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

(Requires GHS version 16.34 or later with SK)

SEAKEEPING has come a long way since it was first introduced in January of 2018. And with more users adopting the new capabilities, continual development has been shaped by user input. Along with a 'thank you' to all of our SK users and critics, we are pleased to announce the release of a major mid-year update to this module. We've got some pretty exciting things to share with you.

Since there are far too many new features to announce in a single COW, we thought it best to start with one of the more visually compelling features of the new release. We can understand that ship motions might not be the most exciting thing on a Tuesday afternoon, but when you create a yaw plot that looks like a four-leaf clover, somehow people start to take notice.

Love them or hate them, polar plots are common in ship motions, and, if asked, the SEA command will now automatically generate these plots. This automation is made possible by an extension to the /HEADING parameter, in which multiple headings (or a range of headings) may be specified within a single parameter. That's right, no more macro loops (although we still love macro loops, and you should too).

The new syntax is simple, and looks something like this:

CRT (1) "FOREDECK" 86.939f,0,11.9
CRT (2) "MAIN DK S" 28.350f,7.859s,9.4
CRT (3) "BRIDGE" 12.6f,0,20.4


SEA /HEAD:0,15,...,360 /MSI:CRT /POLAR:RMS,MSI /CRT:1,2,3

The /POLAR parameter lets you specify any type of response statistic, or derived response, to be plotted using identifiers. And you can create polar plots of more than one type of output simultaneously. In the above example, we are plotting RMS values as well as Motion Sickness Incidence (see COW103 for more about MSI). /POLAR always creates a plot for each mode (Surge, Sway, Heave, Roll, Pitch, and Yaw) but only the Sway RMS Acceleration plot is shown below. MSI is a derived response (derived from the vertical motions), so it is only a single plot, as shown.

If you run multiple speeds, you will get a polar plot for each speed. You can control the range and density of the data being plotted by adjusting the interval between successive headings, or by adjusting the heading range. If you have a vessel or loading condition that ensures port-starboard symmetry, and you aren't evaluating off-centerline Critical Points, it is reasonable to run only headings between 0 and 180 degrees to reduce computation time.

Those who watch the release notes carefully may have noticed that polar plotting was actually added to ME PLOTSTART back in version 16.28. This means you now have all the tools necessary to create any polar plot within GHS.

Questions, comments, or requests?
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