Propeller

[johnp]

What's a propeller with?

[Maltelec]

Hi John

You'll have to explain a little more as your question doesn't make any sense.

[johnp]

sorry, what's a propeller worth? (cost)

[fredrosse]

I buy bronze three two and three blade propellers frequently on e-bay, in the vivinity of 12 to 20 inch diameter , for about $25 - $50 USD. I only buy right hand, with pitch at least equal to diameter, in very good or new condition. This is bargian basement pricing, and you have to look for a relatively long time to find the one you want, but eventually it will show up. If you buy these at retail outlets, you will be paying in the vicinity of ten times these amounts.

Many marinas have a limited selection of nearly new propellers, as power boat owners are always trying a change in pitch to get the most performance from their boats. These slightly used propellers can be had for prices about half way between retail and e-bay bargians, however the majority have pitch to diameter ratios somewhat less than 1, which is not what we steamboaters usually want.

Example picture below is an 18 x 21 prop on e-bay now, but left handed.

[dhic001]

The trouble is that motor boat props aren't really suitable for steam, even though they are commonly used. The prop pictured above would be fine if you have heaps of horsepower and aren't worried about efficency, but that would be a rare boat. maybe you can buy a motor boat prop, set it up in the vice and attack it with the angle grinder and eventually end up with something decent, but I haven't tried it. Can't say i'd fancy trying to take 2/3rds the blade area off that prop!

The alternative is to make one. For a modern glued or firbeglass boat you can machine a hub in stainless and weld one up, or do it in steel and get it galvanised, or for very long term use, make a pattern and cast it up. At the bottom of this page http://www.steamlaunch.co.nz/Steamlaunch.html you'll see some patterns. In the end though a stainless unit was made up for the one boat that has run. It didn't look like a normal prop, being more like a component from a very large food blender. Zeltic's new prop is shown in the following picture, and is an enlarged version of the food blender unit, but 3 bladed and in steel.

it works fantastically well, and was easy to repitch when we started with too much 9as pictured. its now 24 by 47.

Daniel

[fredrosse]

I think we all agree that the typical motorboat prop is not as efficient as a slim "steam wheel", however the loss of efficiency is relatively minor, especially for a slow turning prop.

Cutting half of the blade area off a typical 3 blade prop, and properly fairing the edges will take considerable time, maybe 10 to 40 hours work, and that will maybe give a typical steam launch a small fraction of one MPH improvement. Making a built up propeller, or casting one, much more labor than that.

Of course, we all choose how to use our time, many people spend 5 hours every day looking at a television, and I think building things is better entertainment.

[S. Weaver]

I buy bronze three two and three blade propellers frequently on e-bay, in the vicinity of 12 to 20 inch diameter ...

So you're the one I'm frequently bidding against ... just kidding. At work we have this joke that we are all bidding against each other for the same gauges, valves, trinkets, etc.