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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 HEIGHT AT POINT
(Requires GHS version 19.14 or later ) |
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To check whether a vessel is operating within the limits imposed by
stability regulations, GHS evaluates the righting-arm curve. Some
regulations also make requirements about the height of a point
of interest relative to the waterline. That doesn't have much to do
with the righting arm curve, but it is convenient to have RAH /LIM
make a complete assessment.
The FLOODHT limit type has been around for a long time, but it only considers normal downflooding points or the combination of a specific range of downflooding and weathertight points. A new limit type, HEIGHT AT POINT, requires that a range of points (including points that are unrelated to flooding) be either above or below a specified distance from the waterline. Unlike most limits, HEIGHT AT POINT can be used with both greater-than or less-than symbols. Only one of each may be used at a time in a set of LIMITS. |
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LIMIT (1) HEIGHT AT POINT [n1 [TO n2]] > minheight
LIMIT (2) HEIGHT AT POINT [n1 [TO n2]] < maxheight |
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Because the HEIGHT AT POINT limit works on /NOFLOOD points, it can used in RAH or MAXVCG commands without affecting other limits that use the angle keyword FLD. So now, it is possible to add a bottom immersion requirement to an existing crane stability limit set. Previously, bottom immersion could only be checked with a macro. Another potential use case for this limit is checking the freeboard at a particular location on the vessel. For example, for ships engaged in anchor handling, the IMO requires a minimum freeboard at the stern of one-half of a percent of the ship length (0.005*L). Can you think of other uses? |
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Questions, comments, or requests?
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