What is a Ton in Boat Weight

[Andrew Lippman]

I believe the term tonnage as a measure of cargo capacity dates from the era of wine casks or something like that. On documentation, it measures volume of cargo-carrying spaces. It is not a measure of weight.

This matters because a boat greater than 500 tons requires a pilot in most US ports.

[skenn_ie]

Short ton is 2000lbs
Long ton is 2240lbs
Tonne (SI) is 2200lbs

[boatpoker]

Originally Posted by Andrew Lippman

I believe the term tonnage as a measure of cargo capacity dates from the era of wine casks or something like that. On documentation, it measures volume of cargo-carrying spaces. It is not a measure of weight.

This matters because a boat greater than 500 tons requires a pilot in most US ports.

as detailed in post #47

[mstr_cmdr]

Originally Posted by StuM

Using the term "Displacement tonnage" is what causes a lot of the confusion. Use of the expression is a common error.

Tonnage is not weight or displacement. As others have said it is a notional volumetric measure and should not be confused with or used in conjunction with the words "Displacement" or Weight" . Gross/Net Tonnage etc should never have the word tons or tonnes attached to them. Tonnage is a dimensionless quantity - it does not have units.

And strictly speaking, displacement and weight are not synonymous either.
Displacement varies with temperature and salinity of the water that the vessel is in. Weight doesn't.

2nd year physics suggests the following:
Weight is mass (absolute) x g (where g varies), and m (mass) remains constant.
Therefore, weight (w) varies, but the mass of the object is constant.

[Dsalvail]

In addition to displacement, volume, short and long tons, there's the one ton measurement common to all boats: the ****-ton. As in: "I had a ****-ton of problems with my engine before I sorted out..."

In my experience, the only one reliable measurement to be considered when buying a boat comes in arbitrary units of "****-tons".

Sailing, or transporting a vessel, I'll admit, requires more quantifiable parameters...

[Andrew Lippman]

Almost good point about displacement and weight. That's why we have Plimsoll lines.

A floating object will displace its weight in the fluid it is floating in. In water that depends on the season and salinity. It may be a different volume of water, hence the boat will float higher or lower, but it is the same weight.

[peghall]

Boat builders use displacement weight in their literature because that has to do with how much the boat draws, freeboard, land transport weight, and weight in the slings among other things that knowing how much the boat weighs matters.


--Peggie

[OneBoatman]

Nobody is wrong, read what Scorpius said. The tonnage of vessel is a rating formula which uses volume to estimate a vessels freight carrying ability. It was developed in order to estimate a commercial vessels cargo carrying ability and establish port fees. Some documented vessels may be documented relatively true to the formula, others not. What an owner puts on their application when they document a vessel is sometimes correct but not necessarily. I suppose if the USCG found clear abuse of this rating by the owner of a commercial vessel they could exercise their authority. The USCG still uses this estimate of space for documented vessels of all types. The formula is not a measure of the wt of a boat. There are tons and tonnes of other tons that are defined as measures of wt. Similarly in wartime, it is my understanding that when the USCG transfer of power goes from Homeland Security to the Navy this rating may come into play in their selection process as they elect to put a particular documented vessels in service.

[anacapaisland42]

The tun (Old English: tunne, Latin: tunellus, Medieval Latin: tunna) is an English unit of liquid volume (not weight), used for measuring wine,[1] oil or honey. Typically a large vat or vessel, most often holding 252 wine gallons, but occasionally other sizes (e.g. 256, 240 and 208 gallons) were also used.[2]

In one Early Modern English example from 1507, a tun is defined as 240 gallons.

[I]


—Untitled manuscript, consisting of a list of various customs duties, dated 15 July 1507[2][3][4]
The word tun is etymologically related to the word ton for the unit of mass, the mass of a tun of wine being approximately one long ton, which is 2240 pounds (1016 kg).QUOTE=anacapaisland42;3597326]Sorry, a long ton is 20 CWT (hundredweight) which is 20 * 112lbs or
2240 lbs
LOL[/QUOTE]

[boatpoker]

The word originally used when the measurement system was initiated by Queen Anne was "tun" . Somehow over hundreds of years that word morphed from "tunnage" to "tonnage". A "Measurement Ton" is now standardized as 100 cubic feet of cargo carrying volume capacity as specified in the IMO Tonnage measurement method.

tun -
1. a large beer or wine cask.
2. an imperial measure of capacity, equal to 4 hogsheads.
verbARCHAIC

[garychurch]

Sorry you are confused…

If you are referring to tonnage in your USCG Documentation it is a measure of carrying capacity volume. Do not confuse this with the weight of your boat.

[Dieseldude]

Boat and ship tonnage figures can be confusing. Official tonnage rating has little to do with the actual mass of the vessel. It is a measure used to establish taxation, fees, classification standards, and all that red tape kind of stuff. It is based upon 100 cubic feet of usable, or cargo, or revenue generating space. For example, an engine room is not included, since it is not a cargo or passenger occupied space.



How 100 cubic feet was equated to a tonne is bewildering. Perhaps a ton of baled raw cotton occupies 100 cubic feet, and cotton was a common cargo. The displacement tonnage is the most relevant figure for most purposes, since the vessel will displace a mass of water equal to its own mass. But there are problems with this as it will vary according to how heavily the ship is laden with cargo, people, and its own materials such as supplies and fuel. And larger vessels with ballast tanks will have this as a variable. The volume of water displaced varies with density of the water, which is a function of salinity and temperature. If you need to lift your boat out of the water or transport it by truck, the relevant figure is the displacement tonnage because it equates to the actual mass of the vessel. Because 1 long ton = 1.016 metric tonne, for most practical purposes they are the same. For draft and stability calculations of large vessels though, precision is important, since the average density of sea water is 1027 kg/m 3, as compared to fresh water at 1000 kg/m 3.

[parkstone bay]

Displacement is the weight, or better, the "mass" of the boat. This is the number to use for sizing a boat lifter, or your new cradle, or a trailer, or similar: even for how much effort Superman will need to lift the thing! It is expressed, depending on the area in which you live, in imperial pounds (lbs)/tons (= 2240 lbs), or kilos (kg)/tonnes (=1000 kg). In this context, the two are almost interchangeable as a tonne ("metric ton") is in fact 2204.6 lb); thus less than 2% difference.
All other "tonnages" are - nominally - imperial, but are intended to reflect other characteristics, and in particular the cargo capacity of a commercial vessel. A previous poster also correctly pointed out that the word "ton" in English had been conflated with the word "tun" (a cask of wine). My little MB has a "registered tonnage" of 2.60, calculated from nominal length of 6.34m x nominal breadth of 2.17m x depth (from topmost continuous deck) of 1.18m x 0.16. (The figure of 0.16 is a purely arbitary constant). Her actual mass, and therefore displacement, and the number I give my boat lifter team for transport purposes is rather less, at 2.25 tonnes. The various registered tonnages were used for calculating charges such as port dues, etc.; though I quite like the idea of having over 2 tuns or tons or tonnes of wine aboard! With my friends we could have a hell of a party!
Finally, google the words "tun" and "hogshead" - that way madness lies.

[glanrock]

I can't believe I read through this whole thread. Damn my curiosity!

[aqfishing]

GT has nothing to do with load carrying capacity. It is the enclosed volume of the vessel. That is usually your “tonnage”
Displacement or weight is what the crane scale should tell you.


Gross and net tonnage
“Gross tonnage” (GT) and “net tonnage” (NT) replaced “gross registered tonnage” and “net registered tonnage”, respectively, when the IMO adopted the ITC, which entered in force for all new ships in 1982, with existing vessels at the time having been given a migration period of 12 years. So since 1994 the GT and NT indices have been the only official measures of ships’ tonnage.

GT, the magic measurement based on which various dues will be levied and some statutory requirements imposed, is a factor of the internal volume of the permanently enclosed spaces of a ship from keel to funnel, while NT is the measure of the volume capacity of the permanently enclosed spaces of the vessel from keel to funnel, less the volume of certain non-cargo carrying spaces. GT and NT are calculated according to formulas described in the ITC.1

Weight measurement of ships
The following methods of ship measurement are based on the ship’s weight.

A ship’s displacement is the volume of water it displaces when it is floating, and is measured in cubic metres (m3), while its displacement tonnage is the weight of the water that it displaces when it is floating with its fuel tanks full and all stores on board, and is measured in metric tons (MT, equivalent to 1,000 Kg). The displacement tonnage is the actual weight of the ship, since a floating object displaces its own weight in water.2

A ship’s lightweight or light displacement is the actual weight of the ship with no passengers, cargo, bunkers, lube oil, ballast, fresh water, stores, etc., on board.

The loaded displacement is the weight of the ship loaded down to its load line marks, that is, loaded to its maximum capacity with passengers, cargo, bunkers, lube oil, ballast, fresh water, stores, etc., on board.

A ship’s deadweight is the difference in metric tons between the loaded displacement tonnage of the ship and the lightweight of the ship. Therefore, the deadweight can be a tool to express in metric tons the actual cargo capacity of the vessel. However, the difference between the loaded displacement tonnage and the lightweight does not reflect the cargo carrying capacity only, as deadweight also includes bunkers, stores, freshwater, etc. These factors will have to be deducted from the deadweight in order to come to the actual cargo carrying capacity in metric tons.

From - https://www.gard.no/web/updates/cont...ement-of-ships