Question:

I am having difficulty applying GHS limit statements to section 2 of CFR 46 Part 172 Subpart D special Rules Pertaining to a vessel that carries a cargo regulated under 33 CFR Part 157 which states the following.

172.065

Section G

(2) Heel Angle. The maximum angle of heel must not exceed 25 degrees, except that this angle may be increased to 30 degrees if no deck edge immersion occurs.

Answer:

You can look at the problem as follows. There are two LIMITS that apply but you only have to pass one of them. They are,

LIMIT ANGLE FROM EQU TO ABS 25 > 0
LIMIT ANGLE FROM EQU TO DI OR ABS 30 >0

Since we need to pass only one of them, we need to know which is less stringent. To determine this, you can make an initial run using them both. Then, by looking at the results, you can select the one to use in the final run. If you are running a given condition, you could leave them both in as long as the reader understands that only one of them has to pass.

This approach does not necessarily give optimal results in a MAXVCG run since over the range of drafts/trims there is no guarantee that the same one will always be the less stringent. However in practice it seems to work out that either another limit is controlling or the same one of these is controlling.

You could go further, and set up your run file to look at the system variable FREEBD and on that basis select the appropriate limit. This would work for a given condition where the VCG is known. For example,

MACRO LIMA
LIMIT(1) ANGLE FROM EQU TO ABS 25 > 0
/
MACRO LIMB
LIMIT(1) ANGLE FROM EQU TO DI OR ABS 30 >0
/
SOLVE
IF {FREEBD} > 0 THEN .LIMB ELSE .LIMA
HEEL *
HEEL = 0
RA /LIM