Very very lightweight steamboat..Suitable engine?

[rogercrier]

We are talking 200lb displacement, 10 ft long with a good hull shape, and I am hoping to fit my Stuart D10 and push it to it's limit. I need a recommended prop pitch and diameter to start experimentation....I am trying to get info on the power capability of this tiny Stuart engine (3/4" bore and stroke double acting twin) and a suitable prop size to extract it's best performance, with the intention of sticking it in my boat, A picture and full details of which are in the link below.
http://gaboats.com/boats/whitehalljr.html

From figures found elsewhere, it stacks up like this (if you put your tongue in your cheek)

If a 1 1/2" Bore and stroke Stuart Turner Swan gives 3 hp , a Stuart D10 is 1/8th of that capacity so gives 1/8th of 3 or .375 HP
The hull speed is 4.1 knots and hull speed takes 1hp per ton. 200lbs is 1/11th of a ton so 1/11th of a hp should do it and the D10 has 3/8th's of a hp

The prop should be 8% of boat length, giving 9 1/2" dia and have a 10" pitch or greater.
Anyone who can make better educated guesses please reply, even if it is to tell me I need locking up!
If the Stuart fails to come up to snuff I will build a smaller version of Ray Hasbrouke's Number 8 engine, ending up with a 1" bore and stroke double acting 90 deg V twin, but hope not to have to, as I am sure the Stuart is man enough if it gets the right prop....

[Edward]

Hello Roger ,

Not sure that you need locking up , it should be a fun project , but I'm pretty sure that the Stuart D10 is nothing like powerful enough neither does it have robust enough bearings or crankshaft for what you envisage .
I don't know enough about the Hazebrouke engine to comment about it but as an alternative the Stuart No 1 would certainly be up to the job if the bearings and crosshead were constructed as robustly as space allows . The Stuart No 4 might also fit the bill (with the same proviso about bearings etc ,) the No 5 can certainly be robust enough but is probably more powerful than you need and with its boiler is likely to be too heavy .
Most of the Stuart engines are definitely models and were not designed for prolonged hard work but the No 1 has been used in several small boats and canoes , the No 5 is a fairly powerful engine and has been used quite a lot in boats of up to 18' .

Hope this is of some use .
Regards Edward .

[rogercrier]

Hi Edward,

I have just edited the original post and added some info found on here and other places, so have another read. I know that I am basically using an engine out of a big RC model boat, but look at the weight! It is way lighter than you guys are used to, due to the total lack of mahogany )

My biggest worry is if a red hot 7 ba nut vibrates off and lands on the hull, it will melt it's way straight through the Dacron covering!!!!

[fredrosse]

I have a Saito T2GR engine (0.79 inch bore & stroke, two cylinder, double acting) in a large radio controlled ship model, which weighs almost 100 pounds when ballasted to the waterline. Saito lists the power output as 0.1 HP at 3600 RPM, with 30 PSIG steam pressure (2 atmospheres gauge pressure).

This model engine is far more powerful than is needed for the boat, and the max RPM is about 1800. It is direct connected to a four inch diameter cast aluminum propeller. The prop looks like a ships propeller, but was originally a prop used to mix drywall compound, and I have no idea what the pitch is, however it is a good match to the Saito engine. I have had this model since 1987, and the engine has held up well,

The D10 should perform similarly, but the bearings will be overloaded if you push the steam pressure & RPM up to the point of getting 3/8 HP.

I would guess you can get a 6 x 6 prop up to 1000 RPM , giving you about 3.5 knots with 0.15 HP @ 50 – 75 PSIG steam pressure. That is probably pushing the D10 to the limit .

You can make a steam engine from a “weed eater” two stroke machine, and these have roller bearing crank mains and connecting rod bearings, much better for your intended service. But only single cylinder, single acting.

[rogercrier]

Thanks Fredrosse, that's usefull info! I may look at fitting ball races wherever I can in the D10, but if it wears out, then that's an excuse to make something else.

I have all of the Ray Hasbrouck plans, and his no 9 engine is a 3/4" x 3/4" twin oscillating engine that he said is capable of strong work and out performs the D10, is lighter, and is easier and quicker to machine. But for now I have a D10, so will have to make do!

[fredrosse]

Just an example, a double acting vertical engine I built from a Homelite 28cc (1-5/16 bore, 1-1/4 stroke) chain saw crankshaft, connecting rod and piston. The engine has needle bearing mains and roller bearing connecting rod big end bearing, the original piston is used as the crosshead. This engine was made with no castings required.

[fredrosse]

The steam coaster with Saito two cylinder engine. Next is Muskrat, a Wineglass Wherry, 12 foot long fiberglass boat with a Stuart No 1 engine. This boat, about twice the displacement you are contemplating, gets along very well with the Stuart No 1 engine.

[rogercrier]

They are nice boats, but a lick of paint wouldn't go amiss on the smaller one

I can see a "weed wacker" based steam engine in my future, so thanks for the info and design hints, although I will persevere with the D10 as it is already started.

I will report back when "sea trials" start in earnest!!

[fredrosse]

The steam coaster was caught in a fire years ago, and I had to repair the hull with fiberglass-epoxy, sanding and priming, etc. The little ship sat on the mantle for years. An established interior decorator was visiting, and when I mentioned I was about to paint the ship, she went ballistic, indicating that to paint such an antique and weathered finish would be a sin. So it stays as it is, perhaps an old tramp steamer that needs a paint job.

I built a small double acting vertical engine fron castings, similar to a Stuart V10, single cylinder. The build/machining process is described here: http://www.classicsteamengineering.com/ ... 677#msg677
Hope you might find some of this interesting.

[Mjolnir]

I think there is some kind of law against treating small steam engines so cruelly The maximum power for a steam engine is determined by how much load the bearings can stand and how fast you are prepared to let it rev. Higher pressure will give you more power at any given speed, letting it rev will give you more power at the higher speed, up to the point where the flow rate through the ports becomes a limit, more pressure will help to overcome that, but at some point the whole thing is going to disintegrate, either due to the inertia loads, or the steam loads, or both. Plus of course high RPM might get you a lot of power at the crankshaft, it is another thing again to get that power into the water via a propellor. If you check out the sort of thing that has been done with steam hydroplanes, you can get a couple of horsepower out of an engine that you can easily hold in the palm of one hand.

You might though be better to look at say the locomobile engine as a design. That is a reasonable size of engine, but extremely lightly built with high quality materials. The result is a powerful engine that does not need to run at high speeds. It would probably want scaling down to a suitable size, but would be a good way to go.

regards
John