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General HydroStatics
Ship Stability Software |
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Command of the Week
(New or interesting aspects of GHS that you may not know about) |
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LIMIT FREEBOARD
(Requires GHS version 19.14 or later ) |
| GHS is a living application and therefore undergoes continuous improvement. For example, a few weeks ago, a new LIMIT type was added. It was reported in the change notes as: |
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Version 19.14 - LIMIT FREEBD[0] [AT EQU|EQU0] > freeboard was added to limit the lowest deck-edge freeboard above waterplane (ignoring margins if FREEBD0 is used) at equilibrium (disregarding external moments if EQU0 is used). |
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LIMIT FREEBD does what you would probably expect: evaluate the vessel's freeboard. Some of you might be thinking, "Didn't you recently add system variables to report the minimum freeboard locations." That is true! In Version 18.62A, FBLOC and FB0LOC system variables were added to return longitudinal locations of minimum freeboard FREEBD and FREEBD0, respectively with and without margins. STATUS FREEBOARD has long been available to add freeboard values to reports, and system variables can include minimum freeboards in NOTES or to files. But now, freeboard limits can be used in MAXVCG calculations also. |
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| The syntax diagram in the version notes above indicates that there are four possible permutations of this new limit, although only one can be used at a time in a set of LIMITS. |
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LIMIT (1) FREEBD AT EQU > 1
LIMIT (2) FREEBD0 AT EQU > 1 LIMIT (3) FREEBD AT EQU0 > 1 LIMIT (4) FREEBD0 AT EQU0 > 1 |
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The FREEBD limit type reports the freeboard respecting any component margins, whereas the FREEBD0 limit type ignores margin distances. The angle EQU respects the heeling moments, whereas EQU0 ignores heeling moment. If there isn't a heeling moment present, then both angle keywords produce identical results. Like limits that involve the angle of deck immersion (DI), the geometry file must contain deck edge marks.
Below is a sample report showing STATUS FREEBOARD followed by RAH with a freeboard limit. Note that the attained value matches the freeboard to the margin line in the STATUS output. The location of the smallest freeboard value is given in the limit description in the RAH output. |
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| If you have a feature that you'd like to see added to GHS, please send us a message at support@ghsport.com. |
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Questions, comments, or requests?
Contact Creative Systems, Inc. USA phone: 360-385-6212 Fax: 360-385-6213 Office hours: 7:00 am - 4:00 pm Pacific Time, Monday - Friday Mailing address: PO Box 1910 Port Townsend, WA 98368 USA Click here for an index to this and previous COWs |