Towards Building a Steam Powered Outboard Motor

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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Elver1
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Towards Building a Steam Powered Outboard Motor

Post by Elver1 » Tue Nov 15, 2022 2:57 pm

Building a steam powered outboard motor has been a really long term interest for me -- dating back a couple decades to the first time I read about Terry Williams Sprite engine. Since then I've built two lathes from scratch, an oil fired iron melting furnace and many other interesting projects, but never attempted the steam outboard. I bought Benson and Rayman's Experimental Flash Steam 20 years ago, Westbury's book, too, read them many times through and pored over decades worth of ME's for flash steam info. At 73, it feels like now or never, because I'm sure building something that works reasonably well is going to be a long process for me.

At the moment, I'm still thinking about it and finishing up house chores before winter (splitting wood, tractor winterization, mounting the plow, etc.). But I still can try to focus evenings on just what I should do for a project. Even after all this time, it seems to change every few hours that I do think about it! So I need to stop thinking -- I just have to start simple, with a small engine, and see what it does, and what I get. That will give me a better idea of where I want to go from there.

Here's some "in general" thoughts about what I want for a steam outboard motor:

I imagine something that can power my lightweight 1958 Crestliner aluminum 14' skiff for what I do with my family: camping, fishing and exploring. The boat doesn't have to plane, though that would be interesting if possible. Presently with family of three aboard, a Mariner 8 hp OB planes it fine.

On the other hand, reaching non-planing hull speed - say 5mph - takes maybe a .4 kW using an electric trolling motor. So for that situation steam outboard of 1 hp would likely be reasonable, but I'm thinking maybe 2 hp if caught out in conditions you didn't mean to be in, bucking a headwind.

I'm thinking cast iron for both piston and cylinder, since I can cast those myself, though I could go with aluminum piston and cast iron rings in a CI cylinder, or I suppose it could even be a steel cylinder if there was a reason for it.

Arbitrarily I'm thinking something around 2" bore and stroke. Single cylinder, single acting, enclosed crankcase. Poppet or piston valve inlet, cam driven, uniflow exhaust. Monotube, wood fuel.

But first I'm thinking about making a smaller stationary version maybe, 1" x 1" engine. It's important for me to actually start something physical. I can think about something forever, and it just becomes a rabbit hole of inaction. I want to hold in my hand a piece of metal in the shape of a motor, no matter how well it fits to my ultimate expectations. That's the real start.
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barts
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Re: Towards Building a Steam Powered Outboard Motor

Post by barts » Thu Nov 17, 2022 6:07 am

Some random comments and thoughts based on my experiences:

Some 35 years ago I converted a small cast-iron industrial refrigeration compressor (twin cylinder 2" x 2" ) to steam by adding a new head and steam chest, plus a rocker arm and slip eccentric for reversing. This went into a 19' wooden boat, and powered our steam adventures for many years until the main bearings finally wore out.

The lubrication issues with the enclosed crankcase were annoying; one really has to run something like steam cylinder oil and water mixture. I would have been better off using a small twin cylinder 4 stroke engine with oil control rings, if such a thing could have been found. Alternatively, using the original pistons as the cross heads and using distance pieces to mount twin double acting cylinders above the existing ones would have worked well. Many high speed generators in full size steam ships used such a configuration.

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.

The advantages of a more efficient plant are difficult to realize at our small scales - the surface area to volume ratios are all wrong. Good insulation may be more effective than ostensibly better designs.

There's a neat steam outboard running around in the Pacific Northwest, attached to a canoe. The boiler is propane powered, and is inboard, the engine mounts side saddle where it's easily adjusted and a steam hose connects the two. When they get back to the launch area, the canoe goes on top of the vehicle, and the boiler and engine go in the back.

A cast iron cylinder with cast iron rings and piston are likely best from a wear perspective; slide valves are best made of bronze running on a cast iron valve plate.

Piston valves w/o rings don't stay steam tight very long, and require precision work to renew. Slide valves are easily made and wear in rather than wear out, and the wear surfaces are easily remade. Yes, they're less efficient, and result in more valve train wear.... they do seem to work well made relatively small, and driven with a slip eccentric, which works well on a single cylinder engine, and saves complications and weight.

Engines that run in salt water will end up looking pretty ragged unless completely protected from salt spray - difficult in open boats, or meticulously maintained.

If you run only in fresh water, forcing the boiler with the engine exhaust can really boost steam production. Locomotives, of course, relied on this.

A one hp single expansion (30%-50% cut-off) steam engine at 120 psi or so will use about 40 lbs ( 5 gallons) of water per hour.

Good luck - lots of stuff to figure out!

- Bart
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Bart Smaalders http://smaalders.net/barts Lopez Island, WA
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Re: Towards Building a Steam Powered Outboard Motor

Post by Elver1 » Thu Nov 17, 2022 1:48 pm

Thanks Bart! :)

It will be fresh water only, assuming it ever is workable. Probably cam driven poppet valve intake and uniflow exhaust. Right now, I'm starting to draw a smaller experimental version with 1" bore, SA, single CI cylinder and piston, poppet valve, cam driven.

If that doesn't work out well after fooling around with it and finding what problems I can invent for myself, I can change any or all of the above. :)
I'm thankful for all suggestions and input!

The modified 4 cycle engine with piston extensions using the pistons as crossheads was also used during the world war in England to modify a tractor if I remember correctly -- think I saw it in an old ME.

I have built in the past a rotary valve steam adapter head for a 4 cycle IC horizontal engine, and from scratch a very small uniflow cam driven piston valve SA single from CI pipe fittings, steel pipe and nails. That was just as a fun challenge to see what could be done with very limited materials. I agree about the wear problems for these valve types.

I also own a couple of homemade model aluminum enclosed crankcase SA twins with slide valves, and have done a few similar engine case castings in CI. I do like twins and slide valves, I'm just right now going to start out with the above to see what happens if I do.
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Re: Towards Building a Steam Powered Outboard Motor

Post by Elver1 » Fri Nov 18, 2022 3:28 am

For the little experimental engine, my current thinking is a 1" x .75" cylinder and block cast as one. Just a simple pattern on left with machining allowances and, without cores. Machined from solid on right. Bearings would be carried in end plates bolted on. Sides are rectangular to allow mounting pumps in a compact fashion.
1x15SCEngineBlock.png
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Re: Towards Building a Steam Powered Outboard Motor

Post by barts » Fri Nov 18, 2022 3:56 am

What kind of RPM are you considering? What sort of rod bearings?

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Re: Towards Building a Steam Powered Outboard Motor

Post by Elver1 » Fri Nov 18, 2022 2:11 pm

Bart, for me it's something new, and an experimental engine, so as possibly naive but hopeful thinking, I'd like to get to about 3000 rpm on this small engine. And at first plain bearings, but could be needle on the big end, if it had to be. I'm going with overhung crank with follower for the pump drive. In all this I'm borrowing heavily from model racing hydroplane practice, and especially indebted to the Westbury/Spartan, Kirtley/Pisces, and KBC/OOYA lineage. But for milder performance expectations and use, of course.

This little engine isn't intended to be the outboard, but just part of the learning process leading there. It's about half scale in size and therefore about 1/8 the power.
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Re: Towards Building a Steam Powered Outboard Motor

Post by PeteThePen1 » Fri Nov 18, 2022 8:06 pm

Hi Elver

Just a sideways thought for you. Do have a look at the twin cylinder engine that Dietrich has designed and nearly finished building:

viewtopic.php?f=8&t=2405

It is a nice elegant design and possibly small enough for the task you are suggesting.

Regards

Pete
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Re: Towards Building a Steam Powered Outboard Motor

Post by Elver1 » Fri Nov 18, 2022 9:16 pm

Gluing up the pattern.....

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Re: Towards Building a Steam Powered Outboard Motor

Post by Elver1 » Fri Nov 18, 2022 10:22 pm

Pete, that's a very nice engine, beautifully made.
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Re: Towards Building a Steam Powered Outboard Motor

Post by Elver1 » Sat Nov 19, 2022 7:56 pm

The pattern:

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