Talk:Deadweight tonnage

Add Link to spanish version of the article.

Please, someone add the Link to spanish version of the article.

http://es.wikipedia.org/wiki/DWT

Thanks —Preceding unsigned comment added by Fernando Zo (talk • contribs) 18:41, 9 June 2009 (UTC)

Weight or capacity?

This article says that deadweight tonnage is a measure of weight and is measured in tonnes, but the box below, and the article displacement both say that d.w.t. is a measure of capacity, which suggests a volume. Which is the right version? Goochelaar (talk) 13:53, 16 July 2010 (UTC)

"Capacity" is not restricted to volume. For example, the capacity of a crane is always measured as the weight it can safely lift at a specified radius. For ships, the same thinking (mostly) applies. Of over-riding importance is the total weight that the ship can carry without sinking. After that, the actual volume may be significant but the density of typical cargoes will be taken account of at the design stage of the ship. —Preceding unsigned comment added by 82.5.88.129 (talk) 12:47, 10 August 2010 (UTC)

The nautical term 'tonnage' was originally a measure of both volume or weight depending on whether the cargo was solid or liquid. In the Middle Ages and later, liquid cargoes such as wine were carried in large barrels called 'tuns'. The size of the tuns was fixed and so the number of tuns a ship could carry was also a measure of the amount of liquid (volume), e.g., wine, that it could carry, whilst at the same time it was also the amount of the space it had allocated to the tuns, i.e., the area (volume) available in the hold. Each filled tun weighed the same and so the cargo would have the same weight in any ship as long as the number of tuns was the same. When ships later became more specialised, the tanker ships carrying liquids such as oil and similar, no longer measured the amount of space taken up by the tuns, but started using the weight of the cargo as a measure of ship capacity instead - the important thing for a ship owner or shipper is the amount of cargo carried. Ships that carried general dry cargo or passengers continued to use the are/volume meaning of the tun as the cargo itself was less dense than the liquid ones. The area/volume ton was later fixed as 100 cubic feet.

BTW, the term 'deadweight' originally specified that the cargo was not liable to move during the voyage, i.e, it was in a fixed position in the ship once loaded and could be left alone by the crew without any additional handling, as contrasted with 'liveweight' which applied to cargo such as passengers, and livestock which, if it got out of its pens, that could move around on the ship possibly significantly affecting the ship's trim in bad weather, whilst also needing to be fed and watered, etc.

That's why tankers and bulk carriers are measured in deadweight, whilst passenger liners and ferries are measured in Register tons - the former is the weight in tons of the cargo, the latter is (or was) the amount of deck space and hold space (in multiples of 100 cu ft) allocated to passengers, dry cargo, etc. Both systems give an idea of the carrying capacity of the vessels, which is what's important for ship owners and shippers.

Warships are measured by displacement (i.e., actual weight if put on scales) as when the rules were laid out the armoured ship had made its appearance and the amount of armour carried was reckoned to give a good idea of a ship's fighting ability. Previously warships had been rated by their number of guns.

So the original 'tun' had three meanings depending on the ship and cargo carried:

• the amount of liquid cargo inside the tun, i.e, the actual volume of liquid, e.g., wine, carried by the ship
• the amount of space taken up by the tun in the hold, i.e, the hold or deck area occupied by the volume of a tun, full or empty. If no tuns of wine were to be carried on a particular trip then this space could instead be used for transporting other, dry goods.
• the weight of a filled tun, i.e, the weight carried by the ship per-each filled tun - this combined weight of a single tun and the liquid inside it amounted to roughly what would later became the long ton, 2,240lb - they were big barrels these tuns. This 'long ton' would eventually be the measure used for deadweight tonnage and also for warships' measures of displacement.

These categorisation were eventually formalised by the British, via Lloyd's Register and Lloyd's of London, in the nineteenth century and so are naturally somewhat logically-illogical. But as long as ship owners and shippers knew which one was needed, and for which type of cargo they wanted to carry, they made perfect sense.

So in short, the correct 'tonnage' measure to use in relation to a ship depends on the type of cargo carried and on the purpose of the ship - tankers, passenger ships, or general dry cargo ones. — Preceding unsigned comment added by 80.7.147.13 (talk) 22:19, 8 June 2012 (UTC)

Units

The term "deadweight tonnage" might be old term that carries a lot of tradition. It is nevertheless contradictory in terms, as the unit for weight is Newton, not ton, which is a unit for mass. --Sigmundg (talk) 11:46, 20 July 2011 (UTC)

You're being needlessly pedantic. Outside scientific contexts, the terms "weight" and "mass" are used interchangeably and "weight" is much more common. Since most of us spend our whole lives at essentially constant distance from the earth's centre, weight and mass are proportional anyway. Have you ever heard somebody say they're going on a diet to lose mass? (On the subject of pedantry, the unit of weight is the newton, with a lower-case "n" unless its position in the sentence requires a capital.) Dricherby (talk) 13:16, 22 April 2012 (UTC)