Engine choice

[johnp]

Which would you buy? Taylor twin or A Beaver compound. Going in a 18' x 5' boat. Max propeller dia 15" both probably need the same work. One needs completing one needs cleaning up.

[Rainer]

Take the compound.
It consumes less steam and has enough power for your project. In my register there are 3 boats with the Bever engine. Have look here:
http://www.steamboating.de/steamboat/st ... p#Compound

This 3 boats are 16' 1" , 16' 8" and 18" long...

[DetroiTug]

One could write a book on this question, but I'll take the twin.

-Ron

[johnp]

Why the twin?

[TahoeSteam]

John,

I would have to agree with Ranier on the Beaver compound. 18' isn't a particularly large boat and the larger boiler and extra fuel needed to run a twin vs. a compound could take up quite a bit of space.

[johnp]

I thought the AVL was the same config as a 6a? I'm building a John King yarrow type boiler. Should have enough supply for either.

[TahoeSteam]

I thought the AVL was the same config as a 6a? I'm building a John King yarrow type boiler. Should have enough supply for either.

AVL dimensions are 2-5/8" + 4-1/2" x 4" I've seen this engine power a 25'x7' launch very easily.

Stuart 6A dimensions are 2-1/2" + 4" x 3"

Burleigh dimensions are 3" + 5" x 4" Not much bigger than the AVL and the overall size of the original design Burleigh isn't much larger than the AVL.

I'm sure the Yarrow boiler would be more than ample.

[DetroiTug]

Why the twin?

In my own personal experience I like the twins better in the engine sizes we use (2 - 4" bore and 2 - 4" stroke). Comparing engines by type and different boats I've ridden on, the twin seems a better all around performer. It does use more fuel, it does use more steam, but it also does more work in a wider range of conditions. My opinion is the Compound has more power at low RPM, but the RPM is limited. A twin or single simple can easily exceed that RPM and provide more power.

The twin is easier to operate, warming through is very simple. Start up procedure on my tug: Both steam chest drains are piped to one valve. At start up the main steam and throttle are opened and the stephenson link is put in the fore position. The chest drains are opened. As steam rises, it flows through the steam chests warming the engine. At about 10 psi the engine will begin to revolve at a very slow speed, as pressure comes up, start tapering the throttle back and cut in the hydro oiler, and it's ready to go. Forward and reverse are 100% reliable, even down to 10 psi. No vacuum pump is needed at all - which is a marginal negative to shaft horsepower. Everything that happens in a steam plant costs something.

A few things left out of the conversations in my reading on compounding cylinders is the back pressure imposed on the HP cylinder by the LP cylinder. Also to route exhaust steam from the HP to the LP involves many turns and some thermal losses. The many turns result in internal restrictions and limit the RPM and horsepower output at higher RPM's.

Virtually all steam locomotives were twin simples. The same for steam cars. Large ships did primarily use compounding engines and typically ran at very low RPM's.

Just my opinions on the comparison of the two - and probably wrong

-Ron

[farmerden]

Love my compound!! However they don't work much below 120 psi as the low pressure "goes along for the ride " due to low pressure. A twin uses more steam but should perform better at lower pressures. Any agreement or diagreement? I love controversy!! Den

[Lopez Mike]

I have been reading about compound engines for half a century. I have seen all sorts of data on large engines that support the thesis that compounding reduces steam consumption. I have not been able to find any tests of small compounds that agree or disagree with that idea. Lots of indicator cards but nothing that looks like a good comparison between simple and compounds of the same size and power.

My own very limited experience leads me to think that most of the time the low pressure cylinder is along for the ride. The ratio of cylinder volume to surface area in our small engines makes them work about as well as condensers as anything. I have a friend with a compound locomotive who has never seen any pressure in the receiver (the pipe from the high pressure cylinder to the low pressure cylinder) under even continuous high power running.

I love looking at small compounds but I can't say that they are any more efficient than a twin. I guess if you make long runs at higher throttle settings it might help to compound an engine. I think we loose more fuel from lack of good feed water heating and poor insulation of pipes AND the boiler than we might ever get from mechanical arrangements.

I do a lot of maneuvering in tight quarters. If I had a compound I would put a lot of effort into making sure that it was dead reliable reversing at light throttle openings.

Mike