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When Does a Boat Become a Ship? – Difference Between a Ship & a Boat

Written by J. Harvey / Fact checked by S. Numbers

when does a boat become a ship

When does a boat become a ship? It’s all about the size. In simple terms, a boat becomes a ship once it exceeds a length of 100 feet or if a vessel can fit another boat.

There are other factors that may differentiate the two, though, like areas of operation, navigational and sailing technology used, heel direction when turning, and what powers and propels a vessel. That being said, there’s really no universally agreed-upon distinction.

Differing Definitions And The Variety Of Watercrafts Now Available Make Distinguishing Tricky


In my research, besides the two have been mentioned above, I’ve come up with this list, which is what people and nautical organizations have come up with to differentiate a boat from a ship:

  • It has to have at least three masts and all of them have to be square-rigged. This definition can be difficult to apply to plenty of modern-day vessels, though.
  • It has to have multiple decks. You’ll notice that most vessels with two or more full-length decks above the waterline are normally large and are called ships.
  • It has to be able to carry and transport boats. Nonetheless, this disregards vessels that are large enough to transport the biggest ships out there. The best example of this is the Blue Marlin, a type of semi-submersible, heavy-lifting ship that can even hold battleships and medium-sized cargo ships.

While we did say that size is a big thing when distinguishing a boat from a ship, did you know that submarines are generally referred to as the former? The Grey Funnel says that’s the case because, in the early days of submarining, these vessels were tiny enough to be launched and retrieved from so-called “tenders” or ships. Submarines also noticeably have only one deck above the waterline.

Still, their modern incarnations aren’t exactly small, right? The same goes for some yachts, which are generally considered as sizable luxury boats. Even so, if I’m going to use the 100-feet rule when answering “how big does a boat have to be to be considered a ship”, the world’s largest yacht becomes a ship because it’s close to 600 feet in size!

The Two Are Arguably Almost Synonymous With Each Other

At least, I can say as much when I look at how 19th century maritime law regarded the two as belonging to only one legal category. This obviously goes against the size definition.

The everyday phrases we use don’t help, either. For instance, do we say “abandon boat” instead of “abandon ship” regardless of whatever size vessel we’re currently riding? Also, what do we say when we’re leaving port? We’re “shipping out”, even if we’re just riding a 20-footer or even a small fishing boat, right?

Other Factors That Help In Telling Vessels Apart


According to more technical marine knowledge, here are a couple of factors that effectively determine at what point does a boat become a ship. Most of them are qualities and capabilities unique to either one.

  • The direction that the vessel heels toward when making a sharp turn may also be a telling sign. Smaller watercraft tend to heel or lean toward the inside of the turning circle, while ships are the opposite and will lean toward the outside. In most marine circles, this is generally considered the best way to tell these two apart.
  • As long as a vessel has enough loading capacity to carry numerous goods at sea, it can already be considered a ship. In countries like India, this is actually a legal definition.
  • When it comes to navigating the high seas and oceans, ships are often the vessel of choice. Cargo and passenger ships, naval ships, and tankers normally populate these areas. On the other hand, kayaks, sailboats, and canoes are often limited to smaller water areas.
  • While some boats may use more advanced navigational and sailing equipment and technology, they don’t compare to ships that are rigged with more heavy-duty machinery and sophisticated navigational systems.
  • A ship will typically require a high-capacity engine to propel it forward, while a boat will only need a motor or can even be rowed manually if need be.

So What’s The Best Definition

To me, it’s best to stick to the size-based definition. I say this because that’s what the majority of people and organizations agree on. I can say the same for the direction of the vessel when turning.

Ultimately, there are numerous factors and definitions to consider, to the point that it’s best to just pick the one that you find the most acceptable.


So to sum everything up, when does a boat become a ship? You’ll have to consider the size, manner of operation, and the host of other factors I’ve mentioned here in order to truly see the difference. What’s good is that there’s really nothing wrong in mistaking one for the other, especially if we look at the whole nautical picture and regard what these vessels can and can’t do and how sailors use them.

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