Gross tonnage - comparing ship sizes !

[libertyshiplad]

Looking at various websites gross registered tonnage measurement applied to ships built before 1982,such ships for commercial reasons retained this measurement until 1994 when new measurement rules of gross tonnage would apply.
I think I am right in that after 1994, gt for these ships built before 1982,as shown on Shipspotting,in indexes & journals etc always related to their original grt whe built?
The changes in measurement it seems had a big effect on certain vessels - car carriers,ro-ros & ships with open shelterdecks,greatly increasing their gt.
I believe a lot of the older freighters with tonnage hatches,depending on their voyage & cargoes could then operate as open shelterdeckers with a significant reduction in their grt resulting in lower fees & charges.I assume  gt now shown would always be for the ship operating as a closed shelterdeck vessel with its original grt given.
Sorry if this is a bit rambling,but what I would like to know is,that for the vast majority of ships built before 1982,their gt as shown on Shipspotting etc would be very similar to gt as measured under the new rules (very little difference).
Would the gt of the largest container ships around now be similar if measured under the old grt measurement?
Would the gt of a liberty ship measured under the new rules be much different?

[libertyshiplad]

Thanks Ken,did come across that interesting article.
Doesn't quite answer my question,with ship photos or articles often just year of build and gt given.
Best regards,
Colin

[Phil English]

The 1969 International Convention on Tonnage Measurement of Ships, came into force in 1982. With few exceptions all operating vessels irrespective of age were required to be re-measured in accordance with the new rules. A full explanation of how those rules were applied can be found here:

https://www.uscg.mil/hq/msc/tonnage/docs/TM_Convention_Draft_Text_Version_With_Figures.pdf

Brgds
Phil

[libertyshiplad]

Thanks Phil,did come across that article too.
I suppose ,thinking about the last 3 paragraphs of my original post,there has never been the need to do these advanced mathematical calculations ,so maybe answers are at present unknown?
Would have liked to have known the answers though!
Regards
Colin