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 and boilers (as well as many other engines of
all kinds now placed on board a large mail and passenger steamer),
instead of getting many a drenching with sea water, and worried by
close attention to one or two hot bearings all the watch. Compare
these results with the following: In the same service in 1864, and
with no blame to the engineer in charge, the crank shaft bearings of a
screw steamer had to be lined up every five days at intermediate
ports, through insufficient bearing surfaces. Sea water had
continually to be used, resulting in frequent renewal of crank shaft.
Steamers can now run 25,000 miles without having to lift a bearing,