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Old 25th March 2011, 12:12 AM
landbound landbound is offline
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Default Calculation of GT (Gross Tonnage) Help Needed

Can anyone assist with regard to the measurement of GT (Gross Tonnage) for a catamaran sailing boat of approximately 14 Meters

I do understand that most boating countries have a simplified calculation applicable to pleasure boats and in the case of the USA for craft below 5GT. This is not the case for Indonesia where the measurement is required.

I want to own and sail a catamaran in Indonesia. The Indonesian shipping Law 17 / 2008 is clear that only an Indonesian may own or sail a boat avove 7GT. Thus any boat I build or buy must be below 7GT. I am fully aware of the CAIT that permits foreign flagged vessels to cruise Indonesia, however I am not looking for avoidance strategies however useful they have been for others.

Anyone with a knowledge of International Convention on Tonnage Measurement of Ships, 1969 will realize it is purposed for cargo ships and to a lesser extent for passenger ships not for pleasure craft - thus an enthusiastic amateur is unlikely to get any calculation right, - not because the calculations are difficult but becuase the defintions are really unsuitable for catamarans - the full horror of the measurement methodology can be viewed here -

I am delighted to pay a professional to perform the calculations and would supply cad drawings that would allow the determination of internal volumes. That person must be "a competent person or organization recognized under the provisions of the international treaty" my guess is if you don't know if you are then you are not !

For me to engage such a person I would want evidence that they are authorized to certify by their relevant national authority and that they have some experience calculating GT on pleasure craft using the full treaty method not for example the US Coast Guard "simplified" calculation. With the greatest respect to any marine surveyor reading this, years of experience with tankers and bulk ore carriers is unlikely to be helpful. What will help is practical experience with the relevant authorities and knowing for example what the authorities view of the definition of a "deck" or "stepped deck" is with respect to a sailing catamaran.

Equally welcome would be a contact that you know might be versed in such arcana.

If you have managed to get to the end of this incredibly dull email I thank you and ask you to shed a tear for those who wish to sail legally in Indonesia without resorting to classic third world "fixes".

Guy Warwick
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Old 8th April 2011, 07:24 PM
Catkid Catkid is offline
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Default Re: Calculation of GT (Gross Tonnage) Help Needed

just learned this today from uscg while renewing my master ticket:

length x width x draft X .67 divided by 100
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Old 8th April 2011, 08:50 PM
dmmbruce dmmbruce is offline
Boat: 26 ft Heavenly Twin - TWO MINDS
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Location: Stratford upon Avon, boat Poole
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Default Re: Calculation of GT (Gross Tonnage) Help Needed

Landbound, you don't do yourself justice. Your post was beautifully clear and lucid. I found it interesting from a distant perspective!

Have you tried asking locally. For example Harbour Masters are often a source of information, or the secretary of any sailing clubs or similar associations. Perhaps a local boatyard. Those who are in the area are the most likely to know. Or ask the Licensing Authority to point you to someone who can do it or knows where to get it done.

I suspect you have already tried all these sources, but maybe it may help.

Good luck.

Wrong no man, write no woman.
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Old 9th April 2011, 12:14 AM
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Default Re: Calculation of GT (Gross Tonnage) Help Needed
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