Gross Tonnage

laika

laika

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In a recent news story which I won't reference as I don't wish to trivialise its tragic content with technical pedantry, a passenger ship was referred to as an "X-tonne vessel". Looking up the vessel its Gross Tonnage is X. Would I be correct in thinking that the "tonne" is only a metric unit of weight and nothing to do with "tonnage", or is the tonne also a unit of volume and relates to Gross Tonnage as I believe the Register Ton related to Gross Register Tonnage?
 
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N THE BEGINNING was created the Imperial Ton
= 2240 pounds (lbs.)
= 20 Hundredweight (cwt) i.e. 1 cwt = 112 lbs.
AND YEA, when the Pilgrim Fathers landed on Plymouth Rock, they said
VERILY: One Hundredweight should be one hundred pounds and one Ton should be 2000 lbs.
THUS WAS CREATED the US Ton.
BUT SORELY DISPLEASED were the merchants and traders when they became aware that the colonials were making 10% on the side.
THUS IT CAME TO PASS that the British traders did declare that their galleons would, in future, also use measures of 2000 lbs, and declared that this measure should be named the Short Ton.
MANY MOONS PASSED, and the tribes of Europe did send their high priests to council one with the other, whereupon they begat the EEC (EU).
THE TRIBES OF THE CONTINENT did pour scorn upon the Ton and the Short Ton, and being more in number than the Britons did ordain that all nations should obey The New Commandment: Thou shalt worship the Tonne which equates to 1000 kilograms (kg).
THIS DID SORELY DISPLEASE THE BRITONS, since this new measure did contain 2205 lbs., but it came to pass that more tribes came to join the EEC and the Britons were obliged to pay homage to the Tonne.
THE EEC DID COMMAND that tablets of stone be carved, on which was writ:
1 IMPERIAL TON = 2240 lbs.
1 SHORT TON=1 US TON = 2000 lbs.
1 TONNE = 1000 kg = 2205 lbs.
THUS WAS THE CONFUSION CREATED.

And then we consider the nautical aspect and the difference between gross weight and displacement. I think I need to lie down, I have a headache coming on!
 
Tonnage is a noun and is the weight in tons of cargo or the measurement of cargo space carrying capacity in tons. Tonne is a noun and is also known as the 'metric ton' which is 1000 kg of mass and has nothing to do with cargo carrying capacity or classification. This is how I understand it.
 
Gross tonnage doesn't have any units, it's worked out by some complicated formula.
The old Gross Registered ton was 100 cubic feet volume. It's almost unheard of for journalists to get it right, except Sea Breezes or something, cheers Jerry
 
JumbleDuck said:
Isn't tonnage a measure of volume, being a measure of how many tuns (ie sodding great barrels) can be carried?
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Yes, but ultimately it is an indirect measurement of weight that can be carried. In a modern sense oil is sold by the barrel, but ultimately it is sold by the tonne as that determines how many trains or ships are needed to move the stuff about.
 
In brief:

Gross tonnage is the internal volume in cubic feet divided by 100. Additions can be made for spaces above the "tonnage deck"

Net tonnage is the gross tonnage minus the non earning parts of the ship (ie space for engines, fuel, stores, navigation, crew etc )

Displacement is equal to the actual weight

Deadweight tonnage is the difference between light and loaded displacements.

Thames measurement is calculated from (L-B) x B x ½B / 94 where L and B are the length at deck level and beam

For more detail see one of the following


Reeds etc use to include this info in the old days

You'll find it in The Oxford Companion to Ships and the Sea which you can access online if you have a library card.

No doubt also in Wikipedia
 
jerrytug said:
Gross tonnage doesn't have any units, it's worked out by some complicated formula.
The old Gross Registered ton was 100 cubic feet volume. It's almost unheard of for journalists to get it right, except Sea Breezes or something, cheers Jerry
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On a point of order, it is almost unheard of for a journalist to get anything right, unless the piece on the Internet he lifted his story from had previously (probably accidentally) got it right.
 
JumbleDuck said:
Isn't tonnage a measure of volume, being a measure of how many tuns (ie sodding great barrels) can be carried?
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Yes, the tun was the ISO container of its day, and ports were equipped with lifting tackle to handle it. It could contain anything - building stone, grain, oil but usually wine. Cheers!
 
Resolution said:
Windlipper
That was quite beautiful!
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Yes, but completely irrelevant as far as the original question is concerned! As usual VicS has the right answer - or you can google the term and get the meaning confirmed from a variety of reliable sources.
 
VicS said:
In brief:

Gross tonnage is the internal volume in cubic feet divided by 100. Additions can be made for spaces above the "tonnage deck"
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I believe you are describing Gross Register Tonnage. I gather this was replaced by the metric "Gross Tonnage" which the wikipedia page describes as "unitless". Me being me I did do a reasonable amount of research before posting and everything I've found points to a description of a vessel with a GT of 22000 as a "22000 tonne vessel" being incorrect which is why I posed the question. My small doubt was that if the "Register Ton" existed (100 cubic feet) as the unit of "Register Tonnage" perhaps, despite what wikipedia etc. tells me, the "tonne" might be in common parlance as the unit of the metric and officially unitless "Gross Tonnage".

However no-one seems to have disagreed with wikipedia on this so my original assumption (that the description was erroneous) stands.

I suspect that this came from a news agency as multiple sources (Guardian, Indie, BBC, MSN...) are using the same "22000-tonne vessel" phrase. Actually the Grauniad originally had it described as a "22-tonne vessel" but they corrected that pretty quickly.
 
laika said:
I believe you are describing Gross Register Tonnage.
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You have confused me now.

What I posted was an attempt to shorten the descriptions in an old Reeds ... from the days when Reeds was Reeds


The Oxford Companion to Ships and the Sea has this to say:

tonnage,

originally the charge for the hire of a ship at so much a ton of its burthen. It was also a tax, first levied in 1303 by Edward I of England, on all imports brought by ship into England. A second tax, known as tunnage, of three shillings on each tun of wine imported, was levied in 1347 by Edward III.

It was from the first of these meanings, the cost of the hire of a ship, that the word tonnage came into use as an alternative to burthen. Although tonnage was still theoretically based on the number of tuns of wine that a ship could carry in its holds, it became necessary, both for taxation purposes and for calculating the harbour dues payable by a ship, to devise a rough and ready formula by which the tonnage could be quickly calculated. It was found, in the general design of ships of those early days, that the vessel's length in feet, multiplied by its maximum beam in feet, multiplied by the depth of its hold below the main deck in feet, with the product divided by 100, gave a reasonably accurate measurement of its tonnage, and this was the formula used for measuring warships as well as merchant vessels.

In 1694, when a law was introduced in Britain requiring the marking of a waterline on merchant ships, both when in ballast and fully laden, this tonnage formula was officially adopted, though marginally amended to make the product of length, beam, and depth divisible by 94 instead of 100. This remained the standard of ship measurement until 1773, when more accurate limits of measurement were established by a formula known as the Builders Old Measurement (BOM). This remained in force until the advent of iron for shipbuilding and steam propulsion revolutionized the design and shape of ships.

The BOM served its purpose well for the typical bluff-bowed, full-bodied ship of the timber and sail era but had no relevance to the longer, finer hulls of the iron ship in which the ratio of length to beam increased from the average three to one to four, five, and even six to one. In place of the old BOM a new calculation, known as Moorsom's Rule, devised by the Admiralty at the request of the Board of Trade in the mid-19th century, was introduced. The total capacity of a ship's hull below the upper deck was calculated in cubic feet and, by dividing it by 100, the resultant figure became known as a ship's gross tonnage.

But this figure did not, of course, bear very much resemblance to its cargo-carrying capacity, since it was calculated on the total hull space below the ship's upper deck and made no allowance for space taken up by crew's quarters, ship's stores, fuel, engines, etc. So a second calculation was made of the capacity in cubic feet of these spaces and, still taking 100 cubic as equivalent to one ton, was deducted from the figure of its gross tonnage to give a net tonnage.

Both these tonnages are known as register tonnages as they are entered on the ship's certificate of registration. It is on the figure of a ship's net register tonnage that such charges as port and harbour dues, dues for navigational aids, towage charges, and salvage assessments are normally levied.

Another tonnage measurement of a merchant vessel is deadweight tonnage, normally shortened to dwt. This is a measurement of the weight of the cargo it carries based on the long ton of 2,240 pounds (1,017 kg). The figure is arrived at by calculating the amount of water displaced by a ship when it is unloaded, but with its fuel tanks full and stores on board, and the amount of water similarly displaced when it is fully loaded with its cargo holds full. The difference expressed in tons (35 cubic ft of seawater = one ton) gives the ship's deadweight tonnage.

Naval vessels are usually measured in terms of displacement tonnage. This is the weight of the water a ship displaces when it is floating with its fuel tanks or bunkers full, and with all stores on board. This, at the rate of 35 cubic feet per ton, is the actual weight of the ship, since a floating body displaces its own weight in water. During the last half of the 19th century, and for the first half of the 20th century, yachts were measured by the Thames Measurement rule.

The introduction of the metric system into most countries that previously used the imperial measurement has led to ships' displacement being given in metric tonnes. However, as the weight of the metric tonne (1,000 kg) and the avoirdupois, or imperial, long ton (2,240 lb) are so close—there is only 1.16% difference between the two—large-scale reregistration of vessels has not been necessary.

In 1969 the International Maritime Organization adopted the International Convention on Tonnage Measurement of Ships which entered into force in 1982. This was the first successful attempt to introduce a universal tonnage measurement system, the new rules applying to all ships built on or after 18 July 1982. Those ships built before that date were allowed to retain their existing tonnage for twelve years before they needed to be remeasured. The Convention meant a transition from the traditional gross register tons (GRT) and net register tons (NRT) to gross tonnes (GT) and net tonnes (NT). Gross tonnage forms the basis for manning regulations, safety rules, and registration fees, while both are used to calculate port dues. The gross tonnage is a function of the moulded volume of all enclosed spaces of the ship, while the net tonnage is produced by a formula which is a function of the moulded volume of all cargo spaces of the ship.
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Like an idiot, I recently attempted to show SWMBO's father how much better (because I believe it's easier) metric measurement is, for estimation of volume and weight of water...

...I told him I could easily guess the weight of a cubic foot of water, instantly, by converting the measurements into metric...so, in my head, quickly, I did: 30cm x 30cm x 30cm...

...equalling 27,000 millilitres, or 27 kilos. Trouble was, the wily old sod had been doing rapid calculations of his own, and had written on his piece of paper, 57lb...

...which was also pretty damned close. :o

I realise there are reasons behind old-fashioned scales of measurement, and they must have been enduringly workable for the businesses which used them...but it had never occurred to me that anyone bought up with those crazy thru'penny bits, grains and hundredweights was likely to be just as efficiently numerate, despite suffering the awfulness of imperial.
 
dancrane said:
Like an idiot, I recently attempted to show SWMBO's father how much better (because I believe it's easier) metric measurement is, for estimation of volume and weight of water...

...I told him I could easily guess the weight of a cubic foot of water, instantly, by converting the measurements into metric...so, in my head, quickly, I did: 30cm x 30cm x 30cm...

...equalling 27,000 millilitres, or 27 kilos. Trouble was, the wily old sod had been doing rapid calculations of his own, and had written on his piece of paper, 57lb...

...which was also pretty damned close. :o

I realise there are reasons behind old-fashioned scales of measurement, and they must have been enduringly workable for the businesses which used them...but it had never occurred to me that anyone bought up with those crazy thru'penny bits, grains and hundredweights was likely to be just as efficiently numerate, despite suffering the awfulness of imperial.
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Awful for you poor benefited-from-all-those-years-of-the-finest-education-system-ever youngsters, maybe. Us oldies can hack any sort of measurement.

Anyway, a cubic foot of fresh water always weighed 62.4 lb in my day.
 
Grumpybear said:
...a cubic foot of fresh water always weighed 62.4 lb in my day.
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I think that's the point...SWMBO's pa hadn't given my question much thought, but still came up with a reasonably accurate response. I had felt sure that the bloomin' awkwardness of NOT being able to count water's weight in equal units as the metric system uses to gauge its volume, would slow him up. It didn't, so credit to him, and all those of his education.

But I'm still delighted (and relieved) to be able to look into a space, judge its length, depth & height, multiply up, and instantly know what weight of water would flood it...

...most young people are unable to make that calculation, not because their maths is poor, but because they weren't taught that 1kg of water is also 1 litre and 1 cubic decimeter.
 
VicS said:
In 1969 the International Maritime Organization adopted the International Convention on Tonnage Measurement of Ships which entered into force in 1982. This was the first successful attempt to introduce a universal tonnage measurement system, the new rules applying to all ships built on or after 18 July 1982. Those ships built before that date were allowed to retain their existing tonnage for twelve years before they needed to be remeasured. The Convention meant a transition from the traditional gross register tons (GRT) and net register tons (NRT) to gross tonnes (GT) and net tonnes (NT).
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Hmmm...So the Oxford Companion to Ships and the Sea disagrees with wikipedia and seems to be happy to use "Gross Tonnes" for "Gross Tonnage" implying that the "tonne" is the unit of measurement for "Gross Tonnage". From what it says there, it wouldn't be incorrect to talk about a "22000-tonne vessel" when referring to a ship with a gross tonnage of 22000 (so my initial supposition would be wrong).

Grumpybear said:
Awful for you poor benefited-from-all-those-years-of-the-finest-education-system-ever youngsters, maybe. Us oldies can hack any sort of measurement.
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Those of us who benefited from not having to learn the arcane factors to convert between rods, chains, poles., perches, stone, nails scruples and sacks have been able to devote those parts of our brain to the technological challenge of enabling the world's population to view amusing videos of cats on a scale the older generation couldn't even imagine...
 
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