ShipSpotting.com
Login: Lost Password? SIGN UP
Ship Photo Search
Advanced Search
Pages: [1]
  Print  
Author Topic: What's the Difference between Gross Tonnage and Dead Weight Tonnage?  (Read 54310 times)
0 Members and 1 Guest are viewing this topic.
Cody Williams
Webmaster
Top Poster
*****
Offline Offline

Posts: 1,114



View Profile WWW
« on: December 30, 2009, 08:16:42 pm »

Does anyone known What the Difference between Gross Tonnage and Dead Weight Tonnage? I've googled it but I'm getting all sorts of answers.

Kind Regards,

Cody
Report to moderator   Logged

I can be contacted at cody@shipspotting.com
Bob Scott
Guest
« Reply #1 on: December 30, 2009, 08:32:22 pm »

Gross tonnage is a volumetric measurement of the enclosed space in a ship. It has NOTHING to do with weight. The unit used is the gross TON.

Deadweight tonnage is the WEIGHT in metric TONNES (1,000 kg) of cargo, fuel and stores that will put the ship down to its loadline marks.
Report to moderator   Logged
Morten
Home away from home
****
Offline Offline

Posts: 301


View Profile
« Reply #2 on: December 30, 2009, 10:12:35 pm »

Actually, to be strictly correct, Gross tonnage is just an index and do not carry any unit. It's not really usable for anything in real life unless you hold a certificate as an officer for smaller ships, in which case 3000 GT is interesting. Other than that, it is something used by governing bodies to determine manning requirements and other boring stuff. Other than that, it is used by classification companies, P&Is, ports etc. to determine fees.
It is often used to compare the size of ships, though it is as useless for comparing ships as TEUs or LOA. I.e. a 300 m VLCC will have a far larger GT than the Oasis of the Seas - despite the Oasis being both longer and wider...

Same sort of goes to DWT. It isn't really a usable measure for anything that can be of interest to anyone except the shipowners and flag and port states.

Aside from that, what "BobS" said!
Report to moderator   Logged
John Jones
Top Poster
*****
Offline Offline

Posts: 4,600



View Profile
« Reply #3 on: December 30, 2009, 11:58:24 pm »

Cody,

The word ton with regard to a ship has many different meanings and ways of being calculated.

The word 'ton' does not refer to a weight ton at all. It was originally derived from the word 'tun' and referred to the 252-gallon barrel used in the wine trade in the days of sail. Then a convenient way of estimating a ship's size was to calculate how many of these barrels she could carry and that figure was used as the ship's 'register tonnage.'

From that tradition there evolved 'Gross Register Tonnage' (GRT) and 'Nett Register Tonnage' (NRT). These were a measure of the enclosed space in the ship calculated on the basis of a ton being 100 cubic feet. 'Gross' being the total space, while 'Nett' was the total space less that used for machinery and accommodation.

There tended to be variations from country to country in the method of measuring ships for their GRT and NRT so a new system of measurement was internationally agreed and came into full force in 1994. The size of the 'ton' now varies between 95 and 105 cubic feet depending on the size and type of the vessel. To differentiate between the old and the new system the word 'registered' was dropped so that we now have Gross Tonnage (GT) and Nett Tonnage (NT).

Despite world-wide discussion and agreement, the Suez Canal and the Panama Canal authorities decided to retain their unique methods of measuring ships for the purpose of calculating canal charges.

Deadweight is the difference in tons between the light and loaded displacement but its commercial importance is that it represents the total weight a ship can carry which includes cargo, fuel, stores, freshwater etc. DWAT stands for deadweight all told.

More important to those concerned with the ship commercially are the initials DWCC standing for deadweight cargo capacity. This indicates the potential earning capacity of a ship. It assumes that the maximum quantity of stores and bunkers are onboard. In practice the operator may increase the DWCC by carrying less bunkers.

Hope this is of interest.

Regards
John J.
Report to moderator   Logged

Any views expressed in the forum are my own personal opinions and are not to be taken as those of members of the admin team or of the site owners.
Bob Scott
Guest
« Reply #4 on: December 31, 2009, 12:56:34 am »

Hi, Cody,
I have here a book called "The Tonnage Measurement of Ships". It runs to over 100 pages (plus indices and appendices) and only covers gross and net tonnages, with not a word about deadweight!
How complicated do you want to get: because this can become a really complicated subject?
In my initial post, I tried to sum it all up in just two sentences but Blue Wombat and John Jones have added a good bit of meat to what I said.
John's last two paragraphs contain the meat that I was tempted to add . . . but didn't, in the interests of simplicity.
If you want to know how much coal,ore or grain, etc you can pour into a bulker's holds or how much liquid into a tanker's tanks, you do need to know the ship's cargo deadweight (DWCC). Pour in too little and the owner will lose money; too much and the ship might even sink!
For the ship spotter, gross tonnage is about the best guide you will get to how 'big' a ship is compared to others but, as Blue Wombat says, it is not a lot of help when comparing a cruise liner with a VLCC.
Having worked in the shipping industry, I find it difficult to compare bulker with bulker or tanker with tanker in terms other than deadweight tonnage. Similarly I find it hard to think of a containership in measurements other than TEU.
What I do find, though, is that I get very irritated when some non-specialised, journalist person refers to a ship as WEIGHING x-thousand tons, when they are quoting the ship's gross tonnage!
Hope you are now a much wiser shipspotter. I have always reckoned that the more you know about how the industry works, the more interesting it becomes as a hobby interest.
Cheers
Bob Scott
Report to moderator   Logged
John Jones
Top Poster
*****
Offline Offline

Posts: 4,600



View Profile
« Reply #5 on: December 31, 2009, 01:31:54 am »

Cody,

Bob is absolutely right when he says this can become a really complicated subject. We've not even mentioned compensated gross tonnage yet :-)

In the industry different ship's tend to be measured by different parameters according to the ship type. Be it deadweight, pax, cubic metre capacity, TEU intake, lane metres or whatever.

But to sum up, in general I think we ship spotters probably find gross tonnage a useful measurement of a ship, as in 'there's a big one coming in', due to the fact that it is a volumetric measurement and gives a fair indication of the ship's actual physical size.

Regards
John J.
Report to moderator   Logged

Any views expressed in the forum are my own personal opinions and are not to be taken as those of members of the admin team or of the site owners.
Bob Scott
Guest
« Reply #6 on: December 31, 2009, 11:59:13 am »

Ken,
I hope that “speaking as an admin” you are not implying that deadweight tonnage should not be mentioned or discussed on the site. As I read it, Cody was merely asking a straightforward question about the difference between gross and deadweight tonnages – nothing to do with site standards.
It is refreshing to have one of our younger members seeking to add some technical knowledge to his hobby interest in ships and the shipping industry . . . rather than just trying to amass millions of photos of ships without knowing or wanting to know anything about them.
It is also refreshing to have a thread on the forum that is not whingeing about the site or copyright issues.
Bob
Report to moderator   Logged
Bob Scott
Guest
« Reply #7 on: December 31, 2009, 05:09:08 pm »

Ken,
Me start an argument?
Never!!

Happy Hogmanay!
Bob
Report to moderator   Logged
holedrille
Just can't stay away
***
Offline Offline

Posts: 118


View Profile
« Reply #8 on: January 01, 2010, 04:45:44 pm »

Is there yet another measure, DWLT, which I presume stands for Deadweight Light Ton. It seems to be used in reporting value of a scrapped ship, so could indicate the weight of steel  (and asbestos , paint,  glass and plastic?) in the hull. Current selling prices range from 300 to 400 US$ per DWLT, more if there is much stainless in the hull.
David
Report to moderator   Logged
Guest
Guest
« Reply #9 on: January 01, 2010, 08:56:28 pm »

Quote

holedrille wrote:
Is there yet another measure, DWLT, which I presume stands for Deadweight Light Ton. It seems to be used in reporting value of a scrapped ship, so could indicate the weight of steel  (and asbestos , paint,  glass and plastic?) in the hull. Current selling prices range from 300 to 400 US$ per DWLT, more if there is much stainless in the hull.
David


Hi David

I get the 'joke' - there is a Black and Decker Drill model called a  DWLT and that ties in with your nickname/user name.

Regards
Report to moderator   Logged
David Ford
Home away from home
****
Offline Offline

Posts: 285


View Profile
« Reply #10 on: January 02, 2010, 09:07:05 am »

David

I seem to recall that the abbreviation used in respect of ships to be scrapped is LDT, which stands for Light Displacement Tons. A ship scrapper is only interested in the weight of steel, copper etc that he is going to be able to recover and sell. So the displacement tonnage of the ship [i.e. the weight of water that it displaces when afloat] is a reasonably accurate measure of the weight of ship that he will break up. The 'light' refers to the fact that the ship will have no cargo on board when delivered to the breaker - i.e. she will be 'light'.

David Ford
Report to moderator   Logged
Pages: [1]
  Print  
 
Jump to:  


Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC
Page created in 0.048 seconds with 19 queries.
Copyright © 2010 All rights reserved