Small steam tug

[rolphill]

I've spent the past couple years building a steam engine and boiler. I originally intended them to go in a go kart shaped object, but after some bench runs, I've decided the boiler is a bit too finnicky, temperamental, and low power to perform well on a land vehicle. So I've decided to try to put it in a small boat this winter.

The engine is a two cylinder, 1.5in bore x ~1.5in stroke, hackworth, with piston valves of my own design. It uses viton or silicone O-rings and ball bearings everywhere except the eccentric, which uses a 3d printed sleeve on the eccentric bearing surface and aluminum strap. It's almost all aluminum, made on a HAAS cnc mill. Not a single part was made on a lathe. Slitting saws, threadmills, keyway broaches, etc. It's a little bit on the big side for this boiler, but it's hard to tell on the bench without a load to slow it down.

The boiler is based on the clishay live steam locomotive. It's got about 2.5 sqft of boiler surface, and about 20 feet of 1/4in (~1.2sqft) superheater. It could still use an economizer coil in the top though. The central drum is a 3.5in diameter mild steel commercial pressure vessel of some sort with a flange on the top. Then there are two coils of 5/8in copper tubing wound around it bolsover style and silver soldered to into the drum. It uses the clishay firebox right as designed out of the book. I originally tried firing it on coal, but I had issues with grate clogging, and I think it runs better on wood pellets anyway. 100PSI max.

There is more info on the boiler here:
https://www.homemodelenginemachinist.co ... ghy.35874/
https://www.homemodelenginemachinist.co ... ild.36176/


This is the most recent (and most successful) bench run. After going back and doing a frame by frame it looks like the engine was doing a little over 500rpm here. My design goal is 300rpm, though.


I have low expectations as far as speed goes, but if I hit 3mph I'll be thrilled. After all, half a horsepower is still the power of like 3 people rowing, or a small trolling motor.

[rolphill]

I've now got the engine and the boiler to the point where I need to start working on the boat itself. The intended hull is a small old 14ft aluminum v-hull fishing boat. Last year my FIL gave us his old 14ft aluminum v-hull. All the wood was rotted, and normally it would've been easier to ditch this boat and find a more shapely one in better shape, but this boat has a big advantage many of you will understand:

This is my wife's childhood fishing boat, so she has a lot of nostalgia attached to it. This translates to significant leeway in time and budget to get it back on the water.

So far I've stripped all the rotting wood off, wire wheeled all the paint loose enough to come off on the inside, then primed and painted the inside.

In the meantime, I was bored at work last week and starting thinking about the propeller. I don't want a paddle wheel, as they are big and bulky, and it's a lot of fab work compared to the mostly machining work of a propeller and stern tube. I looked at APC propellers, but didn't really see anything that wouldn't be a compromise. So I ended up deciding to make my own propeller to save $25have the pitch and size I needed. I found a propeller cad model generator online and created a 12in x 20in propeller, targeting 5mph at 300rpm.

It was a huge pain (and took about 5 hours of machine time per blade!) but in the end it turned out well.

IMG_1464.jpg (183.06 KiB) Viewed 1076 times

After rounding the ends and sanding smooth, it turned out pretty good. I put it on a cordless drill and stuck it in a kiddie pool and it generated significant thrust. I don't like the hub so I think I'm going to 3d print a more hydrodynamic shroud for it.

That's about as far as I've gotten. Next step is to put new wood on the boat. I would like to get the hull in the water with a regular outboard this fall, then work on installing the steam engine over the winter.

[PeteThePen1]

Hi Rolph

Thanks for posting the updates. You have a lovely shaped hull there that should drive very easily. I am also impressed by the speed and efficiency with which you have designed and created a propeller. It put me in mind of my late friend Chris who built a launch based on a sailing dingy hull. He called it Maid of Scrap not least because he was a small business man who was notionally in the engine re-building trade but because of his ingenuity most of his work ended up as cutom made metal solutions for the firms in his locality that needed soutions quick. He made just about everything in the boat except the engine and the prop. You are clearly a 21st century 'fellow traveller' so I look forward to see your ongoing progress.

Regards

Pete

[fredrosse]

A simple propeller setup can be had with only one small hole in the transom. Engine shaft pierces the transom, then a Dewalt right angle drive (or similar drive sold for electric hand drills) , then another, then a 5 to 7 inch prop.

A small boat can be maneuvered with a kayak paddle, so no rudder nor reversing of engine is required.

It can be setup so the exterior assembly can be rotated to bring the propeller up and allow operation in shallow water with paddle only.

[rolphill]

First I'm working on making another pair of blades and hub, so I can make a four blade prop. I think I'm just going to start by putting the stern tube as low as I reasonably can, and if some of the prop sticks out of the water, so be it. A swiveling stern drive is a cool backup idea, although sealing the swivel joint sounds like a minor design challenge.

The other engineering challenge I need to deal with is metal compatibility. The hull is aluminum, so I'm assuming I can make hull penetrations out of aluminum as well. The boat will only be used in fresh water for relatively short durations, so should I use mild steel bolts or stainless steel bolts? I also have to decide on if I want to use stainless steel or case hardened chromed steel shaft rods for the prop shaft. Both can be had in 12mm for fairly cheap on amazon. I'll definitely use a mechanical shaft seal, as they are cheap and have much lower friction than a stuffing box.

Also, what's an easy way to insulate small diameter steam lines? I was thinking of just wrapping them with cotton clothesline rope, then maybe covering with aluminum tape? Fiberglass is messy and annoying, especially for things that will be removed from the boat and stored inside.

[Lopez Mike]

As to insulating pipes, I would follow the advice I received from Bart.

Wrap the pipe with 100% cotton cord. Then paint it with Titebond 3 wood adhesive suitably thinned with water. When that is completely dried, Paint to suit.

Mike

[Lopez Mike]

Making this a separate post.

I suggest contacting Russ Noe (active on this forum) to have a good long look at his sailboat conversion. He lives in the Hood River area. Do NOT be put off by his workmanship. He has created a show quality boat. A bit lower standard of detail will work just fine.

Mike

[Lopez Mike]

Forgot to mention. I strongly recommend attending any and all of the NW Steam society events. You will get all of the rides you could wish and probably a bit more advice than you are ready for.

Mike

[RNoe]

rolphill:
Lopez Mike is being too kind. (Thanks, Mike!)

You can find info on my project Cluaran on another thread here:
viewtopic.php?t=2211

And you are welcome to visit me for an inspection of The Boat in person.
Just contact me via Private Messages.
RussN

[rolphill]

Unless there's something happening in west MI, I don't think I'll be able to attend.

In the meantime I've got pretty much all the wood sealed and ready to get put on the hull. A local farm store sells stainless steel bolts by the pound, so I have to pick up a bunch of those next paycheck. In the meantime I ordered 12mm stainless steel rod, a flexible coupler, and mechanical shaft seals for building the stern tube.

I machined two more blades, and I'm working on the stern tube and hub and such.

Screenshot 2024-09-16 080408.png (38.85 KiB) Viewed 68 times

The stern tube uses a 3d printed bearing, and a standard mechanical shaft seal.