Short answer: “Boat” is the everyday word for a small watercraft. “Yacht” describes how a vessel is used: for pleasure, privately or on charter, at almost any size. “Ship” usually means a large seagoing vessel built for trade, passengers or state service. A large yacht can legally be a ship; the difference is purpose, not size. No single international size makes a boat a ship. Maritime rules switch on at specific thresholds of length, gross tonnage and passenger numbers, and many of them depend on whether the vessel is used commercially.
The three words are often mixed up, and in conversation that rarely matters. In a sale contract, an insurance proposal or a refit specification it does, because the rules a vessel must meet follow its size and its use, not the name people give it.
Yacht vs Boat vs Ship at a Glance
A boat is a small craft, a yacht is a vessel used for pleasure, and a ship is a large seagoing vessel for trade or state service. The table compares them side by side. GT stands for gross tonnage, a measure of enclosed volume.
| Boat | Yacht | Ship | |
|---|---|---|---|
| What the word signals | A small watercraft, used for almost anything | A vessel used for pleasure: private use or charter | A large seagoing vessel for cargo, passengers or state service |
| Typical size (informal) | Small. In the EU, “recreational craft” means 2.5 to 24 m hull length | From around 10 m to over 100 m. “Superyacht” usually means about 24 m and above | Usually tens to hundreds of metres |
| Who runs it | Usually the owner | The owner on smaller yachts. Professional crew on most larger yachts | Certificated professional crew |
| Main rulebooks | National small-craft rules, COLREG at sea, EU RCD for design and build | COLREG, MARPOL and parts of SOLAS Chapter V for all. Commercial yachts add yacht codes, Load Line, STCW, MLC and, from 500 GT, the ISM Code | Applicable conventions depend on vessel type, use, size and voyage: SOLAS, MARPOL, Load Line, STCW, ISM, MLC |
| Example | Fishing boat, RIB, day cruiser, dinghy | Motor yacht, sailing yacht, explorer yacht | Container ship, tanker, cruise ship, frigate |
The table describes common usage. In law, the lines are drawn differently, as the next section shows.
When Does a Boat Become a Ship?
There is no single size at which a boat becomes a ship. The answer depends on which rulebook you are reading. In practice, the thresholds that matter most are more than 12 passengers, 24 m load line length, and 300, 400 and 500 GT. Three points explain why.
1. Legal definitions of “ship” are broad. Many laws do not use size at all. Under the UK Merchant Shipping Act 1995, “ship” includes every description of vessel used in navigation, so for that Act a yacht is a ship. MARPOL defines a ship as a vessel of any type operating in the marine environment. COLREG, the collision regulations, uses the word “vessel” for every kind of watercraft, from a dinghy to a supertanker.
Illustration: a container ship. Every legal definition treats a vessel like this as a ship.
2. Rules switch on at thresholds. International conventions apply from specific measurements. Gross tonnage (GT) measures a vessel’s enclosed volume, not its weight. Length also comes in several forms, such as LOA and load line length, so always check which one a rule uses. The most common thresholds are:
| Threshold | What changes | Source |
|---|---|---|
| More than 12 passengers | The vessel is defined as a passenger ship under SOLAS. The definition alone does not decide which SOLAS rules apply or which exemptions are available | SOLAS Reg. I/2 |
| 24 m load line length | On international voyages, the Load Line Convention covers new ships of 24 m and over and existing ships of 150 GT and over. Pleasure yachts not engaged in trade are excluded. The REG Yacht Code Part A also starts at 24 m, for commercial yachts carrying no cargo and no more than 12 passengers | Load Line Convention, Art. 4-5; REG Yacht Code Part A |
| 300 GT | SOLAS radio rules (Chapter IV) apply to cargo ships on international voyages. Since 1 January 2026, private yachts of 300 GT and above in polar waters must meet certain Polar Code navigation and voyage-planning rules | SOLAS IV; SOLAS XIV |
| 400 GT | MARPOL sewage rules (Annex IV) cover ships on international voyages of 400 GT and above, or certified to carry more than 15 persons. The air pollution (IAPP) and sewage (ISPP) certificates have additional voyage conditions | MARPOL Annex IV and VI |
| 500 GT | On international voyages, most SOLAS chapters apply to cargo ships of 500 GT and above, and the ISM Code applies to them as well as to all passenger ships. A commercial yacht carrying no more than 12 passengers counts as a cargo ship here | SOLAS; SOLAS IX / ISM Code |
3. Use matters as much as size. SOLAS, the Load Line Convention and STCW each exclude pleasure yachts not engaged in trade, although some SOLAS navigation rules still apply to them. The Maritime Labour Convention (MLC) applies to ships ordinarily engaged in commercial activities. So a large private yacht can sit outside several conventions that a smaller charter yacht has to meet.
Sailors have an old rule of thumb: a ship can carry a boat, but a boat cannot carry a ship. The saying is useful, but it is a tradition, not a legal test.
What Is the Difference Between a Boat and a Yacht?
The difference is purpose, not a legal size. Every yacht is a boat, or at larger sizes a ship. “Yacht” usually signals pleasure use, often with overnight accommodation and more complex systems. No international rule sets a minimum length for a yacht.
Illustration: a RIB (rigid inflatable boat). Most people would call this a boat, not a yacht.
“Superyacht” is an industry label, usually used for yachts of about 24 m (79 ft) and above. It has no single legal definition. The 24 m mark matches the length at which load line rules and large yacht codes start, and the upper limit of the EU’s recreational craft rules. Read more in What is a Superyacht? and Types of Yachts Explained, or see the glossary entries for motor yacht, sailing yacht, explorer yacht and megayacht.
What Is the Difference Between a Yacht and a Ship?
A large yacht can legally be a ship. The real difference is function. A ship is built to carry cargo or passengers for trade, or to serve a state, such as a warship or research vessel. A yacht is built for pleasure, private or on charter.
Illustration: a motor superyacht. At this size it can legally be a ship, but it is built and used for pleasure.
At the top of the market the two worlds meet. Large yachts are built in steel or aluminium to rules set by classification societies. Commercial yachts of 500 GT and above on international voyages run an ISM Code safety management system, as merchant ships do. Yachts carrying 13 to 36 passengers fall outside the normal large yacht codes. Under Red Ensign flags they can be certified under REG Yacht Code Part B, the passenger yacht code, which covers international voyages without cargo and caps the total number of persons on board at 200. Other flags apply SOLAS passenger ship rules or their own equivalents.
Private vs Commercial: The Line That Matters Most for Yachts
For yachts, the private versus commercial question often matters more than length. A yacht used only by its owner is a “pleasure yacht not engaged in trade”. A yacht offered for charter is engaged in trade, and the rulebook changes.
| Rule | Private yacht (not engaged in trade) | Commercial yacht (charter) |
|---|---|---|
| SOLAS | Most chapters do not apply. Chapter V (safety of navigation) applies in part, though flags may exempt smaller vessels from some rules. Since 2026, certain polar navigation rules apply from 300 GT | Applies by size and voyage, usually through the flag’s yacht code |
| Load Line | Excluded | Applies on international voyages from 24 m (new ships) |
| STCW | Excluded | Crew need STCW-based certificates; flags issue yacht-specific ones |
| MLC | Outside scope | Applies to crew working conditions |
| ISM Code | Not required by SOLAS Chapter IX; flag rules may differ | Mandatory from 500 GT on international voyages |
| MARPOL | Applies, for example the garbage rules in Annex V | Applies |
| COLREG | Applies | Applies |
Flag state rules sit on top of all of this and differ between flags. Older yacht codes such as LY3 have now been replaced by the REG Yacht Code for Red Ensign flags.
Design, Build and Maintenance
Boats are built simply, yachts are built for comfort and range, and ships are built for continuous work:
- Boats: usually GRP (fibreglass), aluminium or wood, simple systems, often stored ashore or on a trailer.
- Yachts: GRP, aluminium or steel, from series production to fully custom builds, with complex accommodation, navigation and engineering systems.
- Ships: steel, built for durability and continuous operation, with redundant systems.
Larger yachts follow a ship-like maintenance cycle: periodic haul-outs or dry docking, antifouling, and class and flag surveys. Bigger work happens in a planned yacht refit.
Which Word Should You Use?
Use the word that matches the vessel’s use, and in formal documents describe the vessel by its facts:
- Use boat for small craft and in everyday speech.
- Use yacht for vessels used for pleasure, whether private or on charter.
- Use ship for large commercial, passenger or state vessels.
In contracts, insurance and compliance documents, do not rely on the word alone. State the vessel’s length (and whether it is LOA, hull length or load line length), gross tonnage, flag, passenger capacity and whether it is used privately or commercially. These facts decide which rules apply. Misdescribing a vessel’s use, for example declaring private use while chartering, can raise questions about insurance cover and compliance.
Frequently Asked Questions
Is a yacht a boat or a ship?
Both, depending on size and context. In everyday speech a yacht is a type of boat. In many laws, such as the UK Merchant Shipping Act 1995 and MARPOL, a yacht counts as a ship whatever its size.
At what size does a boat become a ship?
There is no single size. Rules apply from different thresholds: more than 12 passengers (SOLAS passenger ship), 24 m load line length (Load Line Convention and large yacht codes), and 300, 400 and 500 GT for different SOLAS, MARPOL and ISM requirements.
Is 500 GT the line between a yacht and a ship?
No. 500 GT is the threshold at which most SOLAS chapters and the ISM Code apply to cargo ships, including commercial yachts, on international voyages. It does not turn a yacht into a ship, and a private yacht of any tonnage stays a pleasure yacht.
Is a 100 ft yacht a ship?
It can be in law, because many legal definitions of “ship” cover any vessel used in navigation. In everyday use it is called a yacht. At about 30 m, it is above the 24 m mark where large yacht codes start, so if it is chartered, a commercial yacht code usually applies, depending on the flag.
What size is a superyacht?
Usually about 24 m (79 ft) and above. This is an industry convention, not a legal definition, and terms such as megayacht have no agreed threshold.
Do yachts need a licensed crew?
It depends on use and flag. Commercial yachts need crew with STCW-based certificates. For private yachts, requirements depend on the flag state and the size of the yacht, so check the flag’s rules.
Are ships always used commercially?
No. Warships, research vessels and other government ships are ships but are not used for trade. Many conventions treat them separately.
What is gross tonnage?
Gross tonnage is a measure of a vessel’s total enclosed volume, calculated under the 1969 Tonnage Convention. It is not a weight. See Gross Tonnage (GT).
Sources
- UK Merchant Shipping Act 1995, section 313
- IMO: MARPOL and Annex V garbage rules
- IMO: COLREG
- IMO: Load Lines
- IMO: ISM Code
- IMO: Polar Code
- IMO: Tonnage Convention
- EU Recreational Craft Directive 2013/53/EU
- Red Ensign Group Yacht Code, Part A (July 2024 edition) and Part B (July 2024 edition)
- ILO: Maritime Labour Convention, 2006
