Triple Expansion Engine - Elliott Bay

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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87gn@tahoe

Re: Triple Expansion Engine - Elliott Bay

Post by 87gn@tahoe » Sat Dec 05, 2009 1:47 pm

outstanding job!
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Re: Triple Expansion Engine - Elliott Bay

Post by mcandrew1894 » Sat Dec 05, 2009 1:47 pm

Excellent! I had great fun running mine on the brake, and I am sure you did to.

She looks wonderful!

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Re: Triple Expansion Engine - Elliott Bay

Post by Akitene » Sat Dec 05, 2009 1:48 pm

Good evening,

That's a great job, indeed!

I'm very impressed by the calculated 6.4 SHP because there's no condenser fitted to the engine. In this configuration, the triple engine is in fact almost like a twin cylinder compound engine. Due to the lack of pressure drop, the LP piston is merely travelling thanks to the global momentum of the crankshaft.

With a decent condenser, the LP engine should give a few more horsepowers to the whole engine, say 9 HP or even more. How many HP is this triple engine rated?

Anyway, you've built a splendid engine.

Have fun and keep us posted.
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Re: Triple Expansion Engine - Elliott Bay

Post by Edward » Sat Dec 05, 2009 1:48 pm

Dear Akitene ,

Your observations are correct concerning the lack of vacuum on the LP exhaust since no condenser or air pump has yet been fitted . In fact it was in some ways even worse as the LP cylinder drain was partly open and the steam supply was through a 6' uninsulated steel pipe with only 150psi at the boiler ! So we are not a little pleased with the result so far .
Ken Hall has a similar engine in his boat Oesa based in British Columbia as has Peter Cowie in Witch of Endor in Australia . Both run at 185 psi and at 375 rpm Ken reckons he is getting about 9 hp , Peter thinks he is getting about the same though I don't know if they have tested their engines on brakes .
When fitted with an insulated steam pipe , condenser and air pump and running at the boilers full pressure of 200 psi this engine could well be producing something like 10 hp .
It is a real credit to SteamboatJacks' engineering and machining skills .

Yours etc Edward
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Re: Triple Expansion Engine - Elliott Bay

Post by Akitene » Sat Dec 05, 2009 1:49 pm

Good morning Maltelec,

I'm not at all surprised by the overall expected power gain when insulated pipes and condenser + pumps system are used.

What kind of air pump do you plan to use? Are you planning to use a keel condenser or a conventional one (with fresh water circulating within pipes enclosed in a vessel)?

Regards,

Akitene
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Re: Triple Expansion Engine - Elliott Bay

Post by Edward » Sat Dec 05, 2009 1:49 pm

Dear Akitene ,

The air pump has a 3 1/4" bore and 2 1/4" stroke , it will fit onto the unpainted vertical plate on the front right of the bedplate (taking the HP cylinder as the front and looking from the front) . It is in the same casting as the feed pump and will be gear driven from the crankshaft with a 3:1 reduction .

I intend using a keel condenser . I prefer them over inboard condensers in launches for the following reasons :
1) They take up less room inside the hull leaving more space for
passengers etc .
2) They are simpler in that they don't need a separate pump to
circulate the cooling water .
3)They are usually lighter .
on the debit side they add to water resistance/drag and they are more vulnerable to accident damage , grounding etc .

Initially the condenser I intend to use has 4 x 3/4" tubes 45" long giving a surface area of 424 sq" . I am pretty certain this will be too small , but it came with the hull which already has the holes made for it .
I have made a pattern for the headers of a new condenser big enough to take 3 x 2" or 4 x 1" tubes which can be installed if/when the one I already have proves inadequate .
It will be interesting to see the comparison between the two .

All the best Edward
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Re: Triple Expansion Engine - Elliott Bay

Post by artemis » Sat Dec 05, 2009 1:49 pm

My experiences -and those of others - on condenser sizing indicate a rule of thumb: for keel condensers, 1/2 sq.ft. of cooling surface per engine horsepower; for inboard shell condensers, 1 sq.ft. of cooling surface per engine horsepower. So you may be a bit undersized. On the other hand, splitting the keel condenser into 4 tubes brings a greater volume into a close proximity to the cooling surface.
Ron Fossum
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Re: Triple Expansion Engine - Elliott Bay

Post by mcandrew1894 » Sat Dec 05, 2009 1:50 pm

Hi,

Thus far,,, 1/2 square foot per bhp on a keel condensor has been too small

Going to try my new one hopefully this Saturday at 1 square foot /BHP


Will let you know.

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Re: Triple Expansion Engine - Elliott Bay

Post by barts » Sat Dec 05, 2009 1:50 pm

Keep in mind that the water temp. affects the size of the condenser that is needed, as does the speed of the boat. In less sheltered areas here on the West Coast, the water temperatures are perhaps 55F.... but lakes and rivers are often much warmer, esp. on the surface in the summer, and hotwell temps climb accordingly.

Also, a feed water heater will help reduce the size of condenser that is needed.

Otter also likes to be moving; the keel condenser is too small when running full throttle tied to the dock (where I like to test new setups for a hour or so before casting off into the briny deeps Smile).

- Bart
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Bart Smaalders http://smaalders.net/barts Menlo Park, CA
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Re: Triple Expansion Engine - Elliott Bay

Post by artemis » Sat Dec 05, 2009 1:50 pm

When I moved my previous steamboat Artemis down from Puget Sound, Washington State, the keel condenser worked. Temperature of Puget Sound is 51F + or - 1F year around. On the Columbia River at Portland, Oregon I started having problems in August/September. Turned out the temperature of the river got up into the mid 70s in August/September (and down to 31/32F in the winter). Had to go to an inboard shell condenser to solve the problem
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