Minggu, 03 Maret 2013

Ship's Gross Tonnage (GT) what does it supposed to means? and what does it relate to DWT?

By Agung Aang on Monday, March 4th, 2013, 01.00 AM

It's all started with a simple humble curiosity question raised by my Boss, that's indeed managed to put me in the corner as I was unable to give a simple clear enlightening answers that managed to answer his question once and for all.

Soon it's successfully turned became my personal curiosity instead, after so many years back. What does ship's Gross Tonnage (GT) supposed to means? In accordance to the International Trade Tonnage Convention on Tonnage measurement 1969, the definition of GT, formerly known (before ITTC 1969) as Gross Register Tonnage (GRT) and after 1994 the term was totally replaced with GT, is the measurement of total internal volumetric space of the ships covering all the enclosed and convined space the ship has onboard.

How its calculated? it's simply as the factor of Ship's volume i.e. GT = K x V , where V is volume in CBM, whilst K is a figure valued from 0.22 - 0.32 (depending on the ship's size) defined as K = 0.2 + (0.02 Log10 x V), thus means in order to get Tonnage measurement over the GT, the ship's space in volumetric (CBM) shall be multiplied by certain density in the value of 0.22 up to 0.32.

In an empirical way, GT could also be simply calculated by formula of
GT (in T) = L x B x D (all in Ft)
                       125

Whereby L is vessel's length in M, B is vessel's breadth in M, and D is vessel's depth also in M

Another term very much related to this GT is NT (Nett Tonnage), it's defined as the Total internal volume / space in CBM after deducted with some several non-freight / non-comercial compartment spaces onboard the ship such as wheel-house, crew's accommodation, kitchen & lavatory, double bottom tank for ballast, etc.

One shall not confuse these GT & NT with other terms as DWT, LWT and Displacement, as these measurement units are due for the weight measurement of the ships, where the density value normally applied here is the density of the sea water i.e. 1.025 Kg/m3, whilst GT & NT are the terms used to measure the volume over the ship's compartment onboard.

Thus again it does not have direct relation to the DWT & LWT, but to mention it's merely the volumetric measurement over the ship's space.

Hopes it's satisfy everyone curiosity.