MAGIC IN STEAMERS.

Dominion, Volume 3, Issue 823, 23 May 1910, Page 8

MAGIC IN STEAMERS.

THE DEGIDINC POINT IN THE DUCO CASE. [Br Gyro.] Who hath desired the Sea? Tho immense and contemptuous surges? Tho shudder, the stumble, the swerve, As the star-stabbing bowsprit emerges? Man's Sea in no wonder the sameMan's sea, and the same through each wonder: Man's Sea as she serves him or kills. Of the beautiful steamers which flit through the soft blues that fringe our coasts none is pleasanter, perhaps, to travel in than Mokoia. And in rough weather few can plug through more steadily than Navua. Yet, in neither of these boats is the intensely interesting thing that settled the Duco case — metacentric height—remarkable. Little Patoena, too, is so balanced in her measurements that in a stiff sea (in normal trim) she is as steady a ship as a king might desire. To jump off thp train at Lyttclton on a night when the sea is thundering in under Godley Head, and the doleful wind whistling through the funnel guys, it.

is indeed pleasant to recolloct that it happens to be Pateena which is bearing you and your fortunes northward to Wellington, and not some more imposing blur of tier upon tier of golden light. That is, if you understand metacentres, and their somewhat cranky relation to sea sickness. ' When Mr. T. E. Taylor, M.P., heaped obloquy on this fine boat last session he was doing what the average politician is always doing—preaching from a test chosen from the vast, fatuous gospel of Rule of Thumb. One surmises, however, that rule of thumb is now a's dead as a door nail for future marine cases relating to stability of ships. Consciously or unconsciously. Mr. C. P. Skerrett killed it last week in the Duco case. Mr. J. H. Hosking, his opponent, is a very able barrister, and what ho does not know about marine cases is hardly worth knowing, but Mr. Skerrett's two calm experts, with their calculations, brought a white light into tho witnessbox and the Court blinked. It was a tour-do-force in evidence, although to be sure the proceedings only arrived on the bare edge of metacentric magic. Unseen, but mighty in their action, as the haul of a thousand horses, three

points lurk deep in every ship. Tho merciless dog-hooks, which bewray the importer's merchandise, clutch and claw through them, tho lumper toiling in the hold jostles against them, and chunks of pig-iron drop incontinently from crazy slings, annihilating all but them. Even the wild diction of the chief officer, who is "describing" his unspeakable agents and tho umooked-for heap of cargo which has been wheeled down to the ship's side after she has been trimmed, cannot hurt them. Unassailable, invisible, these three noble, mighty fellows—the Wonder Point, Point Stolid, and Point Neutral—keep watch and ward over the ship, too proud to notice tho dog-hooks or tho tailing iron, for their activities are not the activities of the wharf, and great aristocrats that they are, they turn disdainful noses upward at the mere mention of "trade." Only when the ridged grey of the Strait tangs and thunders on the plates, and the ship wearily lifts her fore-foot to tho wot, inrolling walls of the storm do they "strip to it," and set their strong forces into play. White water half-guessed overside, And tho moon breaking timely to bear it, Alan's Sea as his fathers have dared, Man's Sea as his children shall daro it, Man's Sea as she serves him or kills. But, serve or kill, the sea can only touch the ship in the matter of stability through the three invisible points and, moro particularly, tlirough the Wonder Point. Through that point, the strong hand of old ocean can only push one way—vertically upwards. The weight of the ship, too, can only push one way—vertically

downwards through Point Stolid. Point Neutral is the .faithful pivot round which these forces play. The blacklines in the second and fourth sketches show tho puissant, ghostly machinery at work, and the direction of tho arrows indicates what way tho forces are pulling. It is really a lover, pivoting round Point Neutral. In the case of s.s. Unimpeachable (figure 2) the forces are pulling the right way and the ship will presently rise on an oven keel. Furthor inspection of tho sketches will show, however, that while tho Wonder Point is the "bright boy" of the class, ho is also the most conscious of his dignity. If he is not kept on top—and always on top—he forms a somewhat sulky, and altogether unholy alliance with the sea. to capsize tho ship. And it is regrettable that, when ho does stoop to this rile business, ho finds a slow, bill, heavy ally in Point. Stolid. I The trouble is that every lon nf cargo nlaccd on board affects our briglit

friend's position. If pig-iron is stowed ovor the. bilges and kapok just under hatches the Wonder Point, like a sentient being, is pleased, because that style of stowage enables him to keep his ascendancy over his two plebeian brothers. On the other hand, if tho order of Btowing should be unwisely reversed, so that the light cargo is down low and the heavy material on deck, tho Wonder Point, (being a hydrostatic variable) may sink below tho other two. In that case he "takes the law into his own 'hands."

In the lirst sketch of s.s. Unimpeachable he is on top, and when tho ship is rolling, as in skotch 2, he works hard to right her. But in the third skotch —that of s.s. Outrageous—he has sunk

below the other points for some reason or other, and in sketch 4 he is out for mischief with a heart full of black intent. The force of the water is still vertically upwards through him, and the weight of the ship is still vertically downwards through Point Stolid, but the direction of the leverago is reversed now, and s.s.. Outrageous is about to capsize, for both forces, shown by the arrows, are pulling that way. '

The great point in marine architecture, therefore, is to keep the metaeontre (which is the Wonder Point) in the ascendant oyer Point Stolid which is the vessel's centre of gravity. Tho other point—Point Neutral—is known in hydrostatics as "the centre of buoyancy."

Altogether it is a very interesting subject and the case of the Duco probably marks its first appearance in a New Zealand Court. The world is really moving, and every day sees some new nail driven into the coffin of Rule of Thumb. When the two experts in Court figured out the metacentric height of the Duco—that is tho height of the Wonder Point above Point Stolid—and found it to be sufficient, the last word on the little boat's stability had been said.