Powering a Pilot boat model

by Manning
(Charleston, SC)

I am building my first ever wood deep vee static build model of a Fort Sumter Class Pilot Boat, using actual ships drawings. The construction is mostly pine and very thin plywood.

I'm think of powering the boat with a cordless electric drill/screwdriver as a motor for the boat. Has this been done, and do you think its a realistic idea?

I must say so far thing are going together pretty well. I'm just concerned I would not get to much run time from one of these screwdrivers, or maybe it'll get to hot.

I'd like to here your advice. the model is 4 feet LOA. about 10 inches at the beam. weight will be about 20 pounds. Its going to be big and heavy.

---

I'm not all that familiar with the Sumter Class Pilot Boat, but you said deep-vee, so it's a relatively fast, planing hull.

Also, I'll be honest, I've never built a boat with a planing hull as big and heavy as yours, so bear this in mind.

For a 4-foot planing hull, 20 pounds sounds heavy, so it'll take a lot of power to bring it out of the water and up on the plane. Having said that, anything you can do to cut down some of that weight will help in terms of speed, endurance and cost of motor plus batteries.

Most boats that I've seen similar to yours in terms of size and weight have had gas engines. Gas offers a good power to weight ratio while being comparatively cost effective. Many lakes and ponds are out of bounds due to noise pollution, so find out ahead of time if your location is OK for gas boats.

As to using the cordless drill, it won't be fast enough with its gear reduction. The fastest it'll probably go is in the range of 500-750 RPM.

The boat you're talking about (I'm guessing) would need at least 8,000 to 10,000 RPM at 1-2 HP. This may sound like a lot for a cordless drill motors, but a DeWalt 24V hammer-drill motor peaks at 2HP and can be purchased directly from their website. You can also contact your local DeWalt repair shop and have them order it for you.

These motors come with a pinion on the shaft that you may be able to use, otherwise you need to be able to remove it.

To match your motor speed with your load you may need a speed reducer and/or play with several different propeller diameters and pitch. This process can be fun or it can be frustrating.

You mentioned over heating of the motor. This will be an issue regardless what motor you decide to use and is normal. The easiest way to deal with it is to install a simple water cooling system for the boat. Here is a short description of a classic solution:

1. In the hull, at the perimeter of the propeller (or very slightly behind it), you install a water intake. It doesn't need to be fancy, a piece of brass tube epoxied in perpendicular to the propeller shaft is fine. Some insist on cutting angles in the tube etc. I'd say make it flush with the outside of the hull. It needs to extend far enough inside to be able to mount a plastic tube over it. You may need to reinforce the hull to give the tubing adequate support.



2. Somewhere else on the hull, above waterline, in the vicinity of where the motor will end up, install a similar piece of brass tube for the outlet.



3. The motor casing needs a cooling jacket. A coil of copper tubing is probably the easiest way to accomplish this. Don't coil it directly on the motor. Instead, use something slightly smaller in diameter as a bobbin. Whatever you use has to be without end flanges so you can slide it off the end when done.



4. To install the jacket on the motor you can twist the coil "against" the wrap and it will open in diameter slightly. As you do this, slide it over the motor. If all works out well, as the coil springs back it will grip the motor. To finish it off, attach one or two hose clamps on top of the coil.



5. Connect the intake to one end on the cooling jacket and the other to the outlet using silicone tubing. The tubing can be found at McMaster-Carr for instance.

Every once in a while you may stumble upon high power DC motors on surplus websites, such as surpluscenter.com. Another tip is to investigate motors used in the Battlebot community.

I hope this answer will be of some help to you. Feel free to use the "comment" feature on this page for a follow-up.

Best of luck with your boat project!

Petter