578 TRANSACTIONS OF SECTION G. 
His main object, as set forth fifteen years ago, was ‘to increase the power 
obtainable by the expansion of the steam beyond the limits possible with 
reciprocating engines,’ and subsequent investigations led Mr. Parsons to 
the conclusion that it would be possible to secure an economy of 15 to 20 per 
cent. by using the combination system as compared with that obtainable 
with efficient types of reciprocating engines. Many alternative arrange- . 
ments have been designed for combining reciprocating engines with low- 
pressure turbines ; that now under trial associates twin-screw reciprocating 
engines, in which the expansion of the steam is carried down to a pressure 
of 9 to 10 lbs. per square inch when working at maximum power, and then 
completed to the condenser pressure in a turbine. ‘Triple screws are 
employed, the central screw—driven by the turbine—running at a higher 
rate of revolution than the side screws, which are driven by the reciprocating 
engines. The Laurentic has been but a short time on service, and few 
particulars are available of her performances as compared with those of her 
sister ship, fitted with reciprocating engines. It has, however, been reported 
that the results have proved so satisfactory that the combination system will 
probably be adopted in the two large White Star steamers of 15,000 tons 
now building at Belfast. This favourable view is fully confirmed by the 
performances of the Otaki, built by Messrs. Denny, of Dumbarton, for the 
New Zealand Shipping Company, and completed last year. That firm, as 
is well known, have taken a leading part in the application of the Parsons 
type of steam turbine to the propulsion of mercantile and passenger 
steamers, and they possess exceptional experience as well as special facilities 
for the analysis of the results of trials of steamships, having been the first 
private firm to establish an experimental tank for testing models of ships 
and propellers on the model of that designed by Mr. W. Froude and adopted 
by the Admiralty. Messrs. Denny have generously placed at the disposal 
of their fellow-shipbuilders the principal results obtained on the official 
trials and earliest voyages of the Otaki, and have compared them with 
similar results obtained in sister ships fitted with reciprocating engines.* 
The Otaki is the first completed ship fitted with the combination system 
and subjected to trial on service, and as the successful application of that 
system to cargo steamers and steamers of the intermediate type would result 
in a considerable economy in the cost of oversea transport, it may be of 
interest to give some details of her recorded performance. She is 465 feet 
long, about 60 feet broad, and of 7,420 tons (gross). Her dead-weight 
capability is about 9,900 tons on a draught of 27 feet 6 inches, and the 
corresponding displacement (total weight) is 16,500 tons. The vessel was 
designed for a continuous sea-speed of 12 knots when fully laden, and the 
contract provided for a trial speed of 14 knots with 5,000 tons of dead-weight 
on board. The trials were accordingly made at a displacement of about 
11,700 tons. Her installation of boilers is identical with that of her sister 
ship, the reciprocating-engined twin-screw steamer Orari, which is 4 feet. 
6 inches shorter than the Otaki, but generally of the same form. On the 
measured mile the Otakz obtained a speed of 15 ‘knots, while the Orari 
reached 14°6 knots. In order to drive the Orari at 15 knots about 12 per 
cent. more horse-power would have been required, and this is a practical 
measure of the superiority of the combination system over the reciprocating 
twin-screw arrangement in the Orari. The total water consumption per 
hour of the Otaki at 15 knots was 6 per cent. less than that of the Orari at 
14:6 knots. If the Otakz also ran at 14°6 knots, the water consumption 
would have been 17 per cent. less than that of the Orari at the same speed. 
On the voyage from Liverpool to New Zealand the Otaki averaged about 
11 knots, which would have required on the measured mile only about 40 per 
1 See a paper by Engineer Commander Wisnom, R.N., in the Proceedings of the 
Institution of Engineers and Shipbuilders in Scotland for 1909, 
