What's the difference between a ship and a boat?

So I was watching a horror movie that takes place on a submarine (Below or something like that), and the crew of a submarine takes on some people who had been stranded in the ocean. One of the stranded people makes mention of being on the captain’s “ship” and the captain quickly corrects her that she is on a “boat”. I’ve also seen the reverse, where someone is on a destroyer or something, calls it a “boat” and is corrected and told they are on a “ship”.

My dad was in the Navy (on a submarine in fact) and I asked him, but he doesn’t remember the difference exactly since he hasn’t needed to know for about 30 years. So can my fellow Dopers help me out? What makes a boat and a ship different?

Ships carry boats. Except for submarines.

Not quite true.

The giant ore freighters of the Great Lakes are some of the largest water craft ever designed, & they are all called boats.

Ships are salt water craft.

Personally I believe a ship to be a large seagoing vessel while boat means a smaller vessel not used on the open sea.

Aren’t subs used in salt water and (for Ponster) on the open sea?

Maybe a better question would be how does the Navy differentiate between ships and boats?

From dictionary.com:


A vessel of considerable size for deep-water navigation.
A sailing vessel having three or more square-rigged masts.
An aircraft or spacecraft.


A relatively small, usually open craft of a size that might be carried aboard a **ship. ** :dubious:
An inland vessel of any size.
A ship or submarine. :dubious: :smack:

For submariners, ships are targets. Submarines are boats.

Hmm, re-reading the OP I realise that we’re talking about subs here.

With no knowledge whatsoever I’d say that what I and Ethilrist is correct as regards the English language but doesn’t refer to whatever the US navy (or any other) call their subs.

It seems Ethlirist may have got the answer on the first try, with submarines being an exception (possibly for the reason Elvis gave). I’ll have to see if this refreshes my dad’s memory.

I don’t understand Ethilrist’s exception. Ships carry boats - true. Submarines don’t carry boats, which makes them boats, not ships. The OP said that submariners regard their vessels as boats. No exception needed.

Submarines carry small boats for people to use to get to shore when a dock isn’t available.

Submarines are also not carried by ships except in James Bond movies, which is the other half of the exception.

You mean like an inflatable rubber raft? By that measure, even the smallest dinghy could be a ship. What happens if you remove all the lifeboats from the Pacific Princess? Does the ship then suddenly become a boat?

I understood the rule (more like a guideline, really) to mean that a ship is a water-going vessel large enough to carry other water-going vessels. Boats are small enough to be carried by other vessels.

The way I was told - growing up near a naval submarine base and then working for the commanding officer of that base - was that boats go under the water. Ships stay on top of the water. Except for “very small ‘ships’” such as PT boats.

The submarine is a variant of an earlier craft, the torpedo boat. The terminology carried over when these boats were made submersible.

The exception seemed to be in the dictionary’s definition, but it may have just been poor reading comprehension on my part.

Not exactly, although you have the correct period for the development of the nomenclature.

Submarines were always designed as submarines. Torpedo boats were always developed as small, fast, attack craft. They did share the use of the torpedo as their primary weapon, but they developed in very different ways. Torpedo boats were developed specifically to take advantage of Mr. Whitehead’s invention of the self-propelled torpedo. Submarines had been in (rather unsuccessful) development for over ninety years prior to that invention, taking full advantage of the Whitehead torpedo’s invention, but not being originally envisioned to use it.

However, the earliest submarines were called boats, simply because they were so small. (Size has always been a factor in determining which vessels will be called boats or ships–although the criteria changes with a certain frequency, following the normal development of language (meaning it is rarely supported by logic).) Even as late as WWII, there were only two or three submarines in the world that would have qualified for the term ship based upon their tonnage. By the time the U.S. began building boomers that were, indeed, much larger than destroyers (or even some cruisers), the term boat had been firmly attached to submarines and it is now a point of honor among submariners to decline to decribe their vessels as ships. (Remember, logic has little to do with choices in language.)

Regarding the OP, I have not yet ben able to find a current tonnage cut-off point for the U. S. Navy for ships and boats, but one can get a general idea by looking at their names. While all vessels are numbers, boats are only numbered while ships have names.

all vessels are numbers s/b “all vessels are numbered,” of course.

However, that does point out the Navy approach to the issue: until 1931, all submarines in the U. S. Navy were given only numbers, not names.

I can’t believe we got to message #19 and nobody remembered that the Master had spoken on this topic. (Unfortunately, his column is somewhat less comprehensive than what has already been said here, and he offered no greater authorities, either. Then he goes off on a completely unrelated subject. Not one of his better days.)

One point I’ve heard is that a vessel of any size is a “ship” to its skipper.

Not to a submarine captain. None would ever in a million years call his boat a “ship.” It’s a boat. No matter what the dictionary says.