PROPELLER SHAFTS.

New Zealand Mail, 18 January 1900, Page 14

PROPELLER SHAFTS.

THE ACHILLES’ HEEL- OF MODERN SHIPS.

(By F! T. Bulion in_ tho “Morning Leader.”)

It was Well said in a leader of tho “Sbippmg Gazette recently that the breakdown or the transport Persia, serves to eaii public attention prominently to a subject which has tor some time past been engaging serious notice m the shipping wo rid. For 'twas ever thus—a condition or things in public policy or a- great industry may exist for many years of the utmost menace to the well-being of a vast number of people, yet the -voices e£ the warmers go forth incessantly into irresponsive silence. At length there comes a day when, by means 'of a great disaster' (in the Persia’s case most happily just averted), tho lethargic monster we call the Public wakes up, turns himself, and demands that something be done. SEVENTY-FOUR IN A HALF-YEAR. ! New the subject of the leader in ; question was the breaking of propeller shafts, an accident which, if it befalls 1 a huge modern steamship in mid-ocean, ] leaves her just a log upon the sea. In ] few cases does it end in serious damage to the vessel, but the amount of < public anxiety and tho loss in hard < oasb it causes are enormous. ■ Few indeed of the travelling public : are aware how large a number of these 1 accidents occur. The committee of Lloyd’s Register recently compiled a list i of some of the accidents to shafts of < steamers amounting to a complete breakdown, which they circulated among those interested in the subject, inviting suggestions and observations. It must have come as a startler to many to find that during the first half of the present year no less than 74 steamships, the great majority of which were of large size, suffered this serious disaster. WHAT A SHAFT BREAKAGE MEANS Of course there is a goodly minority among newspaper readers who know exactly what is meant by a steamer’s breaking her shaft, but for the benefit ; of the majority who do not, it may be c necessary, in order to show how the i accident* is brought about, to_ give a i few words of explanation as simply as i may be. Nearly all steamships have c their engines at a considerable distance $ from the propellor, the lour or three s bladed screw which, according as it 5 is turned, thrusts the hull forward or i draws it backward. The connection between the engines f and tho propellor is made by means of c a solid cylinder of steel passing through s bearings lined with gun-metal gone rails - , 1 and kept cool by a stream of water 1 Sowing over them outside, and a lib- 1 eral supply of some lubricant, usually 1 tallow, inside. Now, it does not need 1 much wit to understand that the twisting stress upon these long shafts of c steel is at all times very great, need- I ing them to be of the most flawless r composition in order tliat they shall C be dependable. c Suqfi is the care taken in their manu- r facture that it may safely be said that v if they were only subjected to the steady, equable strain of the engines l upon them there would scarcely be a a case of a shaft fracture heard of. But e such a state of. things is unthinkable at t sea. In rivers, of course, but op. the a ocean the frequent occurrence of gales s of wind and consequent heavy seas r brings about such an alteration of the conditions of service of the staff that it is marvellous how few relatively of . these accidents do occur. I HOW IT HAPPENS. ' * When even the heavily-laden steam- a ship, with her propellor so far beneath f the surface of the sea as to be out c of sight, meets with a hc-avy gale g ahead, raising a succession of confront- jing waves, she must of necessity pitch q and dive'tremendously. lii so doing it ( is inevitable that she will occasionally j lift her propellor out of the - water suddenly, while the full drive of the \ engines are being; exerted -upon s<i it. £ What this means to every part - of the machinery can only bo imagined by a e layman (a non-engineer), The -sudden ( leap from the solid resistance of the c water into the non-resistance of the air a is a change of condition so great that G not even the most cunningly devised > ‘ governor” can do more than attempt o to modify its severity. w It is instantly followed by : a return a to the former strain with a wrench that c seems sufficient to strip the’ mighty v blades of metal from the propellor as s if they were feathers in a shuttlecock. The “governor” mentioned comes to the n relief of the sorely-tried mechanism' bv t automatically shutting off the supply ( of steam with the cessation of strain, I and turning it on again as the propellor plunges into its proper elements. .. But the changes are so instantaneous, 0 the pressures are so enormous, that a b tiny flaw, a slight weakness, is almost e sure to be fatal. Perhaps not in that c gale, but in the next. c DANGEROUS TO THE LOADED AND EMPTY. If this be so in a loaded steamer, h how much more is it so in a light o one. Experts are at one in consider- t ing that from this cause alone, ai- J

though there axe others that cannot now be touched upon, an underloaded steamer is quite as unseaworthy as an overloaded one. How often does one pass a large steamship coming down Ohanivd bound oversea, and notice that even in the smoothest water nearly half of her propeller is idly beating the air. Just a little head sea gets up, and that vessel’s engines', shaft, and propehor aro immediately subjected to a succession of shocks that make their escape from damage almost' a miracle. Then it is that the engineer’s lot, never a light one, becomes truly terrible in its burden. He knows in his innermost fibre all that is going on, the potentialities of disaster there are in every' plunge of the ship’s stern, from its high poise on the back of a sea clown into the weltering valley between —knows, too, what lies before him and his trusty helpers if the shaft should break, if the engines should go to smash. ENGINEERS’ “ROLL OF HONOUR” WANTED. No warrior ir. the deadly breach ever showed more perfect courage cr reached a higher plane- of self-sacrifice than does the marine engineer, and that not as a mere episode of his calling, but almost continually. What apparent miracles have been wrought by these sons of steel at the call of duty and under the most terrible circumstances we need an engineers’ “roll of honour’’ to teach us—not that any public recognition of their worth could possibly add to the fidelity and heroism continually manifested by them. One word, in conclusion, on an unfavourable comparison, which has been drawn between men-o'-war and merchant steamers, unfavourable to the latter on account of the almost complete immunity from shaft breakages of the former. The comparison is unfair and should never have been made. The load-line of a warship is almost a fixed quantitv. This has, perhaps, more to do with shaft fracture than aught else.