Displacement and Gross Tonnage

[johnabbott893]

Her spec is Light Displacement of 7780Kg and a Gross Tonnage of 16.69 tons. Am I correct in that she weighs 7780Kg empty and is designed for a max fully ladened weight of 16.69 tons. Also, 16.69 tons is 16.96 tonns or a displacement of 16960Kg. This would be her gross displacement?

 

[pvb]

Good lord no! Gross tonnage is a theoretical figure based on the dimensions of the boat. You certainly couldn't add 9 tons of gear to her and expect her to sail properly!

 

[Tranona]

No, the displacement or weight is 7780kg. Light displacement is without fuel water crew and gear - typically on your size of boat would add anything between 1000 and 2000kg.

As mentioned Gross Tonnage is based on a formula that measures the carrying capacity (essentially a cube measurement calibrated against "tuns" - standard size wine barrels!). Reason why that is quoted is that light and harbour dues in commercial ports are based on that figure. However, for yachts it has no practical meaning in most situations, although is still used in part of the calculation for harbour dues in Greece!

 

[MIKE_MCKIE]

Further to previous, Gross tonnage is basically the total internal cubic capacity of the boat, measured in cubic feet and divided by 100. ie 100 cubic feet = 1 Gross ton. It is actually GRT or Gross Registered Tonnage. The other one with no particular relevance to yachts is NRT or Nett Registered Tonnage, which is GRT less certain internal spaces that include the galley, storerooms, engine room etc & is basically the cubic capacity available for the carriage of cargo.
I'm sure that you really really needed to know that, but who can resist displaying knowledge so painfully gained over 50 years ago, and still remembered?!?!
A minor miracle in its self !

 

[Tranona]

Ah! The Net measurement is relevant because it takes out machinery space, chart space and best of all accommodation space for apprentices which always amused my daughters, particularly as there is no allowance on my boat!

These "fiddle factors" would be used to minimise Tonnage and therefore minimise dues!

Nowadays one can just lie and put down any figure you want on your SSR because nobody checks (as far as I know!)

 

[vyv_cox]

<<< although is still used in part of the calculation for harbour dues in Greece! >>

That's one of the best arguments in favout of having an SSR instead of a Part 1. My displacement is around 6 tons and my Gross Tonnage is 9 and a bit. The Greeks just want the weight, but only the GRT is shown on the certificate, so that's the one they take. Only costs me an extra Euro per time but could be more signnificant with a bigger boat.

 

[Tranona]

Unfortunately my Bill of Sale has gross and net tonnage (15.2 and 14.3) on it. Maybe should not show them that, although if I remember it is also on the DEKRA. Just noted no tonnage on the SSR - I was mistaking the need to state it with the VHF licence for a UK boat which does require you to state Gross Tonnage - I am told because it gives an indication of size for recognition!