Calculations - Hydrostatics Form
- Last UpdatedDec 17, 2025
- 5 minute read
In order to produce the hydrostatic particulars, you can select the Form Calculations - Hydrostatics icon in the Application Tree and ensure that all input data is complete and current. If a user has any suitable data he can input an estimated value of the midship hull girder still water vertical hogging or sagging bending deflection. Hydrostatic particulars can be calculated for the mainhull (including appendages, if defined) for either moulded or extreme drafts, for a range of drafts, and for a single combined trim and heel condition. The results are then presented in both tabular and graphical form.
The particulars that are calculated are as follows:
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Displacement.
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Tonnes per centimeter/tons per inch immersion.
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Moment to change trim one centimeter/inch.
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Height of transverse metacenter above baseline.
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Longitudinal center of buoyancy.
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Longitudinal center of flotation.
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Height of longitudinal metacenter above keel.
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Wetted surface area.
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Transverse center of buoyancy.
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Waterplane area.
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Vertical center of buoyancy.
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Longitudinal metacentric radius.
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Transverse metacentric radius.
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Block coefficient.
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Maximum sectional area coefficient.
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Prismatic coefficient.
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Waterplane area coefficient.
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Transverse centre of flotation.
The following gives a list of the terminology and units used for both the hydrostatics and the deadweight scale (see Deadweight Scale). The LBP is the perpendicular distance between the AP and FP.
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DRAFT |
The moulded draft at midships (LBP/2). |
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Measured normal to the moulded baseline. |
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Units of meters or Feet. |
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DISPLT |
The displacement of the ship in water of the specified density. The default density is: |
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= 1.025 tonne/m3 |
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If no shell thickness is specified then DISPLT is the moulded displacement of the main hull and appendages. If an average shell thickness is specified then this DISPLT is the extreme displacement that means, moulded displacement plus the displacement of the shell plating. |
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The displacement of the shell plating is calculated from the shell thickness and the wetted surface area of the moulded shape. The wetted surface area estimation is detailed below, see WSA. |
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Units of Tonnes or Tons. |
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TPC/TPI |
The tonnes per centimeter immersion or the tons per inch immersion. |
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WPA is the moulded waterplane area including appendages but not including shell plating. WPA is defined below. |
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Units of Tonnes or Tons. |
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MCTC/MCTI |
The moment to change trim one centimeter or one inch between the perpendiculars. |
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For simplicity, MCT is assumed to be independent of the VCG, that means, BML replaces GML in the formula, as given below: |
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BML is defined below. |
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Units of Tonnes-meters or Tons-Feet. |
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LCB |
The longitudinal centre of buoyancy of the moulded hull volume, that means, including appendages and excluding shell plating. Measured from the AP, positive forwards and parallel to the baseline. |
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Units of meters or Feet. |
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LCF |
The longitudinal center of flotation of the moulded waterplane area, that means, including appendages and excluding shell plating. Measured from the AP, positive forwards and parallel to the baseline. |
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Units of meters or Feet. |
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TCF |
The transverse center of flotation of the moulded waterplane area, that means, including appendages and excluding shell plating. Measured normal to the centreline, positive to starboard. |
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Units of meters or Feet. |
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KML |
The height of the longitudinal metacentre above the moulded baseline at midships. The moulded hull waterplane area and volume are used, that means, including appendages but not the shell plating. |
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Units of meters or Feet. |
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WPA |
The moulded waterplane area including appendages and excluding shell plating. |
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Units of meters2 or Feet2. |
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VCB |
The vertical center of buoyancy of the moulded hull volume, including appendages and excluding shell plating. Measured normal to the moulded baseline at midships. |
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Units of meters or Feet. |
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TCB |
The transverse center of buoyancy of the moulded hull volume, including appendages and excluding shell plating. Measured normal to the centerline, positive to starboard. |
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Units of meters or Feet. |
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BML |
The longitudinal metacentric radius, that means, the height of the longitudinal metacenter above the center of buoyancy for the moulded hull. |
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Units of meters or Feet. |
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BMT |
The transverse metacentric radius, that means, the height of the transverse metacenter above the center of buoyancy for the moulded hull. |
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Units of meters or Feet. |
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CB |
The block coefficient: |
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Moulded Volume includes appendages and excludes shell plating. |
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CM |
The midship sectional area coefficient: |
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Midship Sectional Area is the moulded section. |
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CW |
The waterplane area coefficient: |
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CP |
The prismatic coefficient: |
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KMT |
The height of the transverse metacenter above the moulded baseline. The moulded hull waterplane area and volume are used that means, including appendages and excluding the shell plating. |
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Units of meters or Feet. |
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WSA |
The wetted surface area can be calculated in one of two ways (as specified at SETUP/OPTIONS): |
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1) |
Directly from the geometry model, or |
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2) |
Estimated using the Denny-Mumford formula: (1.7*LBP*DRAFT + (Moulded Volume)/DRAFT)*CF, where CF = User defined correction factor. |
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Units of meters2 or Feet2. |
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