiot
The Complete marine Radio Control Manual if it's still available was pretty comprehensive. It rather depends on what tyoe of boats you're interested in.
Traplet in the UK do quite a number of titles.
Feb 28, 2005, 06:13 PM
Thread OP

Thanks! More q's...

Cool, thank you! I'll check them out. I suppose the hardest thing to know is where to balance the center of gravity, to get good planeing. What worries me are the thru-hulls; to make sure the boat doesn't leak!

Oh -- what about selecting the right motor? Is there a weight to RPM or strength ratio to follow?

Thanks! --dave
Mar 01, 2005, 12:19 AM
Useful Idiot
A starting point for cg is usually about 30% of the boat length forward from the transom. So, say, for a 20" boat the cg would be 6" from the transom. Riggers and hydro's are a little different.
Stuffing boxes can usually be made watertight enough with just a little grease on the front and rear shaft bearings. It's fairly usual for there to be some seapage but that's not often a problem.
On the weight you need to build as light as possible, remembering that electric- powered hulls don't have to put up with the same vibration as their i/c brethren. The 20" example I gave would probably take a car motor, 6 or 7 sub C cells and should weigh complete about 2 lbs.
Mar 01, 2005, 02:05 AM
CG Bob's Avatar
what about selecting the right motor? Is there a weight to RPM or strength ratio to follow?
Are you building a model of a full size boat, or copying some design features from other models the same size that you want to make yours? If you're copying various design features from other model boats, find out what they are using in those hulls. If you're building a model of an existing full size boat, you should have the following information: hull length; hull beam; displacement; shaft horsepower; and design speed. If you have that info, you can figure out the model parameters with some formulas.

First is the scale of the model, say 1/48.
Second is the Scale Factor - the cube of the scale: 48 cubed is 110592.
Portotype SHP: 5000 hp
Proto Watts:3,740,000 (5000 x748)
Model Watts: 33.8 (Proto Watts/Scale Factor)
Watts X Scale (loss) Factor: 38.9 (Model Watts X 1.15)
Current @ 6VDC: 6.5 Amps
Current @ 12VDC: 3.25 Amps

Proto Displacement: 1000 Loong Tons
Model Displacement: 20.3 pounds
Mar 01, 2005, 03:22 AM
Useful Idiot
CG Bob, I took the reference to "good planing" to mean the interest was for something a tad lighter and faster than true scale
Mar 01, 2005, 12:42 PM
CG Bob's Avatar
You may be right, but the formula for prototype hp to scale watts is a good satrting point for the model motor or engine size. The example I listed in my calculation is for a USCG 210' Medium Endurance Cutter with twin shafts. For a scale wake, the model speed over GROUND will be faster than scale speed.

To calculate the "model" hp needed using my example:
Model Watts/748 = model hp - 33.8/748 = 0.052 hp
Proto SHP/Scale Factor = model hp - 5000/110592 = 0.0452 hp
Mar 01, 2005, 09:26 PM
Thread OP

Here's a shock...

Originally Posted by CG Bob
Are you building a model of a full size boat, or copying some design features from other models the same size that you want to make yours?
Hrm. Well, I'm not sure how to say this without sounding like a lunatic, but we're building a solar, gps-guided boat to circumnavigate the world. Our website is at We don't have a boat plan yet, but we're working to draw up a prototype 3-D model "as it's in our heads" and then apply it to more practical designs.

However, it's essential to get across that the project is far more than a challenge; really, it's designed (well, we're currently designing it!) to be a classroom teaching vehicle, to give students in K-12 science classes a chance to provide meaningful input (what teaching theorists call "Legitimate peripheral participation") to a nifty challenge. This is, above all, the reason for taking on the challenge.

At the moment, we're in the planning and feasibility stages, so I'm going through the motions of learning what challenges we'll face. After that, we're going to recruit some people from local schools (MIT is down the street, for example) or, for that matter, from anywhere at all, and get crackin'

We'd be interested in any & all feedback =>

Mar 01, 2005, 10:46 PM
CG Bob's Avatar
After reading the info on the Naultilux website, you may want to consider a dispacement type hull rather than a planing hull. It appears that you are not looking for high speeds that planing hulls are known for; you just want to be able to overcome the current, and manuever the boat. Planing hulls are designed for speed; examples are PT Boats, USCG 41 foot utility boats, and hydroplanes like Miss Budeweiser. Displacement hulls have greater capacity; examples include destroyers and frigates, freighters, tugboats, and tankers. A displacement hull of some sort would be better suited to carry the motors, battery backup, GPS gear, recorders, radio, etc., that you might want.
Mar 02, 2005, 12:10 AM
Useful Idiot
There's nothing infeasible about the plan. A GPS controlled model plane has crossed the Atlantic with an i/c engine. There was even mention of it in the "life, the Universe and Politics" section of this site. See
I would agree that a displacement hull is needed. The sort of energy requirements for planing hulls just aren't going to be available through Solar cells.

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