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Q. What is the advantage of a wooden underwater body?

A. It may be coppered, with the result that the ship does not foul quickly and may remain longer out of dock.

Q. Why could not a steel hull be covered with copper plates ?

A. The galvanic action caused by copper and steel in salt water would cause the huil of the vessel to corrode rapidly.

NOTE.—The few sheathed and composite ships that are in the Navy are of the gunboat or cruiser class. All the Denver type of cruisers, for example, are sheathed.

Q. What is nonscatterable glass?

A. One type is a single layer of glass, one face of which has received a coating of transparent elastic material. Another type has this transparent elastic

. material between two layers of glass.

Q. What precautions should be used with this glass?

A. Never use alcohol or solid washing compounds on the treated surface. Avoid handling the treated face with the bare hands.

Q. How are bulkheads shored up in case of damage?

A. Brace all shores with material running as nearly as practicable at right angles to the bulkhead to be supported. Do not brace one bulkhead by shoring to another unless there are supporting structures to distribute the load. Aim to shore bulkhead to a deck or vice versa. In general, the bulkhead stiffeners are the members to be braced."

Q. What are the tonnage rules?

A. There are five kinds of tonnage in use in the shipping business They are dead-weight tonnage, cargo, gross, net, and displacement tonnages.

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(a) Dead-weight tonnage expresses the number of tons (of 2,240 pounds) of cargo, stores, and bunker fuel that á vessel can transport. It is the difference between the number of tons of water a vessel displaces “light” and the number of tons it displaces when submerged to the load water line. Dead-weight tonnage is used interchangeably with dead-weight carrying capacity. A vessel's capacity for weight cargo is less than its total dead-weight tonnage. (6). Cargo tonnage is either “weight" measure

The weight ton in the United States and in British countries is the English long or gross ton of 2,240 pounds. In France and other countries having the metric system a weight ton is 2,204.6 pounds. A

measurement” ton is usually 40 cubic feet, but in some instances a larger number of cubic feet is taken for a ton. Most ocean package freight is taken at weight or measurement (W/M), ship’s option.

(c) Gross tonnage applies to vessels, not to cargo. It is determined by dividing by 100 the contents, in cubic feet, of the vessel's closed-in spaces. A vessel ton is 100 cubic feet. The register of a vessel states both gross and net tonnage.

(d) Net tonnage is a vessel's gross tonnage minus deductions of space occupied by accommodations for crew, by machinery for navigation, by the engine room, and by fuel. A vessel's net tonnage expresses the space available for the accommodation of passengers and the stowage of cargo. A ton of cargo in most instances occupies less than 100 cubic feet; hence the vessel's cargo tonnage usually exceeds its net tonnage, and may in some instances exceed the gross tonnage.

(e) Displacement of a vessel is the weight, in tons of 2,240 pounds, of the vessel and its contents. Displacement "light" is the weight of the vessel without stores, bunker fuel, or cargo. Displacement “ loaded” is the weight of the vessel plus cargo, fuel, and stores.

(f) Example. For a modern freight steamer the following relative tonnage figures would ordinarily be approximately correct: Net tonnage

4, 000 Gross tonnage

6, 000 Dead-weight carrying capacity

10, 000 Displacement, loaded, about

13, 350 Q. What protectors are used on steel plating of hull near composition fittings to prevent pitting from electrolytic action?

A. The practice of fitting zinc protectors on the steel plating of the hulls of vessels, in the vicinity of composition sea valves and chests, composition torpedo and tube mouthpieces, on rudders, shaft tubes, and struts, and near propellers as a protective measure against electrolytic action has now been largely abandoned except in cases of destroyers and submarines.

48406°--28_20

CHAPTER 24

SUBJECT G.GENERAL FEATURES OF SHIPS

OF THE NAVY OF DIFFERENT CLASSES

CLASSIFICATION OF VESSELS IN OUR NAVY

The classification of vessels in our Navy is as follows:

(a) Battleships, first line.—All our 18 battleships now allowed us by the Washington Conference belong in this class.

(6) Cruisers, second line. This includes the Rochester, Pittsburgh, and St. Louis classes of cruisers.

(c) Light cruisers, first line. This includes the Omaha class and will include all new cruisers now authorized similar to Omaha class up to 10,000 tons displacement, such as the Pensacola and Salt Lake City.

(d) Light cruisers, second line. This includes the Chester and Denver classes and the Olympia.

(e) Aircraft carrier, first line.—This includes the Saratoga class of carrier.

Aircraft carrier, second line.-Langley. (9) Mine layers, first line.- None of these are on the Navy's list at present.

(h) Mine layers, second class.—This includes the Baltimore and Shawmut classes.

(i) Destroyers, first line.-All our 1,000 and 1,200 ton destroyers.

(j) Destroyers, second line. All our 750-ton destroyers.

(K) Submarines, first line.Submarines of the s class.

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