Those strange looking steam props

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Anne from Little Britan
Anne from Little Britan
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Joined: Tue Nov 17, 2009 11:17 pm
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Location: Roseville, MN
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Those strange looking steam props

Post by csonics » Wed Nov 18, 2009 5:12 pm

Posted on behalf of Doug B:

Doug B
Just Starting Out


Joined: 09 Apr 2008
Posts: 8
Location: Issaquah WA , USA
Posted: Wed Dec 03, 2008 6:42 pm Post subject: Those strange looking steam props
I need a little help here.

I'm considering modifying my three blade bronze prop to increase the steam engine RPM in my 19' fantail boat. Since I obtained this prop for free and probably will melt it down for another casing later, I think that I'll do a little experimenting with it first.

My 2.5" X 3.75" X 2" compound is running at 183 rpm at 140 psi now (that's 4.4 mph with one person on board). I'd like to run her up to at least 275 to 325. My boiler has enough steam to do this.

The prop is a Petersen 17" (diameter) X 25" (pitch) wheel. The blade area is pretty big. I think that the prop came off a troller of some kind. It probably transmitted well over a 100 hp.

I've seen several steam boats, mostly in pictures, with three or four long thin blades. I'm considering trimming up the edges of my prop, a little at a time, rebalancing it and seeing what that does to my rpm and water speed.

But I'd like to hear from some of you regarding your exerience with prop work first. Also I need to find some pictures of these long thin steamboat props.

Does anyone care to comment out there? I'm open to any and all ideas from other steamers.

Thanks,

Doug in Issaquah WA (USA)
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Maltelec
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Joined: 23 Sep 2007
Posts: 156
Location: Cumbria, UK
Posted: Thu Dec 04, 2008 12:50 pm Post subject:
I know when we measured the prop speed compared to the boat speed we were getting about 12% prop slip at most speeds.

Our prop is one of them big bladed things which most boats seem to have, I can't remember the pitch now but its 16" and I would guess at around 14" pitch as they are usually 1:1 or there abouts with steamboats.

The main thing to calculate is the speed of the boat you want, guess the prop slip (I would use 12% as a starting point as thats what we measured), and the speed you want for the engine. Then you should be able to calculate the pitch of propeller required and use it as a starting point.
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Froya66
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Joined: 12 Oct 2008
Posts: 9
Location: Esbjerg, Denmark
Posted: Sat Dec 06, 2008 4:04 am Post subject: Re: Those strange looking steam props
Hi Doug

I can give you a few numbers from a test I made this sommer.

My boat is 4 m long by 1.2 m wide. It has a calculated hull speed of 4.3 knots.

My propeller has a diameter of 270 mm and a pitch of 310 mm. I believe the DAR is approx 35 %.

At 2.9 knots the prop speed is 374 rpm giving a calculated slip of 23 %.

At 4.2 knots the prop speed is 623 rpm giving a slip of 33 %

If you have acces to older isues of the Funnel, you may find a test run of a number of boats a few years ago. I think also the slip was reported.

Recently there have been a number of stern and propeller fotos and I also remember an article about the consequence when trimming the propeller.

If you have no acces to the funnel, I might be able to find the stuf for you if you like.

By the way - when you say mph, do you then meen nautic miles?

Best Regards
Jørgen Hansen
Boat Frøya in Denmark
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