MARINE MACHINERY

Shannon News, 19 February 1926, Page 2

MARINE MACHINERY

INCREASE Ox< MOTOR SHIPS. "AORANGI" AS AN EXAMPLE LONDON, December 11. , For the first time in history of the N mercantile marine the g-ross tonnage of motor ships being built definitely exceeds that of steamers actually under construction. The percentage of motor zonnage building in Great Britain, however, is only SS, as compared with 130 other countries. The development in marine machinery is the subject discussed by Mr. James Kichardson in the new- edition of "Brassey's Naval and Shipping Annual "The success oi .the quadruple screw . mail boat, the. Aorangi," says the writer of the chapter, "stimulated motor passenker liner construction, ,and the large ships Gripsholm and Asturias, shortly to go into commission, will mark the commencement of a new era. The engines have completed most successful bench trials of an exhaustive nature in the makers' works at Belfast, and are now being fitted on beard. The confidence of i the owners who. are adopting this form of propulsive machinery for their latest passenger liner is based on considerable experience of motor engines at sea. The substitution of the even torque of the perfectly-balanced notary prime mover of small mass, the steam turbine, by the unequal turning moment arising fiom the rapid reciprocation of enormous masses involving unbalanced couples of some moment as in these large Diesel engines ,is . mechanically a retrograde step justified only by the much more direct thermo-dynamical cycle involved in the latter ease. The combustion of th e fuel within the engine cylinders involves thermal changes in the entrapped air directly' convertible into vvork through the agency of the piston and crank. Is no compromise between these extremes possible? Geared Engines

"The internal combustion turbine is not yet developed, so that high-speed reciprocating oil engines geared to the propeller shaft either electrically, mechanically, or liydraulically, are suggested. The advantages of highspeed engines ar e being more generally realised in many quarters, and the tendency with internal combustion engine work generally is towards a higher speed or revolution, so reducing the weight, the cost, and the space occupied. The speed of the propeller is largely a fixed quantity, so that for marine work gearing is required. Except for special purpose ships, the first cost and th. 3 transmission are a serious drawback to this system. Very complete trials have been carried 'out in America to compare two tugs, qne with^' direct coupled oil engines, the other, having; electric transmission.

Substantial advantages in "economy and efficiency of operation were indicated .for the electric system; the motor on the propeller shaft being more readily adaptable than the- di-rect-coupled Diesel engine to the ■ varying conditions imposed as to whether the ship was running light, towing at full speed, or exerting the maximum pull or push at very small speed's. The extra cost of the electrical equipment would bo considerable, but whether the > advantages are. suffiient compensation even in this special case is not absolutely clear." A notable addition to 'motor liners will bo the Augustus, of 30,000 tons displacement. This vessel is being built by the Ansaldo Company in Genoa, to the order of the Navigazlone Generale Italiana, Genoa. The propelling 'machinery will comprise* four double-acting- two cycle engines of the M.A.N. type, each 4bf 0250 b.h.p continuous rating at 120 r.p.m.; 7000 b.h.p. at 125 revolutions per minute will be the trial performance. Each of the four main engines will have six cylinders of 27£in diameter by 47£in stroke. *