Entry & progression
Every threshold in this course is written in tons. 200 GRT. 500 GRT. 1,600 GRT. And the number the yacht industry quotes is measured on a different system. Confuse the two and every conclusion you draw is unsafe.
The two systems
| System | Where it comes from | Where you meet it |
|---|---|---|
| Regulatory tonnage — GRT | 46 U.S.C. chapter 145 | The US thresholds: 200 GRT, 500 GRT, 1,600 GRT |
| Convention / ITC tonnage — GT | 46 U.S.C. chapter 143 | The brochure, the charter listing, the international conventions |
The thresholds that decide whether a vessel needs an engineer, and the caps that limit the Designated Duty Engineer and the Limited grades, are Regulatory tonnage. The number a broker, a shipyard or a crew agent quotes you is almost always ITC.
WARNING — A yacht marketed as '499 GT' is quoting ITC That famous number is a Convention measurement, chosen because 500 GT is where a raft of international obligations begins. It is not her regulatory tonnage. Her GRT is a different number, arrived at by a different rule.
We are not going to tell you how big the gap is. The magnitude of the difference between GRT and ITC for a typical yacht could not be established from primary sources, and inventing a rule of thumb here would be worse than useless — people would plan careers on it. Do not estimate. Measure.
What to do instead of estimating
Go to the paperwork. The vessel's Certificate of Documentation carries her tonnage as the United States measures it. That is the number that speaks to 200 GRT, 500 GRT and 1,600 GRT. Test the threshold against the certificate, not against the brochure.
How the CFR credits tonnage on your sea service
Two rules govern what tonnage goes on your service record, and they pull in opposite directions — so read them together:
- 46 CFR 11.211(h) — a vessel measured solely under the Convention system has her tonnage credited as GRT. If there is only one number, that number is used.
- 46 CFR 11.301(b)(4) — a dual-tonnage vessel is credited at the international tonnage. Where both numbers exist, the ITC figure is the one that counts.
So on the service-crediting side, the international figure often carries the day. That does not make GRT and GT the same thing — it means the CFR has told you which of two different numbers to use, in two specific situations. Everywhere else the distinction stands.
NOTE — Why this lesson exists at all Because almost every wrong conclusion in the previous module starts here. "She's 480 tons, so she's under 500 — DDE covers it." Under 500 what? If the 480 came from a charter listing it is an ITC figure and it has not answered the question the CFR asked. The tonnage cap on every Designated Duty Engineer endorsement is less than 500 GRT, and the Limited grades sit at less than 1,600 GRT on ocean and near-coastal routes. Those are regulatory tons.
CAUTION — There is a genuine conflict inside the CFR here — do not paper over it 46 CFR 11.501(b) caps the Limited grades at less than 1,600 GRT on the Great Lakes, while 11.323(d) speaks of less than 3,000 GT in Great Lakes service. The two numbers genuinely conflict, and this course is not going to pick one for you. If your plan turns on Great Lakes tonnage, put the question to the NMC in writing.