Page:Popular Science Monthly Volume 92.djvu/560

 Boxes of Air to Foil the Torpedo

William T. Donnelly's ingenious method of making cargo-carrying ships unsinkable

By Robert G. Skerrett

��THE steamship Lucia is unsinkable. At least, such is the opinion of William T. Donneily, a consulting engineer of New York city and a member of the Ship Protection Committee of the United States Shipping Board. Indeed, this belief is shared by his associates on the Board, and for that reason Mr. Don- nelly's special system has been installed upon the ship in question.

The Boxes and What They Do

The invention consists fundamentally of a system of portable buoyant water- tight boxes, which, when packed in their designed places, form a veritable honey- comb of small air chambers. By thus greatly subdividing the space allotted to them, these boxes necessarily restrict the volume that may be opened up by the destructive gases of a torpedo, and, therefore, limit the amount of water that can enter the craft so damaged.

Maritime law sets a limit to a craft's deep load-line. The underwriters will not issue insurance if that line is sub- merged by reason of excess weight taken aboard. While this is a very necessary safety measure, still it actually invites peril. For instance, coal represents forty-three cubic feet to the ton while the ordinary baled cotton runs about ninety cubic feet to the ton. Clearly, if a steamer of a given capacity has her compartments entirely filled with cotton, when loaded to her prescribed water- line, those holds could not be more than partly filled when carrying a correspond- ing weight of coal. And because there would be that volume of unused space, when carrying coal, there would be just 80 much more room for water to rush in in case the hull were ruptured. This water would destroy the ship's reserve of buoyancy — previously represented by free air space — and cause her to sink. The cotton cargo, on the other hand, because it has less density and more bulk than the coal, would keep out the in-

��vading sea and actually buoy the vessel at the surface in spite of very serious injury to her hull.

Cargo Space Is Not Reduced Much

Now, Mr. Donnelly stows the smaller of his portable buoyancy chambers in between the ribs of the craft and up under the decks between the beams, holding the buoyancy boxes in place in both cases by means of wooden slats or "battens," as they are technically called. The boxes are placed where freight would not be packed. These safety chambers are what might be termed a permanent feature of his plan. In order to take care of excess space in the cargo holds, if the weight of the freight and its density are such that the compartments are not filled, the inventor resorts to "cargo boxes" which differ from the buoyancy boxes mainly in the matter of size. The buoy- ancy boxes average one foot by two feet by three feet and weigh one hundred and three pounds apiece; while the cargo boxes are two and one-half feet by two and one-half feet by six feet and weigh three hundred and eighty-seven pounds. The buoyancy boxes displace four hundred and sixty-five pounds of water, and the cargo boxes displace eleven hundred and fifty-three pounds of water — showing plainly a large net gain in reserve buoy- ancy. Every box is tested first for air- tightness by submerging it in a tank, and then for water-tightness by placing it in a sealed cylinder and subjected to hydro- static pressure corresponding to the posi- tion in the steamer.

The complete equipment of boxes for the steamer Lucia costs about one-tenth of the building price of the ship. Mr. Donnelly estimates that a vessel should normally be worth ten times her cost to her owners through the service she can render in the course of an average useful life. Therefore, his safety feature in- volves an outlay of only one per cent, of her probable returns.

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