Gross Tonnage figure?

Norman_E

Norman_E

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I have just received the application form for a ships radio licence, which asks for gross tonnage of my yacht (based on I00 cubic feet equals 1 ton). All I know is displacement of 9.8 tons. Does anyone know the gross tonnage of a Jeanneau 45.2, or can I just put down the displacement? Alternatively is there a rough and ready formula for deriving gross tonnage from LOA and beam?
 
To arrive at the legal definition of gross tonnage, 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.

A bit of trivia...

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.

All that was just way too much for bureaucrats to deal with for yachts so they came up with their own formula as described at the beginning of this post. no longer has anything to do with anything real; it only exists in the minds of government bureaucrats.

Another word came from the same orgin: rummage. Rummage was the manner in which the wine casks were stored in the hold of the ship and came to refer to the whole ship's cargo. After a voyage any unclaimed and damaged cargo was stacked on the dock beside the boat and offered for sale - a rummage sale.
 
Don't worry about it! I've always put the displacement weight down and never had a problem, and that's with several boats over a 35 year period.
 
Thank you to all who replied. I will put down Steve Clayton's figure. I did not have all the dimensions required to work it out by the Headmistress' formula, but on guesstimates it gave me only slightly more. Interesting explanation, and I wonder how long it would take to drink a tun of wine?
 
This is the basis of the Thames tonnage i.e. the weght of the boat fully laden (it's carrying capacity.) it's just like a LGV, it has it's nett weight and gross weight.
Why you need this for a leisure craft? But it is a usefull calculation to know. My boat nett is 3.5 tons but it was registered at 6 tonnes London. So I understand this to mean that i can carry (in the terms of a Thames barge I suppose) 2.5 tonnes?
 
Maybe one of you can explain this one to me:

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

I understand that salt water is more buoyant than fresh water...but what does the season of the year ("summer draft") have to do with draft???
 
The density of water depends on both salinity and temperature, so a boat laden with a cargo will float much lower on her marks in hot water which isn't as dense as that Icelandic stuff
 
In summer, water is warmer, and therefore less dense. A ship will be slightly deeper in the water in summer than winter. The same effect happens when a ship sails from warm to cold water, or vice-versa. For example a merchant ship sailing from the Arctic to the tropics, will be deeper in the water on arrival. Plimsoll lines used to be marked for different water conditions, and cargo loading on old general cargo ships would take account of anticipated water conditions during the voyage. I am not sure whether the old markings are still used, but I am sure the same principles still apply.
 
[ QUOTE ]
Not just a pretty ol'girl with a bog-brush then?

[/ QUOTE ]

Believe it or not, my conversational abilities are not just limited to loos and pong! /forums/images/graemlins/smile.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/laugh.gif I actually have a wide variety of interests, some of which are boating related, but not all. I also have a great love of maritime tradition and lore...it breaks my heart to see so much of it rapidly becoming lost.

Thanks, Norman and Tome, for explaining "summer draft" to me. Does it really make THAT much difference?
 
it does makes difference but only on gigantically long and wide ships. The marks are from bottom NAW=north atlantic winter, W winter, S summer, T tropical and above thatfw for freshwater.
 
peggy, that lore hasn't been lost, though it's going that way. The terms of Thames Tonnage have been explained many times here, as have Plimsol lines. It's just that not many read the posts on the forums and learn.

If you do read and learn, and pass it on, you get castigated for learning. Go figure?
 
I agree ...... temp doesnt come into much it as when the water warms up so does the (metal) ship ......

winter/summer/tropical is used to decrease or increase the freeboard allowed so ensuring the vessel doesnt founder in bad weather.
so one can carry more cargo in a tropical zone and less in the n atlantic zone during the winter period.

salinity is allowed for with the fresh water allowance ..... meaning when the vessel reaches salt water it would not immerse the load line for the area

there is also a timber load line .... allowing a deeper draught as the cargo stowed on deck reduces the amount of water shipped, so reducing the vulnerability (in theory) ..... ship owners always want to squeeze the last bit of everything /forums/images/graemlins/smile.gif

but headmistress is awsome ........ /forums/images/graemlins/cool.gif
 
Summer Draft ..... this is the standard draft mark for a ship in temperate waters / regions. It is the mark that all others are derived from. You will find that normally it is same as Plimsoll line. There are exceptions - eg Timber Load-lines.

Winter and Winter North Atlantic are seasonbal in the geographic limits and are dictated to prevent vessels from being low in water for storms / winter periods.


Tropical as it says ....

So it would appear that Summer Draft is based on the normal Summer Loadline region ....

All based on dear old Samuel Plimsoll introducing Draft limits for UK vessels in 1870, act actually passed in 1890 .... all UK vessels over 80 Tons Net to have a loadline.

Also note that Salt-Water is deemed to be 1.025 density and when we survey vessels for loaded tonnage - Bulk Carriers etc. - we actually test the surrounding water to ascertain density and correct drafts / tonnage for the difference ... but thats another tale !!
 
So so .... biz is fair ....

Weather .... today is warm ... -6C ...... yesterday was a bit crisp - -12C all day ...
 
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