Now I know this may seem a silly question for all you experts out there, but for us beginners, can someone please explain the difference between the Gross Registered Tonnage and the Deadweigh Tonnage?
Especially when I see that some ships have a higher DWT than GRT and other vessels have the opposite.
Many thanks in advance,
Scott
Sorry for the continuous questions, but it may help keeping you experts on your toes and keeping the site alive and running :-)
Hi Scott,
Regards to your question about tonnages, gross and net tonnages (GRT and NRT in pre-ITC days, and now GT and NT) are expressions of cubic volume.
Deadweight (DWT)and displacement are expressions of physical weight.
Traditionally, GRT was a calculation of the number of 100 cubic foot 'boxes' a ship could accommodate in its enclosed space. NRT reflected the same figure, but just for the money earning spaces. Now the figure is based around cubic metres and is adjusted with a sliding figure to bring it more into line with the tonnages it was replacing.
Deadweight is how much the ship can carry, while displacement is how much water the ship has to move out of the way.
Tankers and bulk carriers will, more or less, have DWTs roughly two-thirds to double the GT. A container ship will have a DWT in close proximity to its GT, while passenger ships, gas carriers, and car carriers will have quite small DWTs compared to their GT.
To understand this a bit better, a cruise ship has lots of enclosed space. But the weight of the people it carries - even if they've overdone it on the buffet each day - isn't great.
A tanker of equivalent GT on the other hand, is full of oil and this weights a lot more.
Hope this helps.
Steve.
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