General HydroStatics
Ship Stability Software
Command of the Week
(New or interesting aspects of GHS that you may not know about)

ABSOLUTE RATIO LIMIT

A recent COW featured the Reserve Ratio Limit, so it seemed apropos to highlight a similar limit called the Absolute Ratio. The Absolute Ratio is more general than the Reserve Ratio, the latter being primarily used for US Navy regulations. In fact, the Absolute Ratio finds it way into many different types of stability criteria including MODU intact, towing, and heavy lifting with cranes.

As shown below, the Absolute Ratio is the Absolute Area (AA) divided by the Heeling Area (HA) for a specified angle range. Note that the two area regions overlap. Do you notice any similarity with the Reserve Ratio limit?




Unlike the Reserve Ratio, the angle range in the Absolute Ratio can include regions of negative area. This makes the limit more flexible but also more sensitive to the angle keywords used. It is nearly always correct to include RA0 or RA00 (without moments) as a terminating angle even if it isn't mentioned in the regulation. This also means the limit must be entered twice to cover a set of three terminating angles:
 LIMIT ABSOLUTE RATIO FROM EQU0 TO ABS 40 OR RA0 > 1.4
 LIMIT ABSOLUTE RATIO FROM EQU0 TO FLD or RA0 > 1.4
The syntax diagram shows that the word ABSOLUTE is optional.

Like most COWs about LIMITs, this one doesn't have any margin for jokes.

Questions, comments, or requests?
Contact Creative Systems, Inc.

support@ghsport.com

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