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TRIPLE COMPOUND ENGINES.

[Footnote: Paper read before the Institution of Naval Architects, March
27, 1885.]

By Mr. A.E. SEATON.

My attention was first called to the modern triple compound engine by the
published reports of the trial trip of the yacht Isa, and in it I plainly
discerned the germs of a successful new type of engine; but it was not
until I had seen the engines of the screw steamer Aberdeen erected in the
workshops of Messrs. Robert Napier & Sons that I became convinced that it
was the engine of the immediate future. It is, however, due to the
farsightedness and enterprise of Mr. C.H. Wilson, M.P., that I was
enabled to try the merits of the new system and compare it with the old.
Mr. Wilson had already viewed the triple compound engine with more than
ordinary interest, and it required little persuasion on my part to allow
the company to which I have the honor to belong to construct a triple
expansion engine in lieu of the ordinary compound for one of four sister
ships which it then had in hand for Messrs. Thomas Wilson, Sons & Co.,
the latter only stipulating that it was to be of the same power as the
engine already contracted for. As I was quite convinced that economy was
due to the system rather than to the higher pressure, it was decided not
to increase the boiler pressure more than was necessary to suit the
triple system. The other three ships already alluded to were being fitted
with engines having cylinders 25 inches and 50 inches diameter by 45
inches stroke, and supplied with steam of 90 lb. pressure from a double
ended boiler 13 feet 9 inches diameter by 15 feet long, having a total
heating surface of 2,310 feet, so that these engines have every
qualification for being economical so far as general proportions go, the
stroke being an abnormally long one and the boiler of ample size.
Experience has since shown that these engines are economical in coal,
and the wear and tear exceptionally small.

The new engines for the fourth boat were made with considerably shorter
stroke, and the cylinders proportioned so as to give equal power; they
are 21 inches, 32 inches, and 56 inches diameter by 36 inches stroke, the
high pressure cylinder being supported on columns immediately over the
medium cylinder, and in other respects these engines were made as near as
possible like the other ones above named. Steam at 110 lb. pressure is
supplied from a doub