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Operability Index – Aft Ramp
If we divide the region of operability (green area) to the total area of the polar chart, we can get a single number that designates the overall operability of the ship, we call this the operability index.
This index is summarized here for the aft ramp versus the ramp’s height from the calm waterline, and for different sea states.
We can see that the operability index is acceptable even for high speed states and throughout the 0 to 30 knots speed range.