The author then briefly described the modern marine engine and boiler.
The three great types of compound engines may be placed as follows in
the order of their general acceptance by the shipowning community: (1)
The two-cylinder intermediate-receiver compound engine, having cranks at
right angles. (2) The Woolf engine in the tandem form, having generally
the high-pressure and low-pressure cylinders in line with each other,
but occasionally alongside, and always communicating their power to one
crank. Such a pair of engines is used sometimes singly, oftener two
pairs together, working side by side to cranks at right angles; recently
three pairs together, working to cranks placed 120 deg. apart. The
system affords the opportunity of adding yet more engines to the
same propeller to an indefinite extent. (3) The three cylinder
intermediate-receiver compound engine, with one high and two
low-pressure cylinders, the steam passing from the high-pressure
cylinder into the receiver, and thence into the two low-pressure
cylinders respectively. The cranks are placed at equal angles apart
round the crank shaft, so as to balance the forces exerted upon the
shaft.
These three types may be said to embrace all the engines now being
manufactured in this country for the propulsion of steam vessels by the
screw propeller. In their leading principles they also embrace
nearly all paddle engines now being built, whether the cylinders be
oscillating, fixed vertically, or inclined to the shaft.
The compound engine, in fact, in one of these three forms, may now be
said to be universally adopted in this country; and the question of the
relative value of simple expansion in one cylinder, and of compound
expansion in two or more cylinders, which agitated the minds of some of
our leading engineers ten years ago, is now practically solved in favor
of the latter.