Whats the difference between a

If it can cross oceans and is above the surface it's a ship.

So a rowing boat that can cross oceans is ship?

A rowing boat is not intended to cross an ocean, nor can it carry people or cargo, survive a storm or carry sufficient supplies,or a radio, has no navigation lights etc.

You can cross a ocean in a truck inner tube if you're crazy and aren't worried about dying, but its not designed for it.

Only ships are designed for crossing oceans.

They would of been refered to in the language of the peoples using them, what they meant by what they called them is another matter.

They would of been refered to in the language of the peoples using them, what they meant by what they called them is another matter.