Agreed. But a domestic tonnage limitation would not apply if the vessel is operating under the STCW scheme.
An STCW endorsement without any limit written directly on it isn’t the same as a license without a limit. The domestic is your license and the STCW section just says you meet certain STCW standards as well. They are not separate licenses and you’re always subject to any restrictions on your domestic license.
I never said it was. It depends on the restriction you are talking about. In this case, a restriction on domestic tonnage (GRT) means absolutely nothing and does not apply if the vessel is sailing under the STCW scheme (GT).
And you are also subject to any restrictions on your international endorsements. But not “always” for either domestic or international. Again, see 46 CFR 15.401(f).
Whether or not a vessel is sailing on GRT or GT has nothing to do with whether it is required to follow STCW.
Is it possible for a vessel sailing STCW (on an international voyage) to sail without having a tonnage certificate giving an admeasurement in ITC? I don’t know the answer to this, but I don’t think so:
§69.69 Tonnage certificates.
(a) On request of the vessel owner, the authorized measurement organization must issue an International Tonnage Certificate (1969) as evidence of the vessel’s measurement under this subpart for a vessel that is 24 meters (79.0 feet) or more in registered length, will engage on a foreign voyage, and is not a vessel of war. The Certificate is delivered to the vessel owner or master and must be maintained on board the vessel when it is engaged on a foreign voyage.
Then there is also the question of what happens when a vessel not required to have STCW has only ITC and not domestic tonnage measurement. That is what started this whole thread.
Edit: My point is that GRT is meaningless on international voyages and that is why any restrictions on GRT from your national endorsement don’t apply.
Those aren’t the only times a vessel is required to follow STCW. A non exempt seagoing vessel is required to follow STCW at all times, even if they’re just moving within inland waters.