Entry & progression
46 CFR 10.107: propulsion power "excludes thrusters and other auxiliary machinery." Your gensets do not count. Your bow thruster does not count. A large, expensive yacht can sit below 3,000 kW — and that changes which certificate she needs.
The definition, verbatim
10.107: "Propulsion power means the total maximum continuous-rated output power of the main propulsion machinery of a vessel determined by the manufacturer, in either kilowatts or horsepower, which appears on the ship's Certificate of Registry or other official document and excludes thrusters and other auxiliary machinery."
Read the exclusion again. Then go and look at a yacht. She has two bow thrusters, a stern thruster, three or four generators sized for a hotel load that would embarrass a small ship, hydraulic power packs for the passerelle and the crane, and — behind all of it — two main engines that are, by ship standards, quite modest.
WARNING — The auxiliaries are the impressive part and none of it counts Only the main propulsion machinery counts. A 60-metre yacht whose mains total 2,600 kW is, for the purposes of 46 CFR Part 11 Subpart C, a 750–3,000 kW vessel — however much installed power she carries elsewhere, and whatever her gross tonnage says.
The certificate she needs is III/3 (11.331 / 11.333), not III/2. The chief of that boat is still a management-level officer. She simply sits in the lower band.
And 11.503(a) says the same thing from the other side
"The propulsion power limitation... is based on the applicant's qualifying experience considering the total shaft propulsion power of each vessel on which the applicant has served." Shaft propulsion power. The Coast Guard is counting what turns the propellers.
So the exclusion cuts both ways, and the second cut is the one that hurts. A career spent on beautiful boats with small mains builds a low horsepower endorsement — and Lesson 2.3 told you what a low horsepower endorsement does to the III/2. The yacht that is smaller than she looks does not just need a smaller certificate. She builds one.
CAUTION — Diesel-electric, hybrid and unconventional plants — ask, do not assume On a diesel-electric yacht the generators are the source of propulsion. Where the line between 'main propulsion machinery' and 'auxiliary machinery' falls on such a plant is not something this course will guess at, and the fact base does not settle it.
The definition points at the figure that "appears on the ship's Certificate of Registry or other official document." Start there — and put the question to the National Maritime Center in writing before you count a single day of service. Getting this wrong costs years.
Two more numbers that are not what they look like
- GRT is not GT. The US thresholds (200 GRT, 500 GRT, 1,600 GRT) are Regulatory tonnage. The yacht world quotes ITC / Convention tonnage. A yacht marketed as 499 GT is quoting ITC; her regulatory tonnage is a different, usually lower, number. Never equate them — and do not let anyone tell you the size of the gap, because it varies.
- When STCW attaches — 15.1103(a). On a seagoing vessel of 500 GT or more driven by machinery of 1,000 HP / 750 kW or more, or on an international voyage beyond the boundary line, no person may serve in a position requiring an STCW endorsement without holding one. Seagoing is defined at 10.107 as operating beyond the boundary line — a geography test, not a size test.
Know your boat's real numbers. Not the brochure's. The propulsion power on the certificate of registry is the number your career is measured in.