I have a general understanding of how GT and GRT are calculated but not exactly clear on how it relates to licensing.  Quick back story:  I have a 100 ton/near coastal license and ran a boat in summer of '15, private use only, that was 109 gt.  The owner wanted to charter it so obviously I could not run it for hire.  It was incredibly frustrating for the owner and myself because I was covered by the insurance as captain for private use only.  And at the time I was eligible for upgrade to 150ton only to discover the USCG eliminated it and currently I do not have the time for 200ton upgrade.

Back to my original point;  Does GRT override GT in terms of operation and/or vessel capacity in an effort to help guys like me?

...........Bueller?

GRT does not override GT, it is a much more complicated situation than you make it sound. For the purpose of safety and manning requirements, your license GRT limitations must be greater than the vessel’s GRT measurement.
GRT does not equal GT. One does not override the other, they are simply not compatible. Your license is limited to GRT. They are two completely different measurements that are derived from different formulas. The basic idea of internal measurement is similar for both but one is not like the other and they are sometimes incorrectly used interchangeably. Do not go to Wikipedia for info on GT vs GRT because it’s not very accurate. At all.

If the vessel has a GT but not a GRT and you need to determine if your license is sufficient to operate the vessel then you would need to perform the calculation to determine your vessel’s actual GRT measurement. The USCG has an entire form you use to calculate the GRT. Search the USCG.mil site for “TG 1 CH-2“ OR I guess you could just click on this link https://www.dco.uscg.mil/Portals/9/DCO%20Documents/Marine%20Safety%20Center/Tonnage/Tonnage%20Guide%201%20-%20Simplified%20Measurement.pdf

You may find that your license works for this particular vessel, or maybe you won’t. It’s also possible that someone calculated GRT a and mistakenly labeled it as GT but you’ll never know until you calculate the actual GRT value of the vessel. Wish I could help make it easier for you

thanks otterbox. i've actually been researching this topic and i have discovered that GT is the standard dimension calculation which applies to all vessels, domestic and foreign. GRT is a US domestic calculation for passenger vessels operating under subchapters T, K, etc., and focuses on the ratio of operational spaces to passenger spaces. Builders can design and build massive dinner cruisers upwards of 200' long under 100 GRT so companies can hire 100ton captains.

Chuck, that is exactly right. GRT is a US-based system of measurement for the purpose of determining manning requirements. For the purpose of construction, GT is used.