Towards Building a Steam Powered Outboard Motor

[Elver1]

Twenty mile an hour gusts yesterday below freezing, and 15F this morning, so I haven't been able to get set up to cast yet. I have to get my sand indoors and conditioned today. Winds predicted for this afternoon as well. But we'll get there at some point this week.

[TahoeSteam]

You're moving quickly! Got about the same conditions up here today. Where abouts are you?

[PeteThePen1]

Nice pattern! Pattern making has always appealed to me as a special form of wood working. However, having no access to local iron foundaries I have never gone down that path. Good to see it done well.

Regards

Pete

[Elver1]

Wesley, I'm in Vermont. I always think of California as warm! But, never been there, believe it or not. Thanks Pete, I like making patterns and casting a lot. But I haven't done it since early last spring, so I have to get my stuff all back in shape to start again.

I did get a box full of the sand indoors -- about 35 pounds of it, and got some moisture in it (3%), it was completely dried out. Wind hasn't been as bad today as predicted. I probably could have cast. But I don't want to rush it first time this fall. I think I'll light the furnace, though, this afternoon and make sure it's heating right. And crush some coal to make up new facing sand. And just generally clean up the casting area. It's an outside lean-to roof so leaves get blown in in the fall. But, you know, it's exciting to do something again even just getting ready.

Probably the first attempt with this pattern will have problems. It's kind of massive, and coreing it would have been smarter. But I decided I'd rather machine it from a block instead of boring out core scale, or dealing with possible chill spots from variations in thickness for this particular deeply hollowed part. We'll see. The main possible problem is likely to be excessive shrinkage, since I only allowed 1/8" -- that was probably optimistic. A big riser will help, but I have somewhat limited capacity crucible. We'll see how big a riser I can fill...and still pour the part.

[Elver1]

Couldn't cast today, but this evening I was able to draw the engine front plate/bearing housing and a pattern.

Pattern3.png (39.69 KiB) Viewed 19165 times

[fredrosse]

From Barts: "A uniflow engine is attractive from an efficiency standpoint, but needs good vacuum if the clearance is to be kept low - and any clearance directly affects efficiency. This would make starting such an engine, especially on an outboard, tricky."

Barts statement is all true, however it gives the impression that a uniflow engine would be troublesome here, requiring a condensing/high vacuum exhaust system.

The uniflow engine used on my domestic heat-power system, and now mounted in a steamboat, has always run with exhaust at atmospheric pressure. This engine is considerably more efficient than typical counterflow steam engines, and is far easier to start than a similar size typical gasoline engine. This is because the "compression ratio" (a term usual to the internal combustion engine world) is only about 4:1. In steam engine jargon, that translates to a "clearance volume" of something more than 22%, which would generally be considered abysmal for typical steam engine practice, where low clearance volume is usually an important design goal.

In this case, yes, the high clearance volume of my uniflow engine is detrimental to efficiency, however the advantages of the uniflow arrangement (plus some other design features) allows this engine to have steam consumption rates much better than the great majority of steam launch power plants. This uniflow engine has tested at 21 pounds of steam per horsepower-hour output, whereas most launch steam engines consume about double this steam consumption rate.

The engine has a “clearance ring” which forms extra clearance volume in this engine, so the clearance volume can be easily adjusted. The attached picture shows the gap for the clearance ring, mounted between the cylinder head and steam cylinder flange,

[Elver1]

Just got through pouring the crankcase/cylinder casting. Now the long wait.....

[Elver1]

The rough casting hot out of the mold. Some shrinkage but it looks like it's all probably within the machining allowances. I took a file to the corners to check for hardness, and it's gray iron. That's good because one of the ingots poured had a fair amount of chill when broken open. But it was a thin piece and poured into a cold metal mold.

So, all in all, actually an acceptable casting first try this fall.

[Elver1]

Thanks for the explanation and photo of your engine, Fred Rosse. Very interesting. I also remember reading somewhere that uniflow engines liked some clearance volume.

Is the base of your engine from a compressor? I was trying to figure out what the flywheel was, such an odd configuration. At first I thought it was part of a generator for your CHP setup, But now looking at it I think it's probably a repurposed cast flywheel/cooling fan, with a sheet ring around it to stop the blades from working, since you don't actually want cooling on a steam engine.

[Elver1]

Squared up :