Deadweight tons ?

[pugwash]

I have a 30ft wooden ketch designed by Holman and built in 1969. On her registration certificate she's rated at 6.76 gross tons, 5.82 registered tons, and 9.5 tons Thames Measurement. How do I work out the deadweight tonnage, or is that the same as registered tons? Even a rough idea would help. I need to know for buying equipment. Thanks.

 

[Guest]

Tons of confusion ?

Weight ? Area ?

Lets confuse everybody by calling it Tons ?

A suitable case for conversion to metric ? It would be for me.

I have a stamp on a bulkhead in my boat which looks like a final pensions payout. What does it all mean ? No idea mate.

 

[Guest]

As far as I am aware - and I may be very very wrong because I haven't looked at the subject for nearly 40 years:

o Gross Tons = Ship + Bunkers and Stores + Cargo.

o Registered Tons = Ship with Bunkers and Stores but no cargo.

o Thames Measurement = Length x Breadth x Draft x Some Magic Number(s) that bring the figure to an estimated displacement in tons.

There - not much help was it!!??

Best regards )

IanD

 

[Shanty]

I think what you are looking for is the displacement. The numbers you list are all estimates of volume, none of which will give you a reliable idea of displacement.

If you are planning to have the boat lifted by a crane in the near future, the crane driver should be able to give you a rough idea of the total weight he is lifting. This, adjusted for anything removed prior to the lift, will give you displacement.

Alternatively, you could try contacting Holman & Pye to see if they can help:

Holman & Pye Yacht Designers
21 City Road
West Mersea
Colchester
Essex
CO5 8NE
Tel: 01206 382478
Fax: 01206 382478

 

[JonA]

Re: Tons of confusion ?

The old Observer Book of Ships had a nice clear explanation of the various "tonnages". Gross and net regestered tonnages are measures of volume origionating from a "tun" that is a cask used to contain liquid and is now 2.83cu metres in new money. Displacement tonnages are the weights/masses of a vessel
at various states of loading given in tonnes. Deadweight tonnage is the difference in displacement empty and loaded, in a big ship this is more or less equivalent to the mass of cargoe on board in tonnes. It's all the fault of history.

 

[Mirelle]

Not quite.

I am meant to know the answer, being in the business.

Let's see

Gross Tonnage - volume in cubic feet under the weather deck divided by 100

Nett Tonnage - ditto, less deductions for crew accomodation, propelling machinery and navigating spaces

These two derive from the mediaval tun of wine, which was about 100 cu.ft.

Displacement tonnage - what she weighs in air, i.e. the weight of water displaced when she floats.

Thames tonnage - l x B x 1/2B divided by 94 (originally a rating formula used by the Royal Thames Yacht Club, but actually a very good measure of the size of a cruising yacht)

Deadweight tonnage - the weight of cargo, fuel and stores that the ship can carry when floating at her Load Line. This is pretty irrelevant for yachts, which have neither cargo nor a Plimsoll Line (!) but your boat probably has a deadweight of about a ton anda half or so of crew, cruising gear and water.