registered tonnage quick reply needed please

[Sinbad2222]

Re: Lead and water .... silly billy ....

Archmedes is quite right and is there all the time if you need him! His principle (which which applies to a body floating or not floating) is as follows:- " When a body is partially or totally immersed in a liquid it experiences an upthrust equal to the weight of displaced liquid"
A body will sink if the upthrust is less than it's weight.
A body will sink until the weight of the displaced liquid equals the weight of the body, it's then floating and thus the weight of a floating body is the same as the displacement.
- simple really!

 

[Guest]

Pulling the wool over their eyes !!!!

Refer back to my comment about Bales ... Wool / Cotton / other materials of similar style etc. were carried in bales.

 

[Dipper]

Of course Barnicle is demonstrating the principles admirably.

Assuming his bath was full initially, the weight of his floating toys would equal the weight of water that had to be mopped up from the floor when they were first put in the bath tub. However, the weight of Barnicle does not equal the weight of water he has displaced because he is not floating. However, the apparent loss of weight of Barnicle does equal the weight of water he has displaced.

I have had to make the assumption that Barnicle has not splashed vigorously in the bath (he probably has) and that he hasn't broken wind under water (also likely to have happened). /forums/images/graemlins/laugh.gif /forums/images/graemlins/grin.gif

 

[Bajansailor]

Re: measuring GRT of a multihull

Re if the accomodation on the bridgedeck is included in the calculation for gross tonnage - yes it is. So the gross tonnage of your cat would basically be the total enclosed volume, including both hulls and the bridgedeck. Before I am shot down for generalising, there are various deductions and allowances in the (big ship) rules that can be applied, but total volume within is a good general ball park figure.

Re calculating weight at the design stage, the same principal applies to both small yachts and big ships, as mentioned earlier by sbc. Before the vessel is launched the displacement at any draft can be calculated using Simpsons rules - it used to be all done tediously by handcalcs, but now a computer will wizz through the calcs with ease. A weight calculation is also carried out, where the weight of every known component on the boat or ship is added up - this includes the weight of (eg) the steel frames and shell plates (or the fibreglass hull), and all the outfit items - the sky is the limit as to how accurate you want to be.
A computer spread sheet helps a lot here.....

Once you have the calculated weight of the boat, and you have calculated the displacements for a variety of different drafts (and perhaps drawn a graph of displt vs draft), then you can estimate what draft the boat will float at before she is launched. Useful for deciding where to paint the waterline!

If anyone would like to bean up further on this subject, may I commend to you an excellent little book called 'How to design a boat' by John Teale. He explains everything to do with weights and displacements in a very readable and easy-to-understand way.

 

[vyv_cox]

Re: Pulling the wool over their eyes !!!!

Yes, I know what a bale is /forums/images/graemlins/smile.gif I was told that Thames tonnage was specifically wool and that Part 1 meant that only.

 

[Guest]

Re: Pulling the wool over their eyes !!!!

I had a feeling you knew !! But actually the people who told you about wool are not strictly correct .... wool is only 1 of the commodities that started it all ...............

We could of course get intoi all sorts of discussions over this hairy salty-sea-dog question ... ie :

Suez GRT / NRT
Panama GRT / NRT
Thames RT
Internationally designated GRT / NRT

shall we go on ?
/forums/images/graemlins/wink.gif

 

[billcowan]

re: favourite topic.

AAHHH this thread just keeps getting better.

What about the anchors then? do they count as tonnage, tunnage or just dunnage.

Then there is the chain, or should it be warp, and how much.


PS. thanks bajansailor, thats how I figured they did it.
Incidentally have you seen the rig they use for testing stability?

 

[chinita]

Re: re: favourite topic.

Funny that nobody from Pt 1 Registry has commented!

 

[Bajansailor]

Re: anchors and stability

Depends what sort of anchors you have - the Rocnas and other new fangled types would be in the Ships Constant (except it isnt) kgs as they are too new to be in the tonnes, while the wine barrels (not very efficient admittedly as anchoirs, but no worse surely than Hylas' latest creation) would be tuns, and the old fangled Navy and Fishermen anchors would be included in the Lightship tonnes. /forums/images/graemlins/smile.gif
Chain could be tonnage, while warp (if you have enough) could be dunnage (of sorts)....
Re rig for testing stability, do you mean inclining experiements to find out where the centre of gravity of the vessel is?

 

[HeadMistress]

A friend wrote this wonderful treatise on tonnage:

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.

A bit of additional trivia:
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. another word of French maritime
origin.