What is a Ton in Boat Weight

[sepharad]

Originally Posted by Orion Jim

It is a measurement of internal volume, nothing to do with the weight of the vessel. When you say “the documentation” I presume you are referring to your USCG document.

https://www.dco.uscg.mil/Our-Organiz...tation-Center/

https://en.wikipedia.org/wiki/Gross_tonnage

THIS would be my answer. When I registered my boat I had a Tonnage Survey. The was no weighing. It was measurement of the INTERNAL VOLUME / CAPACITY.

In my case a 27 foot vancouver was 6.02 Tons. God only knows what the boat weighs.

[Simi 60]

57 metric tonnes (62 US ton) when lifted a few months ago
Half fuel, near zero water
Fill her up and add another 6 tonne

[RaymondR]

Originally Posted by Mike Burch

Boatyarddog, I fear you may have been misinformed. A long ton is, as stated several times above, a weight of 2,240 pounds. In other words it is simply one of many units of mass (and commonly weight). For many centuries it was the only type of ton there was. It may be used to state displacement or anything else. "Displacement tons" may therefore be measured in long tons, but not every long ton is a measure of displacement, so "long ton" and "displacement ton" are not synonyms.

The displacement of a vessel can be stated in any weight unit you like, short tons, long tons, tonnes, pounds, kilograms...

The "tonnage" of a vessel, again as stated several times above, is meaningless unless the type of tonnage (gross, net, Thames, displacement, deadweight, or whatever) is also stated.

The Imperial unit of mass, is or was, slugs. Don't have a clue as to the derivation.

And, we don't want to go anywhere near the length and area measurements with it's chains, rods and roods.

[rotrax]

Originally Posted by Adelie

For the purposes of calculating “Tonnage” a ton is 100 cubic feet.

I believe this goes back to tuns of wine.

Correct, but not neccesarily wine.


A Tun was the largest size barrel, very often used for liquids like Beer, Wine and brewed Vinegar. Early Thames Measurement of a ship was by how many of these large barrels a ship could hold. Later, when Education made it possible for the space to be calculated, the term changed to Ton and other antique measurements were standardised. The local brewery in Abingdon - Morelands - had an open day. I remember being advised that four of their heaped wooden Malt Shovels used on the drying floor equaled a Bushel. The dried barley and hops were transported internally by Bushel baskets, the workers being paid by how much they shifted.



A popular pub name in the UK is "The Three Tuns" the pub sign showing three of these large barrels.


I visited the Sarsons Malt Vinegar brewery in the 60's with my father. These large barrels were redundant but were used as museum pieces to show the history of Vinegar Brewing. I was told it is a far more critical process than beer making.

[goboatingnow]

Net tonnage for pleasure boat is of course nonsense. Mine has been 4 , 6 and 9 tons under different registries for the same boat.

[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.

[RaymondR]

Hi Stew.

"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."

My understanding of the relationship with Archimedes principal is that if the density of the fluid changes the volume displaced will but the weight displaced will remain constant.

[Cadence]

Originally Posted by peghall

An informative and entertaining explanation of ships tonnage that I found years ago and decided it was a keeper:

Tonnage has nothing to do with the weight of your boat. It is a measure
of how much wine a vessel can carry.

The word "tun" was originally a size of a cask used to ship wine from
Spain & Portugal to England. In 1347 a tax of 3 shillings per tun was
imposed and this was called "tonnage." A ship's size became known by the
number of casks it could carry, and the word tonnage started being used
to describe a ship's size.

It was found that if you took the length x the breadth x the depth of
the hold under the deck and divided by 100 it was close to the number of
casks. That is where we get the "Measurement ton" of 100 cubic feet per
ton.

There are several kinds of tonnage: The first two are used by the tax
collector. The next two are used by designers. The fifth and sixth are
used by freight salesmen and canal operators and the last one is used by
the USCG for documenting boats.

Gross Tonnage - is the internal volume in cubic feet of the vessel
minus certain spaces above the main or "tonnage" deck, like stacks and
ventilators, which are called "exemptions" .

Net Registered Tonnage - is obtained by deducting from the gross tonnage
the volume of space that can't be used for paying cargo or passengers,
that is to say the space occupied by the engines, the crew's quarter,
the stores, etc.

Displacement Tonnage - is the actual weight of the water "displaced" by
the ship and is usually quoted in long tons of 2240 lbs.

Light Displacement Tonnage - is the weight with nothing in it.

Loaded Displacement Tonnage - is the fully loaded weight to the maximum
and is on her summer draft in salt water.

Deadweight Tonnage - is the difference between Light and Loaded
Displacement Tonnage....the actual carrying capacity of the vessel.

Panama & Suez Canal tonnages - these are different from the internationally accepted definitions. There used to be a lot of variations between countries and the canal owners thought they were being conned, so they came up with their own definitions.

Simplified Measurement System - The USCG decided that all this was way too much for bureaucrats to deal with for yachts so they came up with
their own formula:

Take the horizontal distance between the outboard ends of the boat not
including rudders and bow sprits. Multiply that by the maximum beam outside to outside.
Multiply that by the distance from the sheer line not including bulwarks
or cap rails to the outside bottom of the hull not including the keel.
Add the volume of the deck house/cabin top. Multiply by .5 for sailboats and .67 for power boats.
Divide by 100.

This will give you the "Gross Tonnage". Net tonnage is 90% of gross for
sailboats and 80% for power boats.

It should be obvious to anyone who's managed to get this far that your boat's "tonnage" no longer has anything to do with anything real; it only exists in the mind of some government bureaucrat.

--Peggie

p.s. In days of yore, casks that arrived in por too damaged to be saleable to their purchasers were called "rummage" and offered for sale at bargain prices...the origin of the term "rummage sale."

Peggy, what the hell are yacht (boat) mfgs. using in their literature? I'd guess weight. A travel lift operator would care less about the amount wine his slings can take. They may like a beer as thanks after blocking.
I thought I had read that only a head was excluded in the below deck volume. It's a moot point since it is an archaic system. Ships?

[anacapaisland42]

Sorry, a long ton is 20 CWT (hundredweight) which is 20 * 112lbs or
2240 lbs
LOL

Originally Posted by tkeithlu

A short ton is 2,000 pounds
A long ton is 1,000 kilograms, or about 2,200 pounds.

You have a monohull with substantial ballast. I'm still impressed that it's 18,000 pounds in a 41 ft boat. That seems high, but it's been awhile since I sailed a 40' Rhodes with 6,000 pounds of ballast. Maybe design has changed.

OK, but which was being used when someone says "tons?" Are they otherwise talking American, as in feet, or are they talking like the civilized world, as in meters?

[Adelie]

And 1,000kg is a tonne.

[Mr B]

To Make it easy, A cubic yard will displace one Ton of water,
So 5 cubic yards of sealed containers on board, My boat wont sink, No matter how big the hole in it is,
That can be in sealed bulkheads, Holes full of sealed milk containers, Blow up mattresses any thing that cant be floated overboard,
My boat weighs 4.5 Tons on the travel lift,

[Adelie]

1 cubic yard = 27 cubic feet.
At 64lb/cubic foot for seawater that’s 1728lb.
Short ton is 2,000lb, metric tonne is 2200lb and a long ton is 2240lb.

[jmschmidt]

The Gross Registered Tons, or GRT, on a US Coast Guard Documentation Certificate has little or has nothing to do with the actual weight of a vessel.

Simply put it is a fictitious formula that calculates the physical volume of a vessel's theoretical capacity to hold persons and or cargo which it further converts to "Tons."

For small recreational vessels the simplified USCG Form No. 5397 can be used to calculate GRT. For larger commercial vessels this is usually calculated by specialist surveyors trained to make these calculations.

Certain areas on commercial vessels can be sealed off from use as storage or passenger space to reduce the useable space and therefore the GRT. Where I live there is a dinner cruise ship which is a couple of hundred feet long and carries up to 300 dinner passengers, yet its GRT is only 99 tones. This allows the vessel to be commanded by a 100-Ton captain. If the actual vessel weight were used to determine crew qualifications this vessel would require at least 2,000-Ton captain who would get paid a lot more.

I have a 50-Ton license, but I can operate a 6-pack OUPV vessel up to 100 tons.

The previous 12-meter America's Cup boats were not 12 meters in length. They were more like 20 meters in length, but the arcane formula used for the calculation took in many variables which had to produce and end number result of 12 meters for the boat to compete for the Cup.

Go figure.

[MicHughV]

The English say "spanner"...the Yanks say "wrench".....but it's still the same tool.

For the life of me, I don't understand why the USA clings to feet, inches, pounds and miles...????

Metric is infinitely simpler, easier and more practical....

[boatpoker]

Originally Posted by capt jgw

It gets more confusing yet. When they measure a vessel to determine registered tonnage, they don't measure the whole boat. Only "watertight volume."

This is incorrect, "watertight volume" is irrelevant. Gross Tonnage is the entire volume of interior space and depending on design may include some deck space. NET Tonnage is Gross minus contra. Contra may include engine space, galley space, wheel house and/or crew quarters depending on a number of other factors.

PS. I am a Transport Canada Appointed and IMO Recognized Tonnage Measurer.