Small Steam Boat

I spent the last year or so building a steam engine with the intent of building a land vehicle. However after several bench runs, I decided that the boiler I built is a bit too temperamental and more of a handful to operate than I was expecting, at least without adding any automation. So I decided I want to put it in a boat instead.

Now, last year I built a tiny 10ft sailing dinghy, but the family obviously wouldn't fit in it, so it's nigh impossible to get several hours out on the water with it. However, 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 one that was 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.

It was pretty rough, but it held water without leaks, so it was time to start taking it apart.


I took a wire wheel to the inside, and got all the loose paint off. Most of the paint was still stuck fast though, so I left it and started putting a coat of bonding primer on.


That's about as far as I've got on the hull itself. As far as the engine goes:


If you're curious, the engine and boiler is better documented here:
Boiler for putting around in small dinghy. https://www.homemodelenginemachinist.com/threads/boiler-for-putting-around-in-small-dinghy.35874/
Trackless Locomotive Build https://www.homemodelenginemachinist.com/threads/trackless-locomotive-build.36176/


I have a bit of a unique situation where I have access to a large CNC at work and a small pile of scrap metal, but at home I have little hobby money and little free time. This results in unique situations like this week, where I decided to save $20make a propeller to match my engine.

The math says my engine will make about half a horsepower, so I needed an efficient low speed propeller. My propeller requirements are very similar to human powered kayaks and the like, and I looked at existing rc plane props, but I couldn't find anything really ideal. So I finally decided to machine my own propeller. I targeted 5mph at 300rpm, and used some propeller generator I found online to come up with this 12in x 20in design.

Machining this was a bit of a pain.


But it eventually came together. I still have to sand everything smooth yet and round the tips.


I'm not a fan of the hub though, I feel like it's going to have a lot of drag in the water. I think I might try 3d printing a small shroud to enclose all those angular surfaces.

Given the lack of power, and the fat hull shape, I'll be happy if I reach 3mph putting around the local lake. My stretch goal is to build a deck on the hull and make a little decorative(featherweight) cabin to make it look like a mini tugboat. Then I'll probably work on making a bigger boiler so I can go faster, as the engine could easily make 2+ hp with enough steam.

Besides working on the hull itself, the next thing to figure out is the stern tube. Obviously this hull originally had an outboard, but at least the transom is flat, so I don't need to conform to a weird angle. The major design consideration for the stern tube / stuffing is going to be minimum friction, as I don't have any power to spare.

I'd like to get the boat in the water before winter, but probably with a regular outboard. Then I have all winter to figure out the steam engine installation.

 

To me this looks like a good candidate for a sidewheeler. Put everything on a welded frame that simply goes drops into the boat and is secured to the gunwhales. You can see such an arrangement here on a folding kayak Faltbootbasteln: Dampf-Faltboot http://faltbootbasteln.de/fbb-dampf-faltboot.html
A propeller installation will require some form of thrust bearing secured to the boat. This kind of boat doesn't have a thick hull, so you need to rivet in some longitudinal framing to take the loads. The gunwhale needs rebuilding anyway, it's no problem making it sturdy enough. The engine/boiler frame will stiffen the boat transversly and it can float over the hull bottom. Plus you can remove the whole thing as a unit and use the boat with an outboard.

One of our forum members has a very nice sidewheeler, I hope he drops by this discussion

 

Going to agree with Rumars on this, hanging a 12" prop with its assorted stuffing box and strut(s) under a shallow hulled boat is not going to be an easy job, and the thin sheet metal will offer little support for the struts.
A sidewheeler will be more suitable for that hull.
Many years ago, I built a 4" bore, 8" stroke vertical engine with Stephanson valve gear.
I planned to use it in a sternwheel boat.
Alas, sometimes life goes against your plans.
Steam is wonderful.

 

I think your first step should be to make sure the engine boiler or pipes won't explode. This was a common cause of casualties. Second, calculate the weigh of your family, supplies and steam engine. The total weigh should be no more than the maximum the boat is rated to. If the rating plate is gone, that is a common type and you can look at a similar hull. Also, a steam engine generate a lot of heat. Add to the weight and bulk the heat insulation. Thin aluminum will melt or fracture from the temperature difference if there in no insulation.

 

Your hull looks like it may have been well built, but I hope that your steam engine is very well balanced, because that thin aluminium hull will reverberate and may become annoying with vibrations at 5 rotations per second, 300 rpm, which may even cause harmonic induced stress fractures in the hull, or rattle your rivets. The engine mounting will need to be damped to minimise vibration transfer to the hull. I think a wood hull would be preferable. Lagging on pipes etc. will absorb rain if exposed, adding to weight. Will you cover the engine with a roof or housing ? That will add weight, as well as your water tank and coal box. Your engine's pressure gauge looks almost maxed out; maybe fit one that reads higher pressures and a wider range, for better temp observation / control, and a bigger safety margin for the gauge itself. All that smoke and steam and heat will be stifling in that small boat. Looks like fun though. Have you pressure tested it and been checked / certified by an engineer ? Several years ago a man here died when a cross threaded plug blew out, and shot him dead.

 

The boiler is well and good, 2x hydrostatic tested and all the proper things. I am an engineer myself and am very familiar with the relevant ASME calculations. The pressure gauge was far from maxed out, at 80 out of 160psi. You may have been looking at the stack temperature gauge, which needs to be replaced anyways after being overheated on a different project so accuracy is questionable at best. It was good enough at the time to get an idea of how well the fire was burning though.

The boiler itself is a self contained assembly that can easily bolt and unbolt, and weighs maybe 40 pounds, with the engine somewhere around 10 pounds. So the whole assembly will be fairly easy to remove and store indoors.

The comment about vibrations is something to think about though, as there are no balancing counterweights on the crankshaft, and the engine shook a lot when I managed to get it to 500rpm. I'll have to keep this in mind when mounting it.


I did get the inside painted this weekend. I got some quick dry enamel paint on marketplace. I've never used enamel paint before and it's a world apart from latex. It was a bit of a pain to work with, and I had to throw out the roller and brushes I used, but it feels much more indestructible than latex.


I did spot a problem relating to the propeller though. There's a big triangular reinforcement right in the middle of the transom, right where the shaft would go. So I'll have to think about this as I work on the wood.

 

Looking good in new paint. Since you're probably not mounting an OB motor anymore, you can do away with the central transom gusset, and reinforce the area again after your prop shaft and rudder are organised. Your gunnels may be smoother if you join the lengths and cut out the knots using scarf joints, and epoxy, to make continuous lengths from bow to transom, inside and outside, bending to continuous curves. If you don't have a rudder already organised, a small sailing dinghy rudder and tiller, with its gudgeons mounted on stern pintles may be a quick easy solution. Keep posting your progress and trials, it's an interesting project.

 

Yeah I don't like how that first try turned out. I'm gonna take them off and redo it in nicer wood with routed edges and seal or stain them before installing. I've got some nice 14ft or so boards I could cut down to make continuous (or at least almost) gunnels.

I didn't think about the possibility of removing that gusset. That will have to be later in the project, after I get it in the water with a regular outboard first just to test it. I have a power hand planer that I made a rudder with last year, so that should be fairly straightforward when I get to that point.

 

Honestly, I think the boiler is going to be your issue. Yes, I know that Michigan has a "hobby" exemption ( see SKILLED TRADES REGULATION ACT, Act 407 of 2016, section 339.5915 Article inapplicable to certain boilers, paragraph (f) Miniature steam or marine engines used as a hobby.) but paragraph (a) of that same section says it does not apply to boilers under "federal control".... and per the United States Code, it is under "federal control".... I think "miniature" is going to be gray area here

The law per Title 46 USC, subtitle II, part B, chapter 33

and the regulations
CFR Title 46, PART 58—MAIN AND AUXILIARY MACHINERY AND RELATED SYSTEMS, Subpart 58.03—Incorporation of Standards

Since 150 psi can throw a 5 lb part pretty far, and you seem to be able to do the stress calculations, as a PE I have done my due diligence. Be careful out there.

Edit to add;
There are a lot of other things in the USC and CFR, and here is a handy USCG guide.
https://www.uscgboating.org/images/514.PDF

 

What are the dimensions of the engine, including guards to keep people from getting burnt? Also, what is the CG and weight of the engine?

 

I'm really not here to answer endless confrontational questions about my boiler and it's safety until everyone and their grandma has been satisfied by my level of expertise, even if they've never touched a steam engine in person before. I already went through all that on actual steam engine forums, and I'm here for the boat aspect. I'm not the one letting teenagers throw around tanks of highly flammable liquid that floats on water, and bubbling toxic exhaust fumes directly into poor Nemo's breathing fluid.

The boiler itself is under 50 pounds and has about a 1ftx1ft square footprint. It's designed to be easily bolted and unbolted, so I can store it in the barn and use it for multiple applications. The engine is under 20 pounds and a bit smaller footprint.

On that note, I got the outside painted down below the waterline, and it's ready for wood. I took off those two gunnels and will redo them. Should I just stain the wood, or should I put polyurethane on it? I got triple coated deck screws for fastening, as I read that was recommended for aluminum boats in fresh water over galvanized.

Also, I stuck the propeller on my cordless drill and did some playing around with it in the pool. It's got a lot of thrust while fully submerged, but I think I might have a hard time getting it fully underwater without building some sort of outboard or stern drive type mechanism. That wouldn't be too hard to build, but adding a bevel gear set or two and the associated bearings will rob a bit of power. I'll have to do more research on HPB drives. I'm also considering making two more blades and doing some testing with a 4 blade prop partially surfaced. It would be pretty cool to get a force gauge and a handheld tach to do some pool testing with the drill. I know static thrust doesn't always translate to being good at speed though.

 

The wood and the screws should be isolated from the Al by a generous coating of plastic, regardless of what you put on it. You can choose your favorite PU or PS from a tube, just make sure it's not a permanent adhesive. Wood treatment is your choice, oiled or varnished (and stained beforehand if you want a color change).

Putting a prop under the boat is simple, measure the required space, determine shaft angle and fabricate the P bracket and shaft gland out of Al. Then you fix them under the boat with Al rivets. If you didn't include a thrust bearing in the crankshaft design or if the angle is so severe that you decide to use an articulated joint in the propshaft, you also need a thrust block riveted to the boat.

Why you are messing with big diameter props is beyond me, just buy a plastic prop intended for a low power electric trolling motor.

 

Because steam engines are a perfect match for large diameter very high efficiency (i.e. >85%) props.

 

Rolphill,

The boat looks great.

Have you considered a surface drive style prop driven through the transom?

EDIT: Forgot you already had the prop made.
Can you add two more blades?

 

Hah, I was literally working on another set of blades today to upgrade to a four blade prop. I was considering trying surface piercing out first. If it doesn't work, I can keep the hole and make it a stern drive type thing. Someone else suggested making the transom connection a rotatable joint, so you can rotate the assembly up out of the water for launching and weed clearing.