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Stability & CargoPage 8 of 12

The cargo figure: from the ullage totals to weight in air

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Cargo weight in air: free water out, VCF to 15 °C, then the density less 0.0011Total Observed Volume 121540 m³, less 640 m³ of free water = Gross Observed Volume 120900 m³; × VCF 0.9738 = Gross Standard Volume 117732.4 m³. The density at 15 °C in vacuo is 0.8712; less the air buoyancy correction, 0.0011 t/m³, the weight correction factor (WCF) is 0.8701. Weight in air = 117732.4 × 0.8701 = 102439 t; the same volume in vacuo would be 102568 t, which is not the cargo figure.TOVGOVGSV121540 m³120900 m³117732.4 m³− free water 640 m³× VCF 0.9738 (to 15 °C)× WCF 0.8701weight in air 102439 tDENSITY AT 15 °C · T/M³ (MAGNIFIED)0.86950.87000.87050.87100.8715in vacuo 0.8712in air 0.8701− 0.0011 air buoyancyin vacuo 102568 t — not the cargo figureVolumes to one true scale from zero · density scale magnified

The rule

  • GOV = TOV − free water: the water under the oil is measured and taken out before anything else.
  • GSV = GOV × VCF: the volume correction factor for the observed temperature brings the oil to 15 °C, the temperature its density is quoted at.
  • GSV × density at 15 °C is the weight in vacuum (in vacuo). Oil weighed in air is held up slightly, so take the air buoyancy correction, 0.0011 t/m³, off the density at 15 °C first: that gives the weight correction factor (WCF).
  • Weight in air = GSV × WCF. The in-vacuo figure is heavier, and it is not the one ship and terminal compare.

Formula

  • GSV = (TOV − free water) × VCF
  • WCF = density at 15 °C − air buoyancy correction
  • Weight in air = GSV × WCF

Worked example

Total Observed Volume121540 m³
Free water measured640 m³
Volume Correction Factor at the observed temperature0.9738
Density at 15 °C in vacuo0.8712 t/m³
  1. GOV = 121540 − 640 = 120900 m³
  2. GSV = 120900 × 0.9738 = 117732.4 m³
  3. WCF = 0.8712 − 0.0011 = 0.8701 t/m³
  4. Weight in air = 117732.4 × 0.8701 = 102439 t

Answer102439 t

Common mistake

Multiplying the GSV by the density at 15 °C as it stands: 117732.4 × 0.8712 = 102568 t.

That is the weight in vacuo. Ship and terminal compare the weight in air, 129 t less here — 0.0011 is small for one cubic metre and large for a whole parcel.