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Discussion Starter · #1 ·
Reading through the various threads I thought it might be useful to provide a few words of explanation on how to measure a vessels tonnage.

DEADWEIGHT: (DWT)

The deadweight is the carrying power of the vessel and is over and above the actual lightweight of a vessel. It is therefore the weight in tons or tonnes (metric) of the cargo, fuel, stores, water, crew, etc which the vessel may carry in safety.

DISPLACEMENT: (D't)

The displacement is the measure of the weight of the vessel plus all outfit and cargo. A displacement "ton" is estimated at 35 cubic foot of sea water or 36 cubic foot of fresh water. It should be noted that this figure will vary according to the draught of the vessel and may be expressed in tons or tonnes.

LIGHTWEIGHT: (LWT)

The lightweight is the measure of the weight of steel, wood, outfit and machinery of the vessel however it does NOT INCLUDE the weight of the oil or water contained in any machinery. The lightweight is usually calculated during the time the inclining experiment is carried out.

GROSS TONNAGE: (GT)

The gross tonnage is the capacity of the spaces found within the frames or ceilings of the hull and of the closed spaces above deck level available for the carriage of cargo, stores, passengers and crew. This is a general description and there are certain exceptions however they are generally expressed in tons of 100 cubic foot per ton.

NET TONNAGE: (NT)

The net tonnage is again calculated as 100 cubic foot per ton and is obtained from the gross tonnage figure by deducting the space taken for the accommodation allocated to the Master, Ships Officers and Crew together with the propelling machinery spaces (engine room) fuel tanks and navagating spaces. The vessels port dues are usually levied using the net tonnage measurement.

The DWT is the term normally used to describe the carrying capacity of oil tankers and bulk carriers however the gross tonnage figure is normally used for cruise liners, ro-ro vessels, ferries etc to illustrate their "size"

LWT + DWT = DISPLACEMENT

A long ton is = 2240 lbs or 1016 kg

A short ton or US ton is = 2000 lbs

A metric tonne is 2205 lbs or 1000 kg

I hope the above will be of some interest and use when discussing a vessels "size"
 

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Discussion Starter · #3 ·
Jeff Egan said:
Now Tmac is your Gross tonnage GT or GRT
It's a matter of taste Jeff, we used GT as a reference in our design calculations but GRT or gross registered tonnage is correct in your line of work. As shipbuilders we just like to be awkward bugg**s LOL So sitting on the fence AGAIN both are correct.
 

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I seem to recall that at one time shelter decks were not included in GRT some huge ships had a very small GRT as in the case of Car Carriers most of the car carrying decks were deemed to be shelter decks, this was put right in I think the early 1990s when GT was brought in. I remember some ships who had GRT of 10000 ton suddenly had it remeasured at 35000 ton. It was very good for us pilots who at the time got paid on GRT/GT
 

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Discussion Starter · #5 ·
As you say it's a minefield shipowners always tried to get the lowest measurement while harbour boards etc wanted the most they could get. I'm sure you remember the various ways owners would try and fiddle the figures with tonnage wells etc. Thankfully it wasn't our problem but it gave the BoT and LLoyds quite a few headaches and arguments with the owner. There were so many regulations and amendments it became a nightmare at times and the tonnage figures varied almost daily.
 

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You would think LOA and Max Beam and height would be simpler but as you say Tmac it sometimes benifits people to keep it complicated, easier to fiddle that way. When compulsary Pilotage was introduced on the Tyne the lower limit was set at 50 metres and suddenly ships that had been 50 metres became 49.99 metres overnight.
 

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I was always told you could only measure a ship by the people on it (Thumb)
 

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There was quite some controversy in the 50's-60's about the measuring of ships and especially in Holland and Western Europe for that matter you came accross GRT 's of 399 and 499, all to do with the restrictions on the number of crew and harbour charges.
The DWT on such ships could vary from 600 to even 1300 Tonnes.
During the 70's it all changed to the actual length of the ship.
By memory the cut off was then set at 75 metres so that GRT was of no further importance.
Hereby some data from another site which may explain a bit about shelterdeckers, half or raised, etc.
Scroll through the various topics.

http://www.kustvaartforum.com/viewtopic.php?t=272&postdays=0&postorder=asc&start=40

This site is in Dutch but some of the pictures may be clear enough to explain the confusion at the time.
Jan
 

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Jeff Egan said:
I seem to recall that at one time shelter decks were not included in GRT some huge ships had a very small GRT as in the case of Car Carriers most of the car carrying decks were deemed to be shelter decks, GRT/GT
There was an "Honourable Compromise" reached when it was pointed out to Car carrier Owners that due to their very low "Mickey Mouse" tonnage they could only expect the services of a new junior pilot with a very low tonnage licence in spite of being bloody great ships!!! I seem to remember some of the early Japanese ones were 650 ft long with a nett tonnage of about 2500,the same as a coaster.
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Tony C
 

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Good idea Tony, but on the Tyne we made no new pilots between 1977 and 2001 during which time the numbers dropped from 50 odd to 7 so it wasnt an option for us.
 

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My first thought was -- with a tape measure -- perhaps thats why I never quite made it !!
 

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I always thought that the universal standard measure for ships was the Firkin;
firkin big, firkin heavy, firkin hot, firkin cold......etc!

Regards

Allan
 

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Nairda59 said:
My first thought was -- with a tape measure -- perhaps thats why I never quite made it !!
My first job on my first ship (Brocklebank's "Malancha" ) was just that. In drydock in Glasgow spent days with the Third Mate, a Surveyor, and a very long tape measure remeasuring the tonnage.
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Tony C
 

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Nairda59 said:
My first thought was -- with a tape measure -- perhaps thats why I never quite made it !!
Me too Nairda59 and also wondered, did the bowsprit count as part of the length?!!! (EEK)
 

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Discussion Starter · #18 ·
Coastie said:
Me too Nairda59 and also wondered, did the bowsprit count as part of the length?!!! (EEK)
Oh Coastie I'm surprised at you, and you one of Her Majesties finest too. Is that length OA or length BP? LOL
 

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We measure length "Between Perpendiculars" here Tmac!! LOL (Cheeky bu**er!)
 
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