TABLE I.-WEIGHT AND SPACE OCCUPIED BY VARIOUS MAKES OF WATER-TUBE BOILERS No grates-oil burning. Weights are for boilers and fittings with water, and do not include up-takes and funnels. DREDGES FITTED WITH WATER-TUBE BOILERS P ERHAPS in no other industry is the underlying principle of commercial efficiency so slightly defined and unrecognizable as in the work of dredging. The number of hands required to operate the dredge is relatively small; and, unlike the power plant of a large mill or factory, when the plant shuts down few people are rendered idle. Delay results in no damage to the material and the work can be taken up again at leisure when repairs or overhauls are finished. It is not strange, therefore, that in the minds of many designers of dredging installations "first cost" assumes overwhelming consideration. With them it is not a question of how continuously the plant is to be kept in operation, but of how cheaply it can be built. Second-hand machinery is often used and there is no type of steam generator that cannot get a trial, provided it can be purchased for little money. And yet, on the other hand, in no other industry is the saying "Time is money" so forcibly true as it is in dredging. Particularly in the light of active competition in bidding for contracts, the operator who makes his plant pay the largest return on the investment is he who keeps his dredge ceaselessly at work at full capacity, days and nights, one hundred and sixtyeight hours a week. An inconspicuous lack in steaming ability, slightly fewer revolutions per minute and slightly fewer cubic yards per hour will, in the aggregate, mean the loss of many thousands of dollars; and a brief shut-down for renewal or repairs may offset many times over a very considerable difference in first cost. Ample steam capacity and economy of fuel are very vital features to be considered in the building of a dredge, and the value of a durable, dependable boiler that will keep things moving all the time at full power cannot properly be figured at so many cents per pound. To supply a suitable boiler for dredges, both stationary and those of the self-propelling, hopper type, a special class of Babcock & Wilcox boiler has been designed possessing features which specially commend it for this class of work. The illustrations show a sectional side view and a perspective view of such a boiler, from which it will be noted that, in its general characteristics, it is similar to the usual "Alert" design of Marine Boiler, that is the boiler is fired from the low end and there is the same system of baffling. The tubes, however, are all 4 inches in diameter No. 8 B. W. G. (0.165") thick and of much greater length. This is usually 12 feet but may be made 14 feet where special circumstances require it. It will be noted also that the usual water-boxes on the sides have been omitted and are replaced by brickwork. This boiler has the same large furnace, increasing in volume towards the bridgewall, and, like the Alert design, is equally adapted to burning coal or oil fuel. This boiler is of unusually robust construction and can, therefore, be depended upon for thorough reliability under the trying conditions which usually obtain upon dredges. As will be seen by the following illustrations and descriptions, boilers of this class have been extensively used and have given great satisfaction. |