-- ------_._---- ._--------

The left-hand photo shows the boiler with its upper casing removed. Also show- opened or closed as required to regulate the draft. Just above the flywheel can being is part of the engine with the chain guards removed. Note that the engine is seen a wooden disk. This is a handwheel for small movements of the cam alonglocated off center beneath the driving position. This requires the use of a chain the camshaft to control cut-oft. The throttle handle is a similar wooden disk anddrive to the propeller shaft; however, it has several advantages. Firstly, it makes can be seen just below the pressure gauge: The photo on the right shows morethe controls handy to reach from the steering posliton. Secondly, the chain drive detail of the boiler. Note the large tube emerging from the center of the coil; thisenabled me to Change the speed ratio between the engine and prop. This saved is the outlet to the throttle. The small tube at the outside of the coil containsme buying a very big prop and allowed me to find the best speed for the 12" water. Normally the hole in the top of the coil is plugged, thereby torcinp hot fluediameter x 15" pitch prop. Thirdly, it leaves much more room in the cabin; this gas to pass between the tubes. Photos by Wally Mounster.keeps the wife happy' Note the fire door and the ashpan door. The ashpan door is

maximum at the superheater, reducing to1/2" and 3/8" in the evaporative areas and5/16" at the economiser. Surface area is 40square feet and the weight is approxi-mately 100 pounds.

Joints in the tube were kept to aminimum by purchasing each size in asingle length. Each joint was made with asleeve of larger tube and oxy-welded usingstainless steel filler rods.

Two people were required to coil thetube, one to rotate the former (like awinch) while the other guided the tube andheated it to just below red heat with theoxy. Each layer of tube was wound op-posite hand to the previous one; this re-duced the tendency for the outer layers tosink into the spacesbetween the coilsof thelayer below. However, spacers of 1/16"thick stainless steel were laid between the

layers to keep them apart.The boiler casing is made of mild steel

sheet, the upper part may easily be re-moved to gain accessto the tubes. A baffleis provided at the small (top) end of the coilto force the flue gases to pass through thetube nest to the outside of the casing fromwhere it passes up the stack. Only naturaldraft is used. The firebox is lined withFibrefax, a light-weight insulation madefrom kaolin (a type of white clay fromwhich porcelain is made) and which canwithstand temperatures up to 1200degreesC. Stainless steel sheet was placed insidethis after it was found to be subject todamage due to abrasion by the fuel.Fibrefax is also used to seal the fire-doorand the damper; this provides a positiveshutoff of air when it is required to stopsuddenly. The relatively shallow ash pan is

adequate for wood firing and the flimsyfire bars have stood up to six year's use.

The outside of the casing has beencovered with a layer of Fiberglass insula-tion and a second layer of galvanized steelto prevent burns to passengers. The boilerhas a nice traditional outside appearance.Using newspaper and kindling wood,steam can be raised in about four minutesfrom cold. It provides adequate steam todrive my 17' not-very-streamlined-hull atthe hull speed, burning approximately 10pounds of dry wood per hour.

The monotube boiler is ideal forgenerating steam at high temperatures andpressures, however there is no reason whyit should not be able to raise saturatedsteam for use in engines with slide valves.

In the following installment, the BoilerControl System will be discussed.

10 MODELTEC Magazine - May 1987