Gas Engine Gearbox

by Martin Plumer
(Sydney, N.S.W. Australia)

I am in the process of building a model of our local ferry boat. It will be powered by a 26cc petrol/gas engine, but I can't find any gearboxes for that type of engine. Can you get forward and reverse boxes for model boats.





I'm hoping this is a big boat, because that is a big power plant in the realm of scale models.

The simple answer is: No. To my knowledge, there is no commercial gearbox specifically for model boats that provides forward, idle and reverse for combustion engines. However, there are a few workarounds.

  • Water Jet Drive

    A water jet drive system is a full-size solution to the problem you are asking about. It has also been duplicated in scale models and there is at least one commercial unit by Graupner. They call it the JET Booster-5 (SKU: 2347) for electric motors or gas engine up to 30cc. Depending on your skill level and tools, you could potentially make your own.

    The principle is to have the motor generate a stream of water shooting out the rear. By the articulation of a steering nozzle, the water stream is manipulated left to right as desired, for steering.

    A reverse flap can be brought across the stream to partially block it. In doing so, the flap is forcing the stream to do a u-turn and the resulting force is pulling the boat backwards. If the reverse flap is partially closed, and the resulting force is split even forwards and backwards, the boat will be in a state of idle.


  • Kitchen Rudder

    A Kitchen rudder is a century-old solution to the same problem, mostly used for slower speeds, so it may not apply. There is little sense in me explaining, Wikipedia is doing a fine job.

  • Gas Electric Drive

    Build a system, not unlike the electric system of a car or motorcycle. Have the engine turn a generator or alternator that charges a battery. From the battery you draw current through a regular ESC to electric motors that propel the model boat. It may sound complicated, and it is. The benefit over strictly electric is if the boat is big (and it better be to take a 26cc gas engine), the batteries can be relatively small and weight will be saved. At least that’s the theory. The alternator could come out of a car or motorcycle.


  • Electric Drive

    At the end of the day, a gas powered option has to make sense as compared to an all electric solution. The one advantage, that can’t be stressed enough, is its absence of noise. An electric powered model boat doesn’t disturb wildlife and fellow human beings the way combustion engine powered models do. Motors and ESCs for big boats can be found wherever Robot Wars components are sold.

Personally, I'd go with a Graupner water jet system for the gas engine. Otherwise an all electric drive is awfully convenient and therefore always my first choice.

Best of luck with your project!

Comments for Gas Engine Gearbox

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by: Petter

Sorry Emily, I don't do Facebook. I admit, I know nothing about pushing barges. Sometimes you learn best by trying things. Don't let me, or anyone else, talk you out of the ideas you believe in. Best of luck to your venture.
Gas motor on 4 prop towboat.
by: Emily JoAnne Shelton

If you would like to see photos of the boat. Message me on Facebook. My name is the same as I put it on here. I am wearing a black dress in the photo. Just mention this post thread so I know how you know me. Thanks.

The barges are mainly in my area used for field crops and sand.

by: Petter

What are those barges?
Gas motor on 4 prop towboat.
by: Emily Shelton

I want the power to move 4 props on a 46" towboat. The towboats around here push 15 barges and more when they go down river. I plan on building 15 to tie in front of it.

As far as the trans goes. I would like to find a metal case to replace the plastic one Tamiya uses. They already offer metal gears to go in it. Those semis have a hell of a lot of torque already. They can pull a car with ease. I just want the metal case to contain the rpms that this motor will have.

by: Petter

I like the idea of using the Tamiya truck transmission. However, I doubt it'll last very long. The difference in power it is sized for vs. what you're planning on putting into it, is probably an order of magnitude. I would try a much smaller motor. Preferably low RPM, such as a model diesel engine like the ED Viking or Taplin Twin Marine. Unfortunately neither is in current production. There may be some model diesel marine engines manufactured in the former Eastern Block countries, but I'm not familiar. There are ways to convert airplane engines to marine, but it can be pretty involved. You need to manufacture a cooling jacket for the cylinder and top. PAW in the UK manufactures model diesel engines for airplanes.
Technicalities aside, sounds like an awful lot of power for a tow boat, unless I'm missing something.
Gas motor on 4 prop towboat.
by: Emily Shelton

I was thinking of some how attaching a Tamiya 3 speed gear box from a 1/14 semi to a 26cc motor. That will give it 3 speeds forward & reverse. I just don't know if the trans will take a 6hp motor. I am going to be making my motor a hybrid using Arrow Shark items on eBay. Including their dual prop conversion. My towboat uses 4 props on 2 motors. I am going to run all 4 on one trans.
Gearbox
by: Fred

You may find something by researching steam links. It was the same problem for single cylinder non-reversing steamers. A "in and out" gearbox doubled and/with the addition of an idler for reversing and a shift fork controlled by an electric solenoid or servo. No synchro involved, just stop/shift/go. If the clutch is intact on your engine it takes care of stopping gear rotation to shift. Just an idea that I had for an old tugboat but moved on to other things. Good luck.
Reverse Gearbox for IC Engine
by: Richard Hallett

I have the same dilemma and I know all the alternatives BUT sometimes One wants to do...what one wants to do..and to this end I am working on such a project.

WHEN it will come to fruition who knows, but one thing is driving me forward.. I've built the hull (5'6" long) and installed the engine so it can't be that far away!

Unfortunately, other "projects" get in the way but I'm rather determined to crack this one. Sadly commercially available components are elusive, if at all, which delays even more, but watch this space!.

Richard, Wolverhampton, UK

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