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

(Requires GHS version 16.20B or later with SK)

A statistical estimate of deck immersion due to motions, or "shipping water", is sometimes needed when developing operability criteria for a vessel in a seaway. It may also be a factor when deterministically selecting a freeboard. This information can prove to be a helpful consideration early in the design process.

The ever-expanding SEAKEEPING command is now able to perform this type of analysis. The parameter /SHW computes the probability and frequency of occurrence of deck immersion for any single point, or all seakeeping critical points, on the vessel.

In the frequency domain, shipping water events are computed from the variance of the relative vertical motions and the point freeboard. Sure, SEAKEEPING already computes relative motions, the point height can be found via HEIGHT, and the variance (m0) is given in the statistics tables, but /SHW just makes things much easier. Take the following example:

 SEA /HEAD:180 /SPEED:6.3 /CRT:1,2,3,4 /TIME:8 /SHW:CRT

In this example, deck immersion will be computed for critical points (1) through (4), as indicated by the /CRT parameter. The number of occurrences over an 8 hour interval will also be given, thanks to the /TIME parameter. A "Shipping Water" section is then automatically added to the end of the seakeeping report, before any summary tables:

Computing deck immersion statistics for a number of headings and speeds is then simply accomplished using a macro loop.

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