.21 Nitro on 28" Balsa Hydro?

[dmc456]

I'm building Dave Frank's OH BOY! OBERTO 12 CELL SPORT HYDROPLANE except i'm going to use a Nitro Engine instead of electric.

The boat will is only 28" long and estimate the weight to only be about 3 lbs minus the engine.

I am about 1/2 way done with the balsa hull. I have come to the point where I need to decide what engine to use. I was considering the Megatech .21 high performance marine engine which is supposed to have 2.1 HP and 28,000 RPMs.

What do you think about this engine. I can get one pretty cheap. I'm looking for something that will really move. I'm looking for input on engine selection. I think this engine is plenty large, but want to make sure it isn't too large. I know it will fit or I can make it fit in the boat.

I have attached one of the pics on Dave Franks pics so you can see what boat I'm talking about.

[dmc456]

Here is a pic

[dmc456]

Another of Dave Frank's Pics

[Ron Olson]

You'll twist the boat apart trying to run a .21 in it. Try something a little smaller like a .12. It is lighter, cheaper to buy and run, most of the driveline parts that you need are basically the same as what you'd need for the electric version. You can pick up a decent .12 for the same price as the Megatech. I bought a Fantom for $129.00 that puts out almost 43,000 RPM and 1.6 HP.

[haljmac]

I agree with Ron. You are building with balsa, why is it so heavy? I have built hydros similar, to what you are building, installed the cmb 21, and it was under 4lbs complete with engine and hardware. I use 3/32" 5 ply plywood for the rails and transome and skinned it 3 ply 1/16" plywood. My opinion is that balsa just is not strong enough for marine.

[haljmac]

pic

[haljmac]

pic

[dmc456]

Thanks for the feedback. I'll try a smaller engine than a 21. This if my first boat project. I have done planes and a heli in the past but don't have a good idea what size an engine to use.

Not sure what the boat will weigh either. I think the finished electric version is around 3.5-4 lbs.

My plan is to build the balsa frame / shell and spray it with an epoxy paint on both sides for stength and water proofing.

[dmc456]

Where can you find good high performance .12 and .15 engines. I was looking at tower hobbies and they don't really have anything with RPMs.

[hydroracer]

any rear exhaust nova rossi .12 with a rotary carb would smoke. tower has them

[Spraguepsycho1]

wouldn't it be risky using an air cooled buggy engine in an enclosed boat canopy? I haven't been able to find a powerful watercooled .12 or .15 engine on Tower's website either(or anywhere else online for that matter), but my engine should get enough airflow over the buggy .12/.15 heatsink head to keep it from burning up.

[Ron Olson]

I currently have 2 boats, an outrigger hydro and a mono that both have air-cooled .12 engines. They are both pretty open to the cooling air, so much that on one I've cut some of the cooling fins off from it. They actually get cooler not to mention moister air than the engines confined in a body. The heat sink would have to stick out of the cowling unless you want to open up the front of the cowling somehow which you would have to do with any Nitro engine that is put into it.