The Mercury (Hobart, Tas. : 1860 - 1954)(about) |
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Saturday 23 November 1912
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2 corrections, most recently by SunderlandSite - Show corrections
SHIPS WITH CORRUGATED
HULLS.
SUCCESSFUL EXPERIMENTS.
The Ericsson design of ship, having the shell-plating arranged with two longitu- dinal corrugations along the side between the water-line and the turn of the bilge, is steadily growing in favour. The first ship-the Monitoria-built, like her suc- cessors, by Messrs. Osbourne, Graham and Co., Sunderland, has been running for three years; the second-the Hyltonia -for one year; the third was launched in May last¡ the fourth in July; and two others are in course of construction; while a seventh is being built in Nor- way. The results of the working of the two completed ships, and the confidence disclosed in ordering the others, justifies some examination of the claims set np for the design, and it was not, therefore, inappropriate that these should be dealt with in a paper read at the Royal United Service Institution by Captain G. S. Mac- Ilwaine, R.N. (retired). He had made several voyages in one of the ships with a view to forming an independent judg- ment ef the merits ef ths case, and the
aim of his paper was that the system should be considered bv the Admiralty.
This consideration he justified on the score of increased strength, specially call-
ed for in the case of destroyers; greater resistance to penetration bv projectiles, obtainable even in the case of armoured ships, especially when the ship was roll-
ing in a heavy sea dunng action; and higher propeller efficiency, consequent on superior streamlines due to the corruga- tions. The admiralty are no doubt fully cognisant of the features and potentiali- ties of the design; but Captain Mac- Ilwaines's statement of the case will be useful to Navy officials as well as to ship-
owners.
The Hyltonia is representative of the system. She is 279ft. long between per- pendiculars 39ft. 10in. beam, 18ft. draught with 3ft. freeboard, and carrv- ing 3,340-tons dead-weight she displaces 4,614 tons. The net registered tonnage is 1,149 tons. There are in her case, two corrugations fore and aft, the width from the top of the upper corrugation to the bottom of the lowei being 13ft. 3in., and from the inner edge of the frames the corrugations project 22in. Forward and aft the corrugations taper to merge into the normal lines of the hull. Before deciding to build tho ship, the owners carried out some tests with models in a tank on Caw's pendulum system. Models of plain and corrugated ships, without other variants, were floated and attached pivotally to a pendulum first held at a known anglo to the vertical by the model being secured in the tank to a cord. By the burning of the cord the model was gently released and the amplitude of swing of the pendulum determined the comparative resistances of models. The results suggested possibilities of "a re- duction in effective horse-power of from 14 to 23 per cent." The claim made is that "the space between the corruga- tions seems to act as a conduit pipe sup- plying the screw, which in its turn, seems almost to play the part of a pump drawing a solid bodv of water along the ship's side in which to work." In other words, that the stream- lines are better, the water being less disturbed. Captain MacIlwaine said that the blades of the propeller could be seen rotating at all speeds as clearly as through crystal. The data of actual performances showed that when tho corrugations were fully im- mersed the slip of the propeller averaged less than 2 per cent., as against 13 per cent. for ordinarily plated ships of the same design. The average revolutions in the corrugated ship was 58, tho power 630 indicated horse-power, the normal speed about 9 knots, and the fuel con- sumption when loaded, 10.8 tons of Lan- cashire coal per day. For the same duty with the plain plated ship the power ne- cessary was 700 to 750 indicated horse- power, and the consumption 12 tons per
day.
It was claimed, too that the corruga- tions add to strength. In the Hyltonia every alternate frame was left out under the highest classification of the British Corporation, so that the frames were 48in. apart, as compared with 23½in. in ordi- nary ships ot the same size; this, and the absence of stringers, effected a saving of
50 tons m weight. Again as tonnage
measurement is from the inside of the framing, there is increased cargo-space without tonnage dues being exacted, for the space given by bulging out in the corrugated plates is not reckoned. The same considerations facilitate inspection and the handling of cargo. Increased steadiness at sea and greater stability were also claimed, and results were given of sea-behaviour. In one voyage the deck portion of a cargo of timber was 43 per cent. of the whole, the average height of tho deck cargo being 18ft,; on another occasion the figures were 45 per cent. and 19ft respectively. 428 tons of water bal-
last being carried in the tanks. It was also contended that vibration was reduc- ed, and steering made easier, while the constructional cost was about the same - "Engineering. "