Tonnage Calculation (Gross & Net Tonnage)

Gross Tonnage image

1. Gross Tonnage
This is a function of the volume of all ship's enclosed space (from keel to funnel) measured to the outside of the hull framing.

Then the Gross Tonnage can be obtained with following formula :
                            
         Gross Tonnage (GT) = k1.V
        
Where :
             k1 factor  = 0.2 + 0.02*Log10(V)
                               (0.22 up to 0.32, depending size of the ship)
             V (m3)     = Volume displacement

2. Net Tonnage
This is based on a calculation of the volume of all cargo spaces of the ship. It's indicates a vessel's earning space and is a function of the moulded volume of all cargo spaces of the ship.

 Net Tonnage image

Therefore the Net Tonnage can be obtained with following formula :

Net Tonnage (NT) = Max. of B + k3*(N1+N2/10) or (abt. 0.3*GT)

 Where :
              B    = Max. k2*VC*A or 0.25*GT
              k2   = 0.2+0.02Log10(VC)
              VC  = Total volume of cargo spaces (m3)
              k3   = 1.25*(GT+10000)/10000
              A    = min. of ((4*D2)/(3*D1))^2
              N1  = Number passengers in cabin
              N2  = Number passengers other
              D1  = Depth moulded (m)
              D2  = Draft moulded (m)

Please be CONSIDER & REMEMBER !!!

• These are the function of volume. Tonnage = f (volume)
• Tonnage is not the measurement of weight, it's all about volume.
• International Maritime Organization (IMO) regulates the tonnage measurement.
• GRT, NRT, GT and NT are unitless index for indication of volume (capacity) and uses for commercial purposes.
• If you know GT, you can know how big the ship is.
• If you know NT, you will know how many cargoes the ship can carry.  

Hopefully helpfully 😊
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