Vertical (compound) engines.
The vertical type of engine, with cylinders at the top and crank-shaft below,
was adopted for merchant ships long before it was introduced into the Royal
Navy, because it was a necessity in most warships that all the machinery should
be kept below the water-line, and horizontal engines alone satisfied this
condition. Figs. 7 and 8 show a vertical engine of the type fitted in the
mercantile marine.
Vertical engines possess many practical
advantages over horizontal engines, especially in connection with the
working of the cylinders and pistons, and general accessibility of the engine.
When, therefore, the twin-screw system was adopted for armour-clad ships,
vertical compound engines were fitted, with a middle line water-tight bulkhead
separating the two sets. By dividing the power into two parts, each set
of engines, even in a ship of great power, would be of moderate dimensions, and
although the whole of the machinery might not in all cases be entirely below
the water-line, the parts above would be protected, not only by armour plating,
but by a body of coal in addition, the coal-bunkers being continued on each
side of the engine room.
This extension of the use of vertical engines has continued and been applied to
all classes of vessel, and special means for protecting the cylinders have
often been fitted. At the present time new engines for the Navy are being made
vertical for all classes of vessel.
Three-cylinder compound engines
As the power of compound engines increased, the dimensions of the low-pressure
cylinders became so great that it was found desirable to fit two low-pressure
cylinders instead of one, in consequence of the difficulties experienced in
obtaining sound castings of large size, and to keep the size of the
reciprocating parts as small as possible. This led to what is known as the
three-cylinder compound engine, which is simply a modification of the ordinary
two-cylinder compound engine. Figs. 9 and 10 show a vertical compound engine of
the three-cylinder type.
