The Steamboating Forum

My Semple 40 foot VFT boiler has a couple flue leaks. With the flues welded in, I'm looking at a major effort to replace all 72 1 inch flues, so am looking at possibly building a replacement from scratch.

The boiler supplies plenty of steam for the Semple 34 single in our 20 foot fiberglas boat, but I'm wondering about actual heating surface of this boiler. With water level at 1/2 glass, about 8 or 9 inches of flues are exposed inside the boiler leaving only about 2/3 of the total flues in boiling water.

In finding a replacement, is it reasonable to assume a 25+/- foot boiler would produce the same amount of steam as my current boiler based on those exposed flues, which in theory are not producing any steam? This question based on the concept that a replacement boiler would have all flues entirely submerged in the boiling water.

My wife and I truly like the look of the vertical boiler in our boat. Hence we are tearing ourselves away from using the Roberts type water tube in our garage. Thank you for not commenting on my mental abilities in this case.

Bruce Jahn

The tube surface above the water level does indeed participate in the boiling process. As water boils in the submerged tube areas of the boiler, internal splashing wets much of the tube surface above the apparent water line, and these surfaces serve to evaporate more water. Usually some portion (the upper elevation) of these tubes are exposed to dry steam, and in this case they superheat the steam somewhat.

Depending on the condition of your boiler shell/furnace, re-tubing may be considered. Cutters are available to machine out the welded tube attachments, leaving the tube holes virtually intact. This is a routine process for boiler repair shops.

fredrosse wrote:The tube surface above the water level does indeed participate in the boiling process. As water boils in the submerged tube areas of the boiler, internal splashing wets much of the tube surface above the apparent water line, and these surfaces serve to evaporate more water. Usually some portion (the upper elevation) of these tubes are exposed to dry steam, and in this case they superheat the steam somewhat.

Depending on the condition of your boiler shell/furnace, re-tubing may be considered. Cutters are available to machine out the welded tube attachments, leaving the tube holes virtually intact. This is a routine process for boiler repair shops.

And there's a code (or not, as you desire) boiler repair shop down in the Los Angeles area that could do the job. Check out Boschan Boiler & Restorations, 737 East 223rd Street, Carson, California 90745, 310-518-9977. No website now, but I've talked to Paul - he's built and repaired boilers from garden railroads to full size locomotives. Has done work for the Disney people.