Engine/Boiler Recommendation

A special section just for steam engines and boilers, as without these you may as well fit a sail.
JonRiley56
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Re: Engine/Boiler Recommendation

Post by JonRiley56 » Sun Oct 16, 2011 12:01 am

Hi Fred,

Thanks for the link. I will check it out. I had pretty much decided to go with your bilge keel idea until I got to thinking about how I am going to protect 20 ft or so of copper pipe along the hull. Now I am wondering whether I should go ahead and put in a regular keel with an aperture for the prop. It will certainly be more work than the bilge keel idea.

Any thoughts ?

jon
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barts
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Re: Engine/Boiler Recommendation

Post by barts » Sun Oct 16, 2011 12:39 am

To protect the pipe, you can just make it heavier, or lay it close to the hull. Any thing that will hurt the pipe (aside from perhaps knocks getting on and off the trailer) will destroy a spinning prop, so this is much less of an issue than one might think. I find a set of guides that insure that the boat sits down level on the trailer helps a lot with preventing difficulties at the boat ramp, and forestalling possible damage to the boat; here's a shot of the Otter after recovery at B & W last month. One can clearly see the black padded guides that help Otter settle down on her trailer. Recovery used to involve several tries until I fitted these guides; after that it's completely routine as long as the water is calm.

- Bart
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JonRiley56
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Re: Engine/Boiler Recommendation

Post by JonRiley56 » Mon Oct 17, 2011 12:22 am

Neat looking Boat !!

If I may be going to a larger engine in the future should I be thinking about building a boiler that is a little over sized for 5 hp ? Boilers are a pretty big ticket item.

Also, on a separate topic. How much water would I go throug an hour with a 30 sft boiler and a 5 hp engine ? I was drifting across some web postings and ran into some conversation about the potential issue of lubricating oil from the exhausted steam getting through to the feed pumps and boiler and causing issues......

If I only use 5 gallons an hour or so I could carry 20 gallons of DI water in an onboard tank........

jon
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fredrosse
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Re: Engine/Boiler Recommendation

Post by fredrosse » Mon Oct 17, 2011 1:59 am

5 Gallons per hour is about 42 pounds per hour (PPH), and for the launch engines in the 2-8 horsepower range, at least this amount of steam is required for each horsepower output. Some engines do better, some worse, but making 5 HP will definately require in the vicinity of about 200 - 250 PPH, a tall order for a 30 square foot boiler. A 30 square foot boiler can make about 180 PPH, probably more if forced considerably, but that would make for difficult cruising on the boat.

With about 150 PPH steam generation, a 3 horsepower engine can run comfortably, and will be capable of pushing a boat at hull speed with a proper propeller (having low speed & big diameter) up to about three tons total displacement. Most steam launches have considerably less than this displacement.

Hull speed is in the vicinity of 1.34 multiplied by the square root of the hull waterline length. For a hull with 25 feet waterline length, that computes to 6.7 knots, or 7.7 MPH.

Look under the thread "Steam Engine Fuel Efficiency" for more details.
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barts
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Re: Engine/Boiler Recommendation

Post by barts » Mon Oct 17, 2011 2:41 am

I agree with fredrosse; you really want to stick to the 5 gph/hp rule.

Note that the big issue w/ oil in the water is coating the tubes at the water line; this causes hot spots to develop, which can be a problem particularly with copper tubes. Since you're near salt water, you really want to run condensing. It isn't practical to carry enough water to run non-condensing for any length of time. I filter the hot well condensate, but I know it isn't perfect. so I also use TSP in the boiler to break up the oil, and have designed the boiler & gauge glass so that the tubes are completely covered at all times. This keeps the top of the water surface, and thus any oil, only against the inside of the drum which is very unlikely to have problems as a result.

- Bart
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