General HydroStatics Ship Stability Software

Command of the Week (New or interesting aspects of GHS that you may not know about)

VCF (review) (Requires GHS version 17.06A or later)

The Center of Flotation is the centroid of a ship's waterplane area, the point through which the axis of rotation passes when inclining a free-floating ship in any direction. The Longitudinal and Transverse Center of Flotation coordinates are available via LCF and TCF system variables, as well as appearing on STATUS WPL, GHS, and COMPONENT /FORM reports. The VCF, which is the Vertical Center of Flotation in the ship's 3-D coordinate system, is provided as well by none other than the VCF system variable. VCF values are also reported using the STATUS WPL /VCF parameter, as shown here:

Notice how WPA, LCF, TCF, and VCF are shown for HULL, as might be expected. Notice too how they are also shown for flooded tanks, which act as effective deductions from the buoyant HULL waterplane area. All these buoyant factors are accounted for in the "Total Waterplane" line, which shows their net effective waterplane area and Center of Flotation. These are the same total values returned by the WPA, LCF, TCF, and VCF system variables. But what if you don't care about these net effective values, but instead want the HULL waterplane area and its centroid location? That's available using the counterpart TWPA, TLCF, TTCF, and TVCF system variables. Just select HULL as the current PART, then you can harvest these waterplane values directly:

PART HULL ME {PNAME} WPA = {TWPA} LCF = {TLCF} TCF = {TTCF} VCF = {TVCF}

A cool use for these system variables is to define Critical Points at CF locations to visualize waterplane centers in Condition Graphics slices. For example:

READ FV /QUIET | DRAFT 8 | SOLVE WEIGHT LCG TANK HOLD2.C | TYPE FROZEN HEEL 15 | TRIM 10 | LOAD 25% | SOLVE CRTPT (1) WPLCF {LCF} {TCF} {VCF} CRTPT (2) HOLDCF {TLCF} {TTCF} {TVCF} DI STATUS PROFILE:BE,PLAN:BE,BODY@{TENDA}@{TLCF}@{TENDF}@{LCF}

That pops up this illuminating display:

Questions, comments, or requests? Contact Creative Systems, Inc. support@ghsport.com USA phone: 360-385-6212 Fax: 360-385-6213 Office hours: 7:00 am - 4:00 pm Pacific Time, Monday - Friday Mailing address: PO Box 1910 Port Townsend, WA 98368 USA www.ghsport.com Click here for an index to this and previous COWs