Wally and his friend, Arthur Knight, enjoy taking their steam-boats on camping trips in central Tasmania. There is plenty ofdriftwood and pure water and many isolated places to exploreand camp, indeed an ideal environment for a steamboat.Photo from the collection of Wally Mounster.

-plagiarize a design developed by Scott andNewcombe who built steam cars in the1930s. This consists of' a series of coilswound on a conical former as shown inFigure 1, and conforms to all the re-quirements set out above.

The conventional wisdom says thatstainless steels should not be used forboilers. My experience with the Stanleywas that each time I blew down, vastquantities of rust came out. Besides thedamage to the engine caused by the rust inthe steam, I was concerned at the thinningof the tube so I decided to investigate theuse of stainless steel.

One of the disadvantages claimed forstainless steel is that it has a relatively lowcoefficient of heat conduction. My calcula-tions showed that the heat drop in themetal tube wall was negligible comparedwith the heat drops at the gas-metal andliquid-metal interfaces, so stainless steelwas at no real disadvantage. There is also apossible problem with stress corrosioncaused by chlorides in the water. By usingthe good quality water from our local cityof Hobart, no problems of this nature havebeen experienced over six years of opera-tion. I purchased type 304 stainless steeltube, seam welded and annealed. The onlyleak I have experienced was a hair crackwhich developed after the boiler had beenoverheated; it was repaired by oxy-welding.

I decided to size the boiler generously tohelp with the pressure control problemsdescribed above. It consists of 250 feet oftube whose diameter varies from 5/8"