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276 ,times-the ahead full load torque- It - will be obvious,. therefore, that a tur- bine capable of developing 40 per cent of the full power ahead, actually has a starting and stopping torque 'greater than the full load torque ahead. The maximum torque which 'a reciprocating engine can develop is 'equal to the area of the pistons into 'the mean effective pressure with cut- 'off at full stroke. Therefore, the 'turbine can be brought to rest and reversed more rapidly than the recip- rocating engine. As the propeller 'speed in the geared turbine installa- tion is about. the sameras that which would" be used in a reciprocating en- gine vessel, the maneuvering qualities 'of a turbine with 40 to 45 per cent 'of the ahead power would be .some- what better than that of the recipro- cating engine. | Advocates' of the reciprocating en- gine may raise an objection at 'this-. point by calling attention to the fact that the energy stored in the turbine 'rotor and gear wheel exceeds that . 'stored -- in the reciprocating parts of an engine. fortunate _ that' the greater stopping 'torque of. the turbine is sufficient to. more than offset the greater stored energy. The turbine has further the ad- vantage that the torque at very low speeds is sufficient to revolve the pro- peller against its' greatly increased resistance to turning at the instant Lon reversing when the water flowing "past it (due to the motion of the ship). tends to keep it revolving, since the propeller then becomes a water turbine in effect, and it requires a prime mover with the characteristics of a turbine to overcome the greatly increased torque. oe When running at full power, the links of a reciprocating engine may be thrown over as rapidly as the steam can be shut off from the ahead and on the astern turbine, but even when the links have been thrown over, the engine does not respond immediately, but first stalls, until the drag of the propeller and resistance Though this is true, itis THE MARINE REVIEW volve in the opposite direction as soon as it has come to rest, SO that even if the time required to bring the pro- peller to rest were the same, the tur- bine would still have a considerable July, 1914 are obviated in the design adopted by the Westinghouse Machine Co, by the substitution of an impulse wheel for the high pressure portion of both the ahead and astern turbines. 4 3 UY FIG. 5 advantage. In general, an engineer would not dare to throw the links hard over, with full steam on, except in a very slow speed vessel of comparatively low power. What has just been said regarding - of the hull have checked the velocity 'to the point where the engine can 'Overcome the resistance of the pro- peller. In the turbine installation, however, the propeller Degins to re- KB ota 4d Ce Pigs the effect of the astern turbine on the economy increase of power of of the ahead turbine, particularly to. 4 applies complete more reaction _ turbine. Most of these disadvantages ub The Westinghouse Machine Co. has -used from 60 to 70 per cent of the full power ahead for the normal astern power where, in the opinion of the purchaser, it is deemed desirable, and in the case of Neptune approxi- mately 90 per cent of normal ahead power has been developed by the astern turbines. However, regardless of the normal astern power for which the turbine is designed, a_ greater proportion of the ahead power may be developed by using more steam, which as a rule, is available since the astern turbine is only in use at in- tervals. The use of the high pressure im- pulse wheel instead of reaction blad- ing' "in marine turbines, has two im- portant purposes... First, it. has = greater stopping torque, and_ second,