DISCUSSION ON MAY MEETING PAPERS. 31 



this reason the low-speed gear bearings should be made very ample, and the clearances should 

 be made as small as possible. 



In a number of recent ships, principally British, the thrust bearing is located well abaft 

 the gear and is carried on a heavy foundation which forms part of the gear foundation. This 

 arrangement has the advantage that the steady bearings contained in the thrust bearing will, 

 if closely fitted, help considerably in preventing the shafting from throwing the gear out of 

 line. The same result can be obtained by using one or two heavy steady bearings with 

 closely fitted caps carried on strong foundations abaft the gear. Where the machinery is 

 located in the stern, this precaution is of still greater importance. 



Referring to page 15 of his paper, Mr. Warriner observes that heavy weather conditions 

 at sea are very different from the normal conditions and that the pressures on the gear teeth 

 are greatly increased under such conditions. This statement was fully borne out by actual 

 observation on the Neptune, which was equipped with a Westinghouse hydraulic dyna.- 

 mometer which indicated continuously the load on the teeth of the gear. In heavy weather it 

 was observed that the average pressure increased considerably and that there was a con- 

 stant and large fluctuation in pressure, which varied with the rolling and pitching of the 

 vessel. 



In ordinary heavy weather the average dynamometer pressure increased to 84 pounds, 

 which was 24 per cent above the pressure of 68 pounds at the same revolution per minute, 

 with a light wind and a fairly smooth sea. The variation in pressure was about 20 pounds 

 above and below the average. In very heavy weather the increase was still greater, and, as 

 I recall, the maximum pressure was well over 50 per cent above normal. In both cases, how- 

 ever, the revolutions were from 15 to 20 per cent below the designed. 



It is my conclusion, from the observation of gear operation in heavy weather, that con- 

 servative tooth pressures should be used and that gearing should be able to stand continuous 

 operation at pressures well above the designed maximum. This allowance will of course 

 depend on the type, speed and service of the vessel. For ocean merchant vessels I would 

 suggest an allowance of about 50 per cent based on continuous land operating conditions. 



Referring to Mr. Warriner's remarks on page 16 and to Figs. 4 and 5 on Plate 5, the 

 requirements for dividing the load equally between the low-speed pinions are very difficult, 

 and for this reason a very large margin of flexibility should be allowed. This type of gear 

 has given a great deal of trouble, a large part of which appears to have been due to inade- 

 quate flexibility for the proper division of the load. 



In general a single turbine with these types of gears is not desirable for large vessels. 

 Cross compound turbines with gears as shown in Figs. 6 to 9 have advantages in safety, 

 reliability and economy which make this type of unit desirable in all except vessels of small 

 power. This type has been used in most recent vessels and in general may be regarded as 

 the standard type for practically all ocean merchant vessels. 



On page 17 Mr. Warriner advocates the use of cast-steel wheels with teeth cut in the 

 rims. I seriously doubt the advisability of this type of construction. It is believed that a 

 cast-iron center with a rolled steel rim is more reliable and preferable. One of our vessels 

 recently had a serious breakdown at sea due to a defective cast-steel wheel. A section of 

 the wheel rim 20 inches on the chord broke off from the high-speed gear wheel when the 

 vessel was approaching the Panama Canal en route to New York. Fortunately the low- 

 speed gear and the starboard high-speed gears were not damaged, and the vessel proceeded 

 to New York under the high-pressure turbine only, the speed being reduced from 1 1 to 9.4 



