Very very lightweight steamboat..Suitable engine?

[87gn@tahoe]

Well, I don't think that inertial loads will be too much of a concern if one builds with the proper materials.

I do like the idea of the chainsaw engine as a base. Our Husqvarna chainsaws rev up to 14,000rpm all day long (depending on the which saw of course) and last a long time. Those bearings will last literally forever in a relatively "low RPM" steam application.

[Mjolnir]

There is no particular reason why a steam engine of the same general proportions as the chainsaw should not turn at the same RPM, which is where inertial loads start to be a problem. If they weren't, the chainsaw itself could probably go even faster. The main reason we don't normally try to build engines that way is that it is harder to make efficient use of the power if it is generated at very high RPM. It is also a bit pointless making a very compact high revving engine when it still needs a boiler which will inevitably occupy quite a lot of space, generally much more than the engine. ( a monotube boiler can be made lighter than a shell boiler, but will still take up a lot of room.)

regards
John

[Maltelec]

If I were making a super lightweight engine it'd be a single with ball-race bearings all round and all out of aluminium except the cylinder liner and rings would be cast iron, as well as the valve face Simple as possible. That way the aluminium can be minimal while the bearings can be very durable. No need for reverse, take a paddle.

The boiler would be a flash steam type. No need for a valve or anything, just fire it with gas and regulate the gas supply. It should be so responsive that the gas valve will be almost an instant response to the steam supplied. A thin steel inner sheet to direct the flame and a thin aluminium outer to prevent burnt shins with an inch of insulation between would be more than enough.

A geared down (with a belt to save weight) double acting feed pump would allow the engine to rev fast without a clattering pump all the time. Remember to make the gearing an odd ratio to prevent harmonics.

Have the gas bottle effectively floating in the water in the boat. It'll keep the bottle warm and remove more mass out of the boat. It'll even add buoyancy as it empties as long as you tie it down.

Also think of things like a hollow prop shaft (though remember to block off the ends!), hollow or cup piston, venturi effect on the gas and exhaust so you can get away with a small flue and funnel, and above all, keep it simple.

[fredrosse]

Maltelec, my first "person size" steamboat was very similar to what you describe, a canoe with a "drop in" steam plant. The only "car top" steamboat I have ever seen.

The engine was made from a 4.7 cubic inch chainsaw engine crankcase, crankshaft & piston. Single acting, 600 RPM, about 1/2 horsepower. The boiler was propane fired, flash type made with 1/4 inch diameter stainless steel tubing, stainless inner casing, outer casing of aluminum over fiberglass insulation. Feed pump and 2 oil pumps were driven at low speed from small timing belts. It had an inboard/outboard propeller setup.

A complete description and pictures can be found at Radow's steamboating website:

http://www.steamboating.de/boats/sca-main-vortrieb.html