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-- ------_._---- ._-------- 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 be ing 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 along located 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 and drive 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 more the 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; this enabled 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 contains me 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 flue diameter 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 to 1/2" and 3/8" in the evaporative areas and 5/16" at the economiser. Surface area is 40 square feet and the weight is approxi- mately 100 pounds. Joints in the tube were kept to a minimum by purchasing each size in a single length. Each joint was made with a sleeve of larger tube and oxy-welded using stainless steel filler rods. Two people were required to coil the tube, one to rotate the former (like a winch) while the other guided the tube and heated it to just below red heat with the oxy. Each layer of tube was wound op- posite hand to the previous one; this re- duced the tendency for the outer layers to sink into the spaces between the coils of the layer 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 baffle is provided at the small (top) end of the coil to force the flue gases to pass through the tube nest to the outside of the casing from where it passes up the stack. Only natural draft is used. The firebox is lined with Fibrefax, a light-weight insulation made from kaolin (a type of white clay from which porcelain is made) and which can withstand temperatures up to 1200degrees C. Stainless steel sheet was placed inside this after it was found to be subject to damage due to abrasion by the fuel. Fibrefax is also used to seal the fire-door and the damper; this provides a positive shutoff of air when it is required to stop suddenly. The relatively shallow ash pan is adequate for wood firing and the flimsy fire bars have stood up to six year's use. The outside of the casing has been covered with a layer of Fiberglass insula- tion and a second layer of galvanized steel to prevent burns to passengers. The boiler has a nice traditional outside appearance. Using newspaper and kindling wood, steam can be raised in about four minutes from cold. It provides adequate steam to drive my 17' not-very-streamlined-hull at the hull speed, burning approximately 10 pounds of dry wood per hour. The monotube boiler is ideal for generating steam at high temperatures and pressures, however there is no reason why it should not be able to raise saturated steam for use in engines with slide valves. In the following installment, the Boiler Control System will be discussed. 10 MODELTEC Magazine - May 1987
