THE ISLE OF MAN TWIN SCREW STEAMER TYNWALD.
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.
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.
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.