74

MODERN STEAM PRACTICE.

made with a flat ring and iron moulding. At the top horizontaljoint, or 27 feet from the bottom of the funnel, lugs are forged onthe ring, on which to fix links for the funnel shrouds, which aresecured below to the side of the ship.

Tliickness of Bottom Plates,. A inch.

Do. of Top Plates,. & ,,

Joint Straps,.4 2 * ts >>

Flat Rounded Moulding,. 3 inches.

The bottom of the funnel is fitted to a cast-iron ring secured to thetop of the steam-chest. Where four boilers are used this ring isdivided into four parts, with cross bars of cast-iron, cast in one piece,to which is fitted a damper for each boiler, having an uptake fromeach, independently of the others, that the draught of each boilermay be regulated separately. One of the cross bars is cast hollow,forming a pipe from the side to the centre of the ring, or centreof the funnel; this is termed the blow-pipe, and is fitted with aplug-valve in connection with the steam-room in the boiler. Theengineer by this means can urge on the fires by blowing the steamup the chimney, and thereby causing a partial displacement of theair, which is filled up by the atmospheric air rushing under the fire-bars and through the holes left in the furnace doors, providing thelarge supply of oxygen so necessary for combustion. With high-pressure engines the waste steam from the cylinders is blown upthe chimney in a manner similar to the blast-pipe of the locomotiveengine.

Funnels of large diameter are usually stayed internally withround bar iron, to prevent them from getting out of shape in theworkshop or on carriage to the ship. For ships of war the funnelis made telescopic, the top part sliding into the lower part. Theoutside part, or lower portion, is formed conical at top, with a cor-responding cone for the internal or top portion, fitted at the bottom.Thus, when the top part is hoisted up, the inside cone fits into theouter one, and the funnel is screwed hard up with set screws, swivel-ling in boxes recessed in the funnel. The points of the screws bearon an angle-iron, fitted round the outer portion. The top part haslikewise the shrouds for securing the funnel to the ship’s side. Themechanism for hoisting up the funnel is a worm-wheel and pinion,with the necessary barreis, chains, and guide blocks. This gearshould, when possible, be fastened down to the top of the boilers,or strongly bolted to the side plates of the bunkers, as the worm-