46 CFR § 69.71 - Change of net tonnage.
(b) A vessel concurrently assigned load lines under both the International Convention on Load Lines and either the International Convention for the Safety of Life at Sea (SOLAS) or other international agreement must be assigned only one net tonnage. The net tonnage assigned must be the net tonnage applicable to the load line assigned under the International Convention on Load Lines, SOLAS or other international agreement for the trade in which the vessel in engaged.
(c) When a vessel is altered so that the net tonnage is decreased or the vessel's trade is changed so that the load line assigned for that trade under paragraph (b) of this section is no longer appropriate and results in a decrease in its net tonnage, a new International Tonnage Certificate (1969) incorporating that net tonnage may not be issued until twelve months after the date on which the current Certificate was issued. However, if one of the following apply, a new Certificate may be issued immediately:
(1) The vessel is transferred to the flag of another nation.
(2) The vessel undergoes alterations or modifications which the Commandant deems to be of a major character, such as the removal of a superstructure which requires an alteration of the assigned load line.
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