Official rule text as published in the U.S. Coast Guard Navigation Rules
For the purpose of these Rules, except where the context otherwise requires:
(a) The word "vessel" includes every description of watercraft, including non-displacement craft, WIG craft, and seaplanes, used or capable of being used as a means of transportation on water.
MyCOLREGS explanation
Summary
Rule 3 defines the vocabulary the rest of the Rules run on, and the definition of "vessel" itself is broad by design: any kind of watercraft — including non-displacement craft, Wing-In-Ground craft, and seaplanes — counts as a vessel if it is used, or capable of being used, to get around on the water. That breadth matters because paddleboards, personal watercraft, and unconventional craft do not get to opt out of the Rules just because they do not look like a traditional boat.
Real World Example
That breadth is not academic: the moment a jet ski, an inflatable, or an oddball non-displacement craft is capable of being used to get around on the water, its operator owes the same collision-avoidance duties as the captain of a cargo ship, just scaled to her size.
Practice Questions
Q1. A paddleboarder is capable of using the board as a means of transportation on water. Based on Rule 3(a), is the paddleboard a "vessel" under the Rules?
A. Yes — Rule 3(a) defines "vessel" broadly as every description of watercraft used or capable of being used for transportation on water, including non-displacement craft.
B. No — only commercially registered craft count as vessels, since Rule 3(a)'s definition was intended to regulate documented vessels engaged in trade, not recreational equipment.
C. No — only vessels with an engine or sail count as vessels, since Rule 3(a) was written before human-powered watercraft like paddleboards existed.
D. It depends on the paddleboard's length in meters, since Rule 3(a)'s vessel definition uses the same length brackets found elsewhere in the Rules.
Q2. A hydrofoil lifts her hull entirely clear of the water once she's up to speed, riding on submerged foils rather than displacing water like an ordinary hull. Under Rule 3(a), does that make her something other than a "vessel"?
A. No - Rule 3(a) specifically includes non-displacement craft within the "vessel" definition, so riding up out of the water doesn't remove her from the Rules.
B. Yes - only vessels that displace water at all times qualify as "vessels" under Rule 3(a), since the drafters intended the term to track a craft's normal hull-in-the-water operating mode.
C. It depends on her top speed; craft capable of exceeding 30 knots are reclassified outside the vessel definition and governed instead by separate high-speed-craft regulations.
D. Yes, but only while she is foiling; she becomes a vessel again the moment she settles back onto her hull and starts displacing water in the ordinary way.
Practice Question Answers
Q1.
A. Yes — Rule 3(a) defines "vessel" broadly as every description of watercraft used or capable of being used for transportation on water, including non-displacement craft. Rule 3(a)'s definition is intentionally broad, covering every description of watercraft — including non-displacement craft, WIG craft, and seaplanes — used or capable of being used for water transportation. B, C, and D each try to narrow "vessel" down to a stricter category - registered, powered, or size-based - but Rule 3(a)'s definition is deliberately broad: anything capable of transportation on water.
Q2.
A. Non-displacement/WIG craft and seaplanes. Rule 3(a) names WIG (Wing-In-Ground) craft and seaplanes explicitly, in addition to the general non-displacement craft language, making clear the definition reaches well beyond conventional hulls. A, C, and D each name a plausible-sounding craft, but Rule 3(a) specifically calls out non-displacement craft, WIG craft, and seaplanes - not jet skis, amphibious vehicles, or submarines.