9.5 Tank Overflows
9.5.1 General Requirements
Generally, all tanks capable of being filled by a pumping system, as indicated in 4-6-4/9.1.2, are to be provided with a means of overflow. This may be achieved by overflowing through dedicated overflow pipes or through the tank vents, provided the size of the vents meet 4-6-4/9.3.3(b). Overflows are to discharge outboard, i.e., on the weather deck or overboard, or into designated overflow tanks. Overflow lines are to be self-draining.
9.5.2 Overflow Pipe Size
In general, the aggregate area of the overflow pipes is not to be less than 125% of the effective area of the filling line. Where high capacity or high head pumps are used, calculations demonstrating the adequacy of the overflow as well as the vent to prevent over- or underpressurization of the ballast tanks are to be submitted. See also 4-6-4/9.3.3(b). Where overflows complying with this requirement are fitted, tank vents need only meet the minimum size complying with 4-6-4/9.3.3(a). Where, however, tank vents complying with 4-6-4/9.3.3(b) are fitted, separate overflows will not be required.