. A manual of marine engineering: comprising the design, construction, and working of marine machinery. metimes, to minimisethe transverse size of the boiler-hatch, it is made of oval section. Thefunnels of men-of-war are often made of oval section for the same reason,but, instead of the section being an ellipse, as is generally the case in themercantile marine, it is like that of an oval boiler. The best height to lookwell is 5 to 7 diameters above the taffrail, the latter when there are highbridges or boats in wake of the funnel. For the same reason, the ring for 468 MANUAL OF MARINE ENGINEE
. A manual of marine engineering: comprising the design, construction, and working of marine machinery. metimes, to minimisethe transverse size of the boiler-hatch, it is made of oval section. Thefunnels of men-of-war are often made of oval section for the same reason,but, instead of the section being an ellipse, as is generally the case in themercantile marine, it is like that of an oval boiler. The best height to lookwell is 5 to 7 diameters above the taffrail, the latter when there are highbridges or boats in wake of the funnel. For the same reason, the ring for 468 MANUAL OF MARINE ENGINEERING. the shrouds should be -^ the diameter from the top. Funnels are made ofship quality plate, lap-jointed, or butt-jointed with single straps inside; thelatter costs more, but when so made is more durable. Another methodmuch in fashion at one time, and which presents a good appearance, is tomake the longitudinal joints with inside butt-straps, and the circumferentialwith a band of iron of a flattened U section (fig. 180). The funnel plates should, for strength, be thicker at the base than at the. Fig. 179.—Naval and Yacht Funnel Top. Fig. 180.—Ordinary Funnel, withHood, &c. top, but the top plates wear out faster than those at the bottom. Thefollowing may be taken as the approximate thickness of funnel plates :— Top plates = 0-1 inch -f 0-025 for each foot of diameter. Middle „ = 0-125 „ + 0-026 Bottom „ = 0-15 „ + 0-027 „ „ If the funnel is stiffened with angle or T bars (fig. 179), it may be made FURNACE FRONTS AND DOORS. -169 of somewhat thinner plates. The funnels of naval ships are, of course,made as light as possible, and the plates composing them are seldom morethan -^jj inch thick, and of steel. TABLE XLVII.—Pitch, &c., of Riveting for Funnels, Casings, &c. (Admiralty Work). Description. Thickness ofPlate. Uptakes, Funnels, Funnel casing. Deck casings, Cowls and trunks (exposed to /weather), - - - - \ Screens and ventilating trunks, - -j Inches. O
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