Under deck tonnage is the cubic contents of the vessel below the tonnage deck divided by 100. The tonnage deck is taken to the upper deck in ships that have less than three decks, and to the second deck from below in all other ships. Length is measured from the inside of the stem to the stern timber; and for each of the following classes of vessels is divided into different numbers of parts as follow--. 1st, 50 ft. long and under, 4 parts; 2nd, above 50 ft. and under 120 ft., 6 parts; 3rd, above 120ft. and under 180 ft.. 8 parts; 4th, above 180 ft. and under 225 ft., 10 parts; 5th, 225 ft. and upwards, 12 parts. Depth is taken from | of round of beam to the top of the ceiling on ordinary floors, and in others to the top of the ballast tanks, in which case the thickness of the ceiling is deducted. If the depth at the midship sectional division does not exceed 16 ft., divide it into four parts, and if it exceeds that length, divide it (and also the others) into six equal parts. The distances are then measured to the inside sparring; no measurements are taken to dunnage sparring. In oil vessels they are taken to the inside of the frames; and if a vessel is insulated for cooling purposes, to the sparring.

These measure-mentsare then put through Simpson's Rule to ascertain the cubic contents, and the result is divided by 10), which is the Board of Trade cubic equivalent for a ton, and then multiplied by 2 to complete the calculation for both sides of the ship, as one side only is measured. Gross tonnage is the addition of the under deck tonnage to that of the poop, or break, bridge-deck forecastle, chart house, deck houses, and hatches, if under 1/2 percent, of gross tonnage. In these the tonnage is found by dividing the cubic contents by 100. Galleys and engine houses are not added. Net register tonnage is the gross tonnage after certain deductions have been made. These are crew space, officers' rooms, and machinery space, which includes boiler room, engine room, and tunnel. An engine store or workshop is not include 1 in the machinery space. If the machinery space is above 13 per cent, and under 20 per cent, of the gross tonnage, deduct the tonnage of the machinery space plus 32 per cent, of it. If over 20 per cent., deduct If times the space measured. The deduction is to consist of the space actually occupied by or required for the proper working of the boilers and machinery. Engine and boiler spaces are measured to tonnage deck without light and air space.

When the 32 per cent, cannot otherwise be got, the light and air space is measured and added to the gross tonnage and to the machinery space. Light and air space is engine and boiler casings and engine skylight measured above the tonnage deck. The following examples will show how this works out. Tonnage for three-decked ship with laid decks: -

Under deck ..........

.....1,928.31

Poop .............

..... 132.04

Forecastle ..........

..... 55.68

Houses ............

..... 87.87

Excess of hatches .......

..... 2.24.

Gross Tonnage..........

.. 2,206.64

Deductions: -

Propelling space ...... - .

..... 706.12

Crew space ..........

..... 77.11

Total deductions .......

..... 783.23

Gross tonnage..........

.....2,206.64

Deductions ..........

..... 78323

Net Register Tonnage

..... 1,423.41

The tonnage co-efjicient is the tonnage divided by length multiplied by breadth by depth, divided by 100.

Example

The tonnage is 2,310: -

L x B x D /100 = 2,951 2,951) 2,310.

0.78 co-efficient.