Fresh water weighs 62.5 lbs. per cu. ft., and is taken at 36 cu. ft. per ton.

Example: A ship having 1200 tons displacement, 12′ 6′′ mean draft in sea water, and 6 tons per inch immersion at this draft; what would be her draft in fresh water?

First find volume displacement in fresh water, which is 1200×36 43200 cu. ft. From this, subtract volume displacement in sea water, which is 1200 × 35=42000 cu. ft. 43200-42000=1200 cu. ft., which is volume of layer or water -plane between fresh and sea water drafts.

As the tons per inch immersion at this draft are 6; then the change in draft in inches = × 1200÷36=5.5 in.; 5.5" + 12′ 6′′ 12′ 11.5" draft in fresh water.

CHAPTER II.

MISCELLANEOUS SUBJECTS PERTAINING TO ALL

TRADES.

(Represented in the Deck Artificer Branch.)

METHOD OF NUMBERING WATER-TIGHT COMPARTMENTS.

[Approved by the Department in its indorsement of Oct. 10, 1912, No. 8557-118, C. & R. No. 500A 135.]

Principal Divisions.-The ship shall be considered as divided into four principal divisions, lettered A, B, C and D, from forward aft.

Division A.-This shall comprise all the space between the stem of the ship and the forward transverse bulkhead of the forward boiler compartment.

Division B.-This shall comprise all the space between the forward transverse bulkhead of the forward boiler compartment and the after transverse bulkhead of the after boiler compartment, or where boiler compartments are located forward and aft of engine rooms, it shall comprise all the space between the forward and after transverse bulkheads of the forward group of boiler compartments and between the forward and after transverse bulkheads of the after group of boiler compartments.

Division C.-This shall comprise all the space between the after transverse bulkhead of the after boiler compartment and the after transverse bulkhead of the after compartment assigned to main propelling machinery or auxiliaries of main propelling machinery, or where boiler compartments are located forward and aft of the engine rooms, Division "C" shall comprise all the space between.

Division D.-This shall comprise all the space between the after transverse bulkhead of the "C" (or "B") division and the stern of the ship.

These divisions shall be considered as extending from the keel to the highest deck in the line of the bulkheads, or the bulkhead prolonged. In case the bulkheads do not extend to the highest deck any spaces between decks that extend through two of the principal divisions shall be numbered as described. in the case of a compartment situated entirely in the forward division of the two in which it is placed, and shall have this number alone.

Rules for Numbering.-All numbers in each division shall begin at the forward end of that division. The forward compartment of the double bottom in each division shall be A-1, B-1, C-1, or D-1, according to its respective division. The space next above the inner bottom, and the hold compartments where there is no inner bottom, shall be, starting from forward as above, A-101, B-101, C-101, or D-101, according to its division. Each successive level shall have a new series of numbers always beginning with the next hundred. The greatest number of levels (i. e., decks, platforms, etc.) existing anywhere in the ship shall determine the highest series of hundreds to be used. By this method all compartments on a given level will have numbers in the same hundreds series. Where a platform or deck steps down less than a deck height, no change in the hundreds series shall be made on account thereof.

Compartment Letters.-The numbering of the compartments shall be prefixed always with the letter indicating the general division of the ship in which it is placed, as A-21, B-3, etc. All magazines, projectile rooms, ammunition rooms, torpedo warhead room, etc., containing explosives of any kind. shall have the letter M after the number of the compartment. Compartments on the starboard side of the ship shall have odd numbers; those on the port side, even numbers.

Fig. 22 illustrates the general distribution of the numbers. and divisions.