Artikel 45

The cubic capacity of each double-bottom tank, which must be known when determining the maximum allowance for water-ballast spaces (see Article 71), is to be ascertained either from the capacity plan provided for the ship's use1) Where the figures on the capacity plan are given in weight tons (either English or metric), the proper conversion factor should be used for ascertaining the register tons. When the capacities have been obtained from the capacity plan and any doubt arises as to the accuracy of these capacities, the tanks shall be measured as indicated., or as indicated below:
If the length of the tank does not exceed 50 feet or 15.24 metres, three breadths and three heights are taken, but if it exceeds 50 feet or 15.24 metres, the number of breadths and heights to be taken will be five.
The length of each tank is measured between the floors at the ends of the tank. At the points of division of the length and at its ends the heights are then measured at a distance of one-quarter of the tank-top breadth from the middle plane. The breadth is measured at each section where a height has been taken, at the middle of the height. If a tank is of an irregular shape, it should be measured in parts.
All measurements are taken to the shell, the margin plates, and the under side of the tank-top, regardless of stiffeners, or shell and side frames (see Figures 62, 63, 64 and 65).
The cubic capacity of each tank is to be determined in the following way:
The sum of the two end breadths plus four times the middle breadth in the case of three breadths, or the sum of the two end breadths plus four times the even breadths, plus twice the middle breadth in the case of five breadths, is multiplied by one-third of the common interval between the breadths. The area so obtained is multiplied by the mean height (i.e., the arithmetic mean of the various heights measured), and 95 per cent of this last product gives the cubic capacity of the tank in cubic feet or in cubic metres. The capacity in register tons is obtained by dividing the number of cubic feet by 100 or by multiplying the number of cubic metres by 0.353.
The cubic capacity in register tons or in cubic metres of each double-bottom tank or each separate compartment of the double bottom should be noted on the tonnage certificate.
The cubic capacity of any space in a double bottom not available for the carriage of water ballast, stores, fuel oil or cargo should not be included in the cubic capacity of the double-bottom tanks.