These improvements in many instances pertain to the engine builder’s duties, and are questions which I think have been treated lightly; notably that of insufficient bearing surface, and one of the principal causes of hot bearings, whereby the oil intended for lubrication was squeezed out, and the metal surfaces brought too close in contact; and when bearings had a pressure of 200 lb. per square inch, it has been found that not more than 120 lb. per square inch should be exerted to keep them cool (this varies according to the material of which the bearing is composed), without having to use sea water and prevent them being ground down, and thus getting out of line.  I have known a bearing in a new steamer, in spite of many gallons of oil wasted on it, wear down one-eighth of an inch in a voyage of only 6,000 miles, from insufficiency of bearing surface.

Several good rules are in use governing the strength of shafts, which treat of the diameter of the bearings only and angles of the cranks; and the engine builder, along with the ship owner, has been chary of increasing the surfaces by lengthening the bearings; for to do this means increase of space taken up fore and aft the vessel, besides additional weight of engine.  Engine builders all aim in competing to put their engines in less space than their rivals, giving same power and sometimes more.  I think, however, this inducement is now more carefully considered, as it has been found more economical to give larger bearing surfaces than to have steamers lying in port, refitting a crank shaft, along with the consequences of heavy bills for salvage and repairs, also the risk of losing the steamer altogether.  Proportioning the bearings to the weights and strains they have to carry has also been an improvement.  The different bearings of marine engines were usually made alike in surface, irrespective of the work each had to do, with a view to economy in construction.

In modern practice the after bearings have more surface than the forward, except in cases where heavy slide-valve gear has to be supported, so that the wear down in the whole length of the shaft is equal, thus avoiding those alternate bending strains at the top and bottom of the stroke every revolution.  Another improvement that has been successfully introduced, adding to the duration of life of crank shafts, is the use of white bearing metal, such as Parson’s white brass, on which the shafts run smoothly with less friction and tendency to heat, so that, along with well proportioned surfaces, a number of crank shafts in the Peninsular and Oriental Co.’s service have not required lining up for eight years, and I hope with care may last till new boilers are required.  Large and powerful steamers can be driven full speed from London to Australia and back without having any water on the bearings, using oil of only what is considered a moderate price, allowing the engineer in charge to attend to the economical working of both engines