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16. TAE MARINE REVIEW material for baffling is eliminated and a very good econ- omical performance is promised. The most feasible arrangement in the space slicwed will be twelve boilers in three water-tight compartments. The grate surface as designed will be about 680 sq. ft. calling for about 25 I. H. P. per square foot of grate. The heating surface to be of a ratio a about 50. At full speed the boilers will consume about 300 tons of coal per day. BOILER ROOM AUXILIARIES. The boiler room auxiliaries will consist of blowers to be operated either by steam turbines or reciprocating engines. As the full power of these vessels will depend upon the proper functioning of the blowers, special precautions are taken to secure their reliability. They are to be placed in ample space on the deck immediately above the boilers where every facility for overhaul and operation may be pos- sible. Each boiler room will have a bilge pump for operating ash ejectors and for drainage and fire purposes. In these vessels which are intended to run under forced draft for long periods ash ejectors are a necessity. Each boiler room will also have a feed pump which will have 110° séa connection whatever to be used as an emergency feed pump, and for fill- ing and emptying boilers. By leaving off all salt water connections from the feed pumps the danger of getting salt water into boilers is reduced. The boilers are espe- cially designed to be accessible in every way for cleaning, operation and overhaul. : ' The weight of boilers for 16,000 I. H. P. is estimated at 200 tons wet (this does not include uptakes). Notwith- standing this light weight it is thought that these boilers will be as economical as any other type owing to the use of short grate, large ratio of heating surface and superior baffling arrangements. Owing to the fact that all parts are accessible and arranged so as to be in a position least favorable to deterioration, fairly long life for these boilers is assured. AUXILIARIES IN ENGINE ROOM. In selecting and providing for the auxiliaries for the scout vessels, special consideration must be given that these in' their characteristics do not nullify or detract from the effi- ciency of the main engines and the boilers, and that they are of such a type as not to interfere with necessary character- istics of the vessel as a whole. This is a somewhat complex problem and must be looked at from all sides from the standpoint of convenience of con- struction and installation, as well as from the requirements of convenience in operation and care. : The. auxiliaries may be classified into two divisions. (A) Those essential to the operation of the engines. (B) Those not essential to operation of engines. The design of the first class should have the paramount consideration. They are condenser, air and circulating pumps and feed pump. _ The condenser, air and circulating pumps are required for condensing the steam and securing the vacuum. In past torpedo boat practice too little attention has been given to securing thoroughly efficient apparatus of this kind. _The trials of most torpedo boats and torpedo boat destroy- ers give us a record of vacuum varying between 20 in. and 22 in. By careful design it is possible to obtain a vacuum of 28 in., the difference in the economical performance is one of great magnitude. If turbines are contemplated the import- ance of having a good vacuum is even greater than with reciprocating engines. For these reasons attached air pumps and Scoop con- densers are not contemplated. The saving of weight ob- tained resorting to these devices does not compensate for the decrease in efficiency and economy. The question of wet vacuum and dry' vacuum also ap- pears. Wet vacuum apparatus is the only one ordinarily in- stalled in marine work. The air pump being a reciprocat+ ing pump pumping the condensed water and vapor from: the bottom of condenser. In the dry vacuum apparatus the water and vapor are sepa- rated--the water is drawn off with an ordinary hot well pump and the vapor and air by the dry vacuum pump which is a high speed fly wheel pump. The dry vacuum apparatus "requires more space and adds one more auxiliary, but if such a system can produce a vacuum of 27% in. with 1 sq." foot of cooling surface per 16 lbs. of water condensed per hour, and the circulating water at 7o° Fahr., its value is probably enough to authorize its installation. In the turbine arrangement there is perhaps a greater possibility of giving the needed room, and in such ships the dry vacuum condensing apparatus may be installed with advantage. The type of circulating pump will be of involute centrifugal type. Its drive brings up the question of turbine versus reciprocating compound engines. Either is quite satis- factory when a good design is used, andthe difference in efficiency or weight one way or the other is hardly a ques- tion of importance. The high speed - centrifugal pump should be favorably. considered owing to reduction in size and weight over those of large diameter and low number of revolutions. Reliability is with the feed pump the prime consideration; weight and space must be sacrificed to secure it. The mar- 'gin of capacity, if a thoroughly reliable pump, can be some- what cut down from general naval practice. On the pres- ent design it is considered that 1.8 full boiler capacity at 100 ft. piston speed will provide a sufficient margin for the main feed pumps. AUXILIARIES NOT ESSENTIAL TO WORKING OF ENGINE. Feed heaters, though not absolutely essential, must: be fitted to secure the great gain in economy as well as -to les- sen wear and tear on boilers. Heaters on discharge side of main feed pump owing to their good efficiency will be used. An evaporating plant: sufficient to maintain the supply of extra feed at full power will be provided and reserve tanks for carrying an additional supply will also be fitted. Fire and bilge pumps are to be located as usual one in each engine and boiler compartment. The pumps in __ boiler compartments to be fitted for operating the ash ejectors and for extinguishing fires on grates. An ice machine and small refrigerating room are to oe supplied. This should be considered as a necessity and not as a luxury. A dynamo plant for lighting and operating _ electrical auxiliaries, such as ventilating blowers and work shop motors will be installed. Boat hoisting winches to be operated: by electricity. Steam steering and steam windlass engines will be fitted as usual practice in marine work. Owing to the fact that each boiler and each engine room is isolated, and as no transverse bulkheads are cut, special provision must be made for signaling orders from one point to another. ECONOMY. Considerations for economy for coal consumption in the design of a scout ship are of paramount importance, and in the lack of appreciation of this fact in U. S. torpedo design lies one great reason for the inability of many of our tor- pedo boats to obtain their original designed speed even for a short spurt over the measured mile. Probably the most successful torpedo boat builder in the world is Normand, and in his designs economy is thoroughly considered. The limit of the scout's usefulness is her endurance. This is directly dependent upon her economical performance,