USCG Exam Practice · Vessel stability — metacentric height, free surface
When calculating free surface effects for stability purposes under 46 CFR Part 28, how must tanks fitted with cross-connection piping be treated?
- AEach tank must be calculated individually at its actual fill level
- BThe tanks must be assumed to be one common tank unless isolating valves are installed and kept closed✓ correct
- CCross-connected tanks are exempt from free surface calculations if total volume is less than 5 percent of displacement
- DThe tank with the smaller free surface effect is used for the calculation
Why B is correct
46 CFR §28.540(b) states that the free surface effect of tanks fitted with cross-connection piping must be calculated assuming the tanks are one common tank, unless valves that will be kept closed to prevent transfer of liquids as the vessel heels are installed in the piping.
Cited:46 CFR §28.540
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