The definite assumptions referred to in Regulation II relate to the permeabilities of the space below the margin line.
In determining the floodable length, a uniform average permeability shall be used throughout the whole length of each of the following portions of the ship below the margin line:—
the machinery space as defined in Regulation I (8);
the portion forward of the machinery space; and
the portion abaft the machinery space.
For steamships the uniform average permeability throughout the machinery space shall be determined from the formula—
where
a =volume of the passenger spaces, as defined in Regulation I (9), which are situated below the margin line within the limits of the machinery space.
c =volume of between deck spaces below the margin line within the limits of the machinery space which are appropriated to cargo, coal or stores.
v =whole volume of the machinery space below the margin line.
For ships propelled by internal combustion engines, the uniform average permeability shall be taken as 5 greater than that given by the above formula.
Where it is shown to the satisfaction of the Administration that the average permeability, as determined by detail calculation, is less than that given by the formula, the calculated value may be substituted. For the purposes of such calculation, the permeabilities of passenger spaces, as defined in Regulation I (9), shall be taken as 95, that of all cargo, coal and store spaces as 60, and that of double bottom, oil fuel and other tanks at such values as may be approved in each case by the Administration.
The uniform average permeability throughout the portion of the ship before (or abaft) the machinery space shall be determined from the formula—
where
a =volume of the passenger spaces, as defined in Regulation I (9), which are situated below the margin line, before (or abaft) the machinery space, and
v =whole volume of the portion of the ship below the margin line before (or abaft) the machinery space.
If a between deck compartment between two watertight transverse bulkheads contains any passenger or crew space, the whole of that compartment, less any space completely enclosed within permanent steel bulkheads and appropriated to other purposes, shall be regarded as passenger space. If, however, the passenger or crew space in question is completely enclosed within permanent steel bulkheads, only the space so enclosed need be considered as passenger space.