Stuarts don't give HP figures for the Twin or compound but suggest the Twin is suitable for Radio control and the Compound suitable for hulls of 1.4m to 1.8m long so unlikely to be usful for your needs. They quote the Cygnet as 1.5HP and the Swan as 3HP both on 100psi steam at 800rpm. Or the 5A at 0.63HP at 1000rpm on 60psi. These may give you something to go on and I assume that is power at the Crank.

Not sure if you know the sizes of Stuart engines but the 5A is a slightly over square 2.25" bore x 2" stroke so quite different you your hoped for output at 300rpm and obviously puts steam consumption up a lot if you are going to get your required figures..

Edited By JasonB on 28/05/2021 12:28:53

Ah… PLAN/33000 is indeed the theoretical power developed in the cylinder, but I take it you were careful to use the Mean Effective Pressure acting on the piston, not the boiler pressure? This is the mean of both admission-pressure and the expansion.

It is also lowered by multiplying the result above by a cautionary "Diagram Factor" that is highly variable, depending on clearance volume, compression (as the exhaust closes), superheat etc, but my references suggest around 0.8 a fair compromise.

Power at the crankshaft flange on a marine engine is usually also trimmed a bit by the condenser pumps, driven directly from the motion.

These may well explain why Stuart's figure is lower than you expected for the same engine.

If two people can padle a 4 meter long canoe to hull speed ,then 300 watts sounds more than sufficient.

The IMLEC results can point to cylinder size.

Lets have some engineering.

Two persons ,one on each bank of a canal with a Y wire and a fish Weigth and we are in buisness as naval architechts.

What is the maximum screw diameter You can accomodate?

Interesting project

From practical experience, I think that 2.6 HP would be way, more than required for a relatively slim hull:

A 2.2 HP petrol outboard would push our big, fat, inflatable dinghy with 3 people on board at more than walking pace on tick-over (this was an issue, as it didn't have a neutral!). At full throttle with one person on board, the thing could plane.

Rowing the same boat was a dismal experience – far less forward progress than a lesser effort in a wooden dinghy.

I think the ~0.5HP is much more likely. (Hull speed is ~5 kts, it becomes an exercise in rapidly diminishing returns if you are trying to exceed this.)

Looking at an old copy of the Steam boat Register (7th edition),

"LAUGHING WATER" LOA 19' 6", compound engine 2.5 + 4.5 x 2.5, boiler loco type 200 psi, 3 blade prop 15 x 25.

HEATHER LOA 17' Beam 2' 10" 3 cal radial 1.25 bore, boiler 3 drum water tubed, prop 3 blade 8 x 8

COUGH LOA 16', stuart turner No 1 (2×2), boiler flash steam 40psi, prop 3 blade 10×15

+1 for Niel's approach.

The problem with applying the 'scientific' approach directly is there are so many unknowns at the moment, for example:

• Operating conditions: traversing a canal with no head wind requires less power than steaming up a river, and much less than navigating a tideway in a storm!
• Weight of Passenger, Boiler, Engine, and Fuel
• Actual displacement
• Metacentre and stability considerations
• Duration (5 knots for how long?)
• Effect of hull form on propeller efficiency
• Propeller diameter and its design rpm.

Niel's suggests towing the canoe with ropes attached to weight scales. With a stopwatch, the actual power needed to pull a representatively loaded canoe at several speeds can be accurately determined with his technique. It gives the minimum Shaft Horse Power, or output watts, the motor must deliver for each speed. Minimum because the shaft bearings will add friction and the propeller won't be 100% efficient. Most of the output will be wasted if the propeller is run at the wrong speed, too near the surface, or is obstructed by the hull.

I couldn't find any power output data for Stuart motors on the web. Surprising, because I'd expect it to be well known after all these years. PLAN/33000 is far from accurate for real engines; so I'd hook up a Stuart to a dynamometer and measure it. Motors deliver maximum power at a particular RPM, which is likely to be closer to flat-out than chugging along. Measure the motors actual RPM and match the propeller to it with a gearbox as necessary. The size of the propeller is limited by the displacement of the canoe unless it's mounted outboard on a long boom and small propellers must be spun faster than large diameter propellers.

The power output of the motor is throttled by pipework size, insulation effectiveness, and boiler capacity. Bigger the better! For other than short runs, I suspect the size of the boiler and fuel supply that can be carried will limit what can be done.

How about a steam-electric hybrid? Lithium Ion batteries are relatively light and could be hidden away at the back and used to drive the propeller at adjustable speeds with an electric motor. However, on open display at the front a non-critical working steam engine, brass boiler, stack of coal and authentic smell. The steam engine efficiently drives a generator at constant speed to top up the batteries, while the electric motor sorts out propeller rpm. Range and speed is determined by whatever is stored in the batteries plus whatever can be generated by steam. If necessary, Lead Acid batteries could be used to ballast the canoe for stability.

Excellent project.

Dave

Hi Pete, I have a No 1 with reversing gear sitting here, I will try to weigh it tomorrow. Best wishes Noel.

While I would agree that the No 1 is about the right size, it has the single sided crosshead guide. This is not as robust as the bored crosshead design on the No. 5. Also the main and big end journals are bit on the small side for continuous work. This applies to the 5 to some extent too. I would suggest making a new crankshaft with the maximum diameter that the brasses can be made to accommodate.

The prop size is compromise, you want it large and slow turning for efficiency and small to permit low draft. Can't have your cake and eat it too!

Electric transmission makes sense when we have to match an engine to a highly variable load, but we already have a prop, which acts a bit like a torque converter, and a steam engine is also very flexible, so we don't need it.

John

Peter,

Not sure where you are in the world but 60Kg is too low for Europe. See https://www.worlddata.info/average-bodyheight.php

For the UK male=86.7 female=72.7

Adrian

I would have every confidence that a stuart No 1 would provide the power, like SOD My concern would be a boiler of the right size ! Though the traditional coal fire is nice an oil fired flash steam generator might be lighter and smaller. Building the engine with roller big end and mains may improve power and a torque tube shaft reduce weight. The issue of the prop, I would make (or buy) a unit that could have the blades pitch adjusted to find the best setting. Prop dia and pitch for any vessel is a black art,only truely resolved by experiment, calculations only put you in the ball park ! Keep us posted, and good luck. Noel.