Does the vessel have both a domestic and and international tonnage certificate?
If the office is saying it’s 1691 GT (ITC), but it’s dually documented and has a GRT under 1600, there in lies your problem from what I’ve read.
Policy Letter 11-12 refers only to vessels measured in both conventional and regulatory measurement systems i.e., Dual Tonnage.
● It applies to vessels that have both measurements, Gross Registered Tons (GRT) & Gross Tons (International Tonnage Convention) [GT (ITC)], in Marine Information for Safety and Law Enforcement (MISLE)-
200 GRT = 500 GT (ITC)
1600 GRT = 3,000 GT (ITC)
If a vessel only has ITC tonnage, then the ITC tonnage will be credited as Gross Registered Tons and the guidance in this policy letter would not apply. (In other words, vessel tonnage is listed as 2300 ITC and has no GRT listed, then the mariner would be credited with service on a vessel of 2300 GRT.)