Question:

If you have a vessel with water in the engine room bilge, GHS will allow for that water to be considered provided the ER is modeled as a tank. Now you decide to conduct an inclining experiment without emptying the bilge water (say it is the realistic normal operating condition for the vessel...).

The data shown in the inclining run provides a total weight and a VCG that is affected by the movement of the bilge water port and stbd. Is it possible to use the total weight and VCG in GHS "STatus" to attempt, by trial and error using the GHS model with the bilge water, to search (by entering as input) for the lightship weight and VCG?

It appears that the VCG for the lightship will have to be entered with an higher value than the real VCG? I don't see in "STatus" that GHS did account for the surface effect of the bilge water (which would have translated in a rise in VCG to that measured during the stability test)? Some thoughts other than "never conduct a stability test with liquid in the bilge" please.

Answer

You can have bilge water as well as any other tank loading and other miscellaneous weights aboard. Getting the light ship is easy -- no trial-and-error required. Here are the steps.

ADD "Inclining weights" w, l, t, v
HEEL = x `sets the list observed with the inclining weights as above
DRAFT = d1 @ l1, d2 @ l2, etc. `sets the observed drafts (av p&s)
LOAD (bilgetank) = x
LOAD ...
ADD ... `weight not to be included in light ship
GMTMMT = x `GM moment (slope of inclining wt moment vs heel)
\As-inclined condition\
STATUS WEIGHT, DISPL, WPL
LOAD (*) 0
DELETE "Inclining weights"
DELETE ...
ADD ... `light ship weights not aboard during inclining
WEIGHT * `Combines all remaining added weights into light ship
SOLVE
\Light-ship condition\
STATUS GHS

The STATUS WPL category will show the free-surface contributions.

The only problem with having bilge water and other weights aboard during an inclining is knowing exactly what they are. In other words, you need to be sure the model corresponds to the real ship. That means you need an accurate model of the bilge and an accurate sounding. Likewise for any other tank loads. Non-lightship dry (fixed) weights must also be accruately represented in the model. It's your decision as to whether it's easier to remove such things from the vessel or to model them in GHS. Copyright (C) 2005 Creative Systems, Inc.