BOILERS FOR MARINE PURPOSES.

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the flues being divided with suitable water spaces, and are strength-ened at the top and bottom with conical tube stays, through whichthe steam rises and the circulation is effected. The water in theboiler is thus freely circulated, with the advantage of having a mode-

Fig. 29.—Overhead Flue Boilers. Longitudinal and Transverse Sections.aa, Furnaces. ß, Combustion chamber. c, Flues. dd, Circulating tubes. e, Uptake.

rate body of water, which, under certain circumstances, conduces torapid evaporation. There are side doors at the bottoms of the fluesfor the convenience of cleaning them out, which can be done insome instances while the vessel is under way. Another form of flue

Fig. 30.—Overhead Flue Boilers. Longitudinal and Transverse Sections.aa, Furnaces. b, Combustion chamber. c, Flues. d, Smoke-box. e, Uptake.

boiler in extensive use materially differs from the foregoing example.The flues are quite narrow, and are arranged overhead, similar totubulär arrangements. The flues are 3 feet 9 inches deep, 6 feet in