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

MARGIN (part 2)

There are few more tricks to know about deck edges and margins in GHS.

One scenario that occurs frequently can be demonstrated perfectly with our trusty fishing vessel. Often a step in the main deck is created as a separate component from the hull. In this case the deck edge should be marked on the upper component and on the lower component for only a portion of the length.

So for example, let's say we want to mark the deck edge as shown below, on the focsle, and on the hull aft of 23.1f:

This could be done in Section Editor in just a few minutes. Simply use CTRL+D to add the deck edge to both components and then use CTRL+SHIFT+D to remove DK marking from Hull Stations 1-9. CTRL+SHIFT+D toggles the DK marking on or off for the current point.
To save the deck creation as part of a PM run file, use the following two commands:

 deckedge 23.1f,40.81    `mark component named HULL
 modify hull\focsle.c
  margin 0
This technique is similarly useful when the hull model includes an appendage, such as a swim platform, that shouldn't be considered for deck immersion.
You only really need a few deck edge points to calculate accurate freeboard readings, so if you have a really complicated hull form, consider just adding a few DK marking in SE, inserting new points as necessary. The chine of the fishing vessel is marked at every other station. The STATUS FREEBOARD report will show all deck points that are defined.

The individual deck edge points even appear in the on-screen Condition Graphic.

If you've defined a margin but don't need it for a particular task, you don't have to go back and modify the GF file. Just use the DI0 limit keyword in place of DI, or use the FREEBD0 system variable in place of FREEBD.

Questions, comments, or requests?
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