The Steamboating Forum

Does superheating make that much of an improvement to performance?

from what I have heard and read, it can make a big difference, but it also depends on whether you are using a single Engine or compound Engine,

a compound condensing Engine gets more profit by the superheating,


I have heard about a third less fuel consumption in a boat, but at my own boat where the difference is not so big, maybe 10-20%

Swedtug, what size is your boiler and how much length of superheater did you add ?

Stuart turner 6a with a John King boiler, I'm trying to decide to make the super heater or not.

Remember that with superheat comes the greater need for internal lubrication.

My boiler is a VFT with 150 tubes, 6.5 square meter heating Surface, It was a bit too small for the engine.
The superheater is abaut 9 feet 1 inch of industrial superheater pipes, which is localized under the tubes.
the heat is about 260 celcius or 500 f. The cylinder oil that I use can't take much more heat.

A moderate sized superheater can be advantageous as it ensures dry steam, I would be weary of anything of a capacity similar to that of a locomotive, I think it's probably more trouble than its worth. One important point there should be NO valve between the steam drum and the superheater. I sometimes see small boilers with such a valve and its wrong as it potentially allows the superheater to be isolated at both ends and therefore over pressured by heat. Large boilers do not have such a valve and they invariably have a second set of safety valves on the superheater outlet header set lower than the drum valves.
I personally don't think a second safety valve is required on small boat boilers, an alternative is to mount the (only) safety valve on the superheater outlet header, but with a modest size of superheater the drum valve should suffice.
Regards
Jack

Hi John- I run a superheater but just for the atomizer. It is a loop of stainless into the boiler and out again so it's only about 2 ft long. When burning wood it would be empty of water so I would assume that's why the builder went to Stainless other wise other materials might melt. Dunno but it works great though I did plumb a drain before it goes to the burner as there always is a little water in the pipe which puts out the wood fire when switching to oil. Embarassing when surrounded by people at the dock and one has to explain what just happened Mind you ,this has never happened to me but I've seen other people have this problem. OK OK maybe once or twice it happened to me Den

I have often wondered about how feasible it would be to fit a 'moderate sized' superheater to our boat, compound engine, coal fired vertical fire tube boiler, lubricator (separate) for the steam already in use.

Again, while ok for most work, the boiler is far from oversized, and for broader canal and certainly river work the above quoted 20-30% more poke would be very nice to have.

The issue I have is what happens if you stop, obviously you aim to plan ahead, but sometimes you just do have to stop suddenly with a full fire in. What happens to the superheater then? Does it not get bloody hot and start glowing a dull red in the flames?


Daniel

Yes I suspect that they will be glowing dull red sometimes, so it is probably important to exaggerate the pipe wall thickness .




The industrial tubes which I use contained nickel i think to increase the strength when heated

Johan