The Steamboating Forum

"....So for example an 3 x 17 x 26 prop. would be adequate? Or would you recommend an 2 or 4 blade prop?"

Comparing the recommended prop, 18 inch diameter x 27.5 inch pitch at 300 RPM, vs your propeller with 3 blades x 17 inch dia. x 26 inch pitch, which is about 6% less pitch, this can be accommodated with about 6% higher shaft RPM, say 317 RPM No significant difference here.

As to the number of blades, this depends on the blade area required, and you would probably be OK with a typical motorboat propeller having 2 blades. A "steam wheel propeller", having 3 blades which are much thinner (less blade area and less blade thickness) than typical motorboat three blade propellers would be most ideal. The typical three blade propeller for motorboats has somewhat more blade area than you would need, however satisfactory operation with this type propeller is OK, just a bit less than ideal.

Note that a propeller of 17 or 18 inch diameter for motorboat service is typically OK for over 30 knots with several hundred horsepower IC engines. running at a couple thousand RPM. Therefore they are typically far more robust than necessary for our steam launches running at only a few horsepower.

How does one determine necessary blade area for a given displacement and desired speed?

I had good luck using the formulas in Dave Gerr's Propeller Handbook. That's where I arrived at the 22 sq. in blade area for Reciproca's 17"x26" prop.

YouTube of Reciproca in action.

And she is able to get out of her own way.

Thank you for the info Kelly.

I've watched the video of Reciproca many a time. She fairly scoots. What a beautiful launch and steam plant. You really did a wonderful job.

Note the similarity between the most efficient prop for a steamboat, and that for a human-powered boat:

http://recumbents.com/wisil/hpb/prop/default.htm

Some of the athletes are capable of outputs (for a short while) that exceed that of small steamboats.

- Bart

barts wrote: ↑Mon Feb 07, 2022 8:56 pm Note the similarity between the most efficient prop for a steamboat, and that for a human-powered boat:

http://recumbents.com/wisil/hpb/prop/default.htm

Some of the athletes are capable of outputs (for a short while) that exceed that of small steamboats.

That's a cool site, thanks for posting the link.

As speedy as Reciproca is, I must admit to losing a race to an oldster in a fine lined kayak. I'm not sure that he knew that I was even racing with him. How humiliating!

As speedy as Reciproca is, I must admit to losing a race to an oldster in a fine lined kayak. I'm not sure that he knew that I was even racing with him. How humiliating!

Some fifty years ago, my dad and I mounted a tiny, lightweight outboard (an 1.5 hp AquaBug iirc - hard to keep running well) on a 17' Klepper double kayak on a small overhung arm. That thing moved right along; the narrow hull sliced through the water with the two of us on board; if we'd had a prop w/ more pitch, I'm sure it would have gone faster. The engine was noisy and unpleasant, and died a few years later. Paddling was more fun if slower.

Anyone wanting a fast seaworthy steamboat that could be carried on top of a car would do well to consider a hull shaped like a Klepper Aerius. Dr. Hannes Lindemann crossed the Atlantic in one of these equipped w/ a sail. The hulls are not light (~75 lbs) as they fold up, but they're very burdensome - rated for 700+ lbs carrying capacity. A wooden kayak of that form (beam 34") would likely weigh less than the folding one... a HasBrouck engine would push one along easily at nearly 6 knots with a narrow bladed 'steamboat' propeller. The steam engine, fuel and boiler could be removed separately to make single handed launch and retrieval practical w/o a launch ramp.

Another someday project

- Bart