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


This has to do with the selection of heel angles used in the generation of stability curves. The RAH (Righting Arms in Heel) command takes heel angles as parameters, as in

  RAH 0, 5, ... 60
Alternatively, if the angles list is omitted, the list of angles previously established by the ANGLES command is used. By default that list is zero through sixty at five-degree increments.

One advantage of using the ANGLES command is that the direction of heeling is easily changed. The procedure is as follows:
1. Heel the vessel toward the side which you want the RA curve to proceed;
2. Give the ANGLES command with an asterisk in place of the angles list.
For example,

This generates a righting-arm curve starting at zero heel and proceeding to the port side. Note that the heel angle was returned to zero before the RAH command (commonly abbreviated to RA) was given. The reason is that RA starts at the present heel angle. In other words, the angles in the list are taken as being relative to the initial heel angle.

Therefore, if you want to start at the equilibrium heel angle, the procedure is,

When giving the angles list, the ellipsis notation can appear anywhere after the interval has been established. For example,

  ANGLES 0, 2.5, ..., 30, 35, ..., 60
How would you go about making a single righting-arm curve to cover heeling in both directions? One way would be,

  ANGLES 0, 5, ... 120
As mentioned in the GHS user's manual, the MAXVCG and CC (Cross Curves) commands also make use of ANGLES list. Your bonus for reading to the end of this uninspiring COW is that you can pencil into your manual's ANGLES page the fact that HMMT TANK also uses the ANGLES list.

Questions, comments, or requests?
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