The Steamboating Forum

Nice little launch at what seem to be a reasonable price. Not mine, just passing on the info.
http://www.ebay.com/itm/221689233091?_t ... EBIDX%3AIT

I notice that the top of the stack is cut in a zig zag pattern, for lack of a better word. I wonder if this has any particular effect on the smoke? Or is it just ornamental? I've seen photos of western river steamers with the stacks done this way.

" I wonder if this has any particular effect on the smoke? Or is it just ornamental?"

The "King's Crown" type stack outlet, just ornamental, traditional on western riverboats. I would like to find a nice brass ornamental piece to finish off my stack. Sometimes an ornamental brass piece from an umbrella holder has been used. I will keep looking.

fredrosse wrote:" I wonder if this has any particular effect on the smoke? Or is it just ornamental?"

The "King's Crown" type stack outlet, just ornamental, traditional on western riverboats. I would like to find a nice brass ornamental piece to finish off my stack. Sometimes an ornamental brass piece from an umbrella holder has been used. I will keep looking.

Or use an old brass spittoon or a "new" brass fruit, salad or whatever decorative bowl and have at it with the sheet metal cutters or small jig saw.

Lots of spun brass lamp parts will work for that.

-Ron

Hmm. Well, I'm in Baja until perhaps April or May and such cute things are a little thin on the ground down here. But thanks for the tips.

I was hoping that you would tell me that there was come magic that made the smoke not mess up the top bit of the stack or something like that.

I am more interested in the lower portion of the stack, I have never seen 2 small 3-4 inch outlets from the boiler leading into a 6 inch stack. can someone advise why this was done ? has anyone seen this before ?

If you look closely, the stack actually doesn't come down to the boiler casing, the elbows obviously bring the smoke/heat up either side of the steam drum and into the stack. Strange way to do it.
Daniel

I know thats what I was seeing an it is very different, have never seen that done before. I am interested in why they might have built it that way and how are they getting stability of the system as well.

Been thinking about this mystery, perhaps this is a reason:

This type of boiler often has a "steam dome", a piece of vertical pipe, somewhat smaller than the horizontal upper drum (steam/water drum), which is shown on some drawings as fitting within the base of the stack. The conventional arrangement, with or without the "steam dome", usually has the stack outlet directly above the center of the steam/water (upper) boiler drum.

With this conventional arrangement, hot flue gas from the fire must pass over the upper portions of the steam/water drum, as well as the steam dome, if fitted. These upper portions of the drum are not flooded with saturated water, only steam resides in the upper drum above the water level. Water level is usually maintained about half way up the drum, with only saturated steam above.

In terms of heat transfer, boiling water enjoys a very high heat transfer coefficient, thus boiler metal having hot flue gas on one side, and boiling water on the other side, is held very close to the water temperature. For example, with 1500F flue gas, and 350F boiling temperature, calculations will show the metal temperature below about 360F. Saturated/Superheated steam however has a very low heat transfer coefficient, and the metal temperature here is much closer to the average between the steam temperature and the flue gas temperature. For this example, about 900F metal temperature, which is why stainless steel (which can take the high metal temperatures) is often required for superheat coils, ordinary steel will burn out in some time.

With this type of boiler I have often wondered about the prudence of passing hot flue gas over boiler metal that is not in constant contact with liquid boiling water. If the gas has already cooled sufficiently, (giving up its heat energy to the boiler coils below) the boiler drum metal may not get overheated, if not, then there is a potentially dangerous condition. The ASME Boiler and Pressure Vessel Code prohibits ordinary steel exposure to 850F or above, and prohibits any copper based metal exceeding 406F.

Perhaps the boiler design we see here considers this potential problem, and insulation is applied to the upper part of the boiler's steam/water drum? This would avoid the overheat question, and as a result the stack arrangement would have to be something like the arrangement we see on this launch boiler.