Looking to upgrade to CM unlimited, question about GT vs GRT. Seatime is on OSVs and my seatime letter is all written in GT, smallest being 2994 GT. I understand 50 percent of sea-time must be over 1600GRT but how would that work if seatime is all written in GT? The vessel COI’s also are written in GT only.

Thank you kindly

I don’t think the NMC (or at least the evaluators) see a difference between GT and GRT. I never had an issue upgrading with GT sea time letters from OSVs.

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jdcavoTop Contributer

Dec '13

Probably not. Generally, GT is higher than GRT. The difference is that GRT excludes certain spaces from the volume calculation that GT does not. This is why it’s vessel specific and there is no conversion formula, ikt depends on how many of those GRT excluded spaces are on the vessel. For mariner credntial putrposes, the Coast GHuard has considered 200 GRT to be equivalent to 500 GT and 1,600 GRT to be equivalent to 3,000 GT. These are the only two such equivalencies, we do not interpolate a linear relationship between these two points.

An overly simple way to think of GRT vs. GT is to consider a filing cabinet 3.5’ x 3.5’’ x 3.5’. Is there any way to get that through a door that is 3’ wide? Under GRT, you could if you took the drawers out.

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See 46 CFR 11.211(h).
Note that this regulation is from after the 10+ year old post quoted above.

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3000GT is usually considered equivalent to 1600GRT

It’s pretty wild you’re just 6 GT shy of that requirement, I wonder what the Coast Guard will say to that. They will probably be sticklers. At the same time it’s probably fairy dusted magically just under 3000GT to avoid extra regulation. Read about the story of the yacht Limitless and other large yachts. Often they will get engineers to fib the number because it’s cheaper than the alternatives.

I met a hawsepiper once who worked on an OSV for all his time that was literally 1 ton greater than he needed for unlimited(grt or gt I don’t remember), but he said he had to fight tooth and nail just to get them to accept that. It’s an anecdotal story, but I believe it

There is absolutely a huge difference. ITC’s GT is often a much higher number. It doesn’t matter as long as the numbers correspond somewhat to their appropriate ratio ie 5000GT is still unlimited just as 2000GRT is (made up numbers)

In the USA they can take a 3000grt vessel and make it a 90 grt
I would think any exam question is about what how you do that?

If worse comes to worse, wouldn’t you be approved for a chief mate w/a tonnage limitation of some sort i.e. 2000 grt?

I have enough well over the 3,000 GT mark so shouldn’t be an issue.

I even have some 2 GT under the 3k mark, I’m curious what they would say as well. I guess it would vary evaluator to evaluator but rules are rules, not much to argue if they were to slap a tonnage restriction on it for someone who would be put in that situation.

GT vs GRT:

Source: Gross register tonnage - Wikipedia

Maybe time to get with the rest of the world to avoid confusion?


Thank you!

I understand the NMC has extended the deadline for QA, so per CFR 46 10.405(a)(3) if the master of the vessel is signing off assessments in NVIC 10-14( mngmnt 3000 or more) does their OSV or 6,000/10,000 ITC endorsement suffice paragraph 3? Qualification equal or superior….

(3) Possession of the level of endorsement, or other professional credential, which provides proof that he or she has attained a level of experience and qualification equal or superior to the relevant level of knowledge, skills, and abilities to be assessed.

Applying to add chief mate and then master eventually w/ no restrictions to STCW but am concerned that a master OSV or 10000itc is signing off my assessments.

I understand these need to be signed off on a vessel over 3,000 GT which isn’t an issue but just concerned about the actual person signing.