We place on record the details of the first high speed twin screw
steamer built for the service. Of this vessel, named the Tynwald, we
give a profile and an engraving of stern, showing the method of
supporting the brackets for propeller shafting.
[Illustration: Twin screws--rear view]
The Tynwald is 265 feet long, 34 feet 6 inches beam, and 14 feet 6
inches depth moulded, the gross tonnage being 946 tons. The desire of
the owners to put the vessel alternately on two distinct services
required special arrangement of the saloons. Running between Liverpool
and the island there was no necessity for sleeping accommodation, as
the passage is made in about three hours; and the ship had to be
suited to carry immense crowds. But as the owners wished on special
occasions to run the vessel from Glasgow to Manxland it was necessary
to so arrange the saloons as to admit of sleeping accommodation being
provided on these occasions. On the Liverpool run the vessel will
carry from 800 to 900 passengers. A spacious promenade is an
indispensable desideratum, and the upper or shelter deck has been made
flush from stem to stern, the only obstructions in addition to the
engine and boiler casings, and the deck and cargo working machinery,
being a small deck house aft with special state rooms, ticket and post
offices, and the companion way to the saloons below. On the main deck
forward is a sheltered promenade for second class passengers, while on
the lower deck below are dining saloons, the sofas of which may be
improvised for sleeping accommodation. At the extreme after end of the
main deck is the first class saloon, with the ladies' room forward on
the starboard side, and, there being no alley way forward, the ladies'
lavatories are provided on the starboard side of the engine casing. On
the port side are the gentlemen's lavatories, and smoking saloon and
bar. The dining saloon is aft on the lower deck, with ladies' room
forward. In the two saloons and ladies' rooms sofa berths can be
arranged to accommodate 252 passengers. The crew and petty officers
are accommodated in the forward part of the ship. As the profile
shows, the vessel is divided by transverse bulkheads into seven
watertight compartments, and there are double bottoms. She has six
large boats and several rafts.
[Illustration: THE LIVERPOOL AND ISLE OF MAN TWIN SCREW STEAMER
TYNWALD.]
The twin screws are revolved by separate triple expansion engines,
steam being supplied by two double-ended boilers. Each boiler is
placed fore and aft, and each has a separate uptake and funnel. There
are three stokeholds, and to ventilate them and supply sufficient air
for the furnaces there is in each a 6 foot fan driven by an
independent engine running at 250 revolutions. These have been
supplied by Messrs. W.H. Allen & Co., London. The boilers are of steel
and adapted for a working pressure of 160 lb. to the square inch. They
are 16 feet in diameter and 18 feet long, and there are eight furnaces
in each boiler, sixteen in all, the diameter of each furnace being 3
feet 4½ inches.
The cylinders of the main engines are 22 in., 36 in., and 57 in. in
diameter respectively, with a piston stroke of 3 ft. The high-pressure
cylinders are each fitted with a piston valve, and the intermediate
and low-pressure cylinders with double-ported slide valves, all of
which are worked by the usual double eccentric and link motion valve
gear, by which the cut-off can be varied as required. All the shafting
is forged of Siemens-Martin mild steel of the best quality, each of
the three separate cranks being built up. The condensers are placed at
the outsides of the engine room, and the air, feed, and bilge pumps
are between the engines and the condensers and worked by levers from
the low-pressure engine crosshead. There are two centrifugal pumps,
each worked by a separate engine for circulating water through the
condenser, and these are so arranged that they can be connected to the
bilges in the event of an accident to the ship. In the engine room
there is fitted an auxiliary feed donkey of the duplex type and made
by the Fairfield Company.
This pump has all the usual connections, so that it can be used for
feeding the boilers from the hot well, for filling the fresh water
tanks, for pumping from the bilges, or from the sea as a fire engine.
The engines are arranged in the ship with the starting platform
between them; and the handles for working the throttle valves,
starting valves, reversing gear (Brown's combined steam and
hydraulic), and drain cocks are brought together at one end of the
platform, so that the engineer in charge can readily control both
engines. The two sets of engines are bound together by two beams
bolted to the framing of each engine. This feature was introduced into
the design for steadiness.
The method of supporting the propeller shaft brackets is interesting,
and we reproduce a photograph that indicates the arrangement adopted.
Instead of the A frame forming part of the same forging as the stern
frame, the Fairfield Company have built up the supporting arms of
steel plates riveted together, as is clearly shown. There is an
advantage in cost and with less risk in undiscovered flaws in
material.
An interesting change has been made in the steam pipes. Cases of
copper steam pipes bursting when subjected to high pressure have not
been infrequent, and Mr. A. Laing, the engineering director on the
Fairfield Board, with characteristic desire to advance engineering
practice, has been devoting much attention to this question lately. He
has made very exhaustive tests with lap welded iron steam pipes of all
diameters, but principally of 10 in. diameter and 3/8 in. thickness of
material, made by Messrs. A. & J. Stuart & Clydesdale, Limited, and
the results have been such as to induce him to introduce these into
vessels recently built by the company. It may be stated that the pipes
only burst at a hydraulic pressure of 3,000 lb. to the square inches.
The Tynwald was tried on the Clyde about a month ago, and on two runs
on the mile, the one with and the other against the tide, the mean
speed was 19.38 knots--the maximum was 19½ knots--and the indicated
horse power developed was 5,200, the steam pressure being 160 lb., and
the vacuum 28 lb. Since that time the vessel has made several runs
from Liverpool and from Glasgow to the Isle of Man, and has maintained
a steady seagoing speed of between 18 and 19 knots.--_Engineering._
* * * * *