Ship versus boat

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Every now and then you'll hear someone nag about that something is a ship, not a boat.

I wanted to know.

Turns out it's one of those rule-of-thumb-with-fuzziness-and-exceptions things.

The simplest answer is that it's about size

Everything small - rubber boats, canoos, rowboats, lifeboats - are boats by any definition.

Pretty much everything huge is a ship, by most definitions and by most pragmatics.

It's more shippy if

it has a captain

it can carry a boat, e.g. a lifeboat

it has multiple decks

larger:

in sailing, one definition of a ship a "square-rigged craft with at least three masts, and a boat isn't" (where square-rigged basically means multiple sails per mast)

large and motorized: "a ship is a large vessel intended for oceangoing or deep-water transport, and a boat is anything else"

It's more boaty if

it couldn't carry a boat(/ship)

it has just one deck

For things inbetween, a good rule of thumb is that

It's easily a ship if it can carry a boat, e.g. a lifeboat, while

a boat cannot carry a ship.

and yet there are still exceptions, including:

• submarines are considered boats, apparently on account of the single deck of the first generations of their designs, even though there are now many variants with more than one deck

yet e.g. the US typically calls USS Something, where USS means United States Ship.

but not everyone agrees on this one in the first place

• ferries are considered boats, even though they typically have lifeboats, and now typically have multiple decks

this may be because the first ferries were tiny things like cable ferries which were barely more than rafts.

• commercial fishing craft are typically large enough to be safe on a wilder sea, and carry lifeboats, but are typically called boats (perhaps because of the large main deck?)

So yes, boats can have captains too.

A ship's captain will probably get annoyed if you call it a boat.

A boat's captain might merely correct you if you call it a ship.

See also:

• http://www.straightdope.com/columns/read/754/whats-the-difference-between-a-boat-and-a-ship
• http://mentalfloss.com/article/33557/what%E2%80%99s-difference-between-boat-and-ship