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 weren't called ships though.

Nor were coracles, reed boats, hollowed out logs or anything else.

A ship is substantial. Something like a minimum of 500-1,000 tonnes.

What about some Viking ship's/boats, not just the long ships, but knarrs that were longer range transport vessels?

I think carrying goods or people is part of the definition, I'd also suggest size, probably around 1,000 tonnes or greater (Cutty Sark is just under 1000 and is a ship), plus something to do with surviving storms and crossing oceans.

I'd disagree with you there, we have made boats that can be rowed across oceans, they do carry people, supplies etc and they can and do survive storms.

What would you describe the vessels of our pre-historic ancestors as? Some, maybe even most, hugged the coast and island hopped, but they did just launch themselves out into the water, in what must have been a massive leap of faith that they'd find land and they did, Australia was populated a long long time ago and the southern route to America is still being argued over. During the ice age sea levels would have been lower, but not so much that you could paddle to Australia or New Zealand or any other remote but long populated islands.

I've thought for a long time that ancient boat building was much more sophisticated than is thought and I'm always interested when ancient boat remains are found.

I'd disagree with you there, we have made boats that can be rowed across oceans, they do carry people, supplies etc and they can and do survive storms.

What would you describe the vessels of our pre-historic ancestors as? Some, maybe even most, hugged the coast and island hopped, but they did just launch themselves out into the water, in what must have been a massive leap of faith that they'd find land and they did, Australia was populated a long long time ago and the southern route to America is still being argued over. During the ice age sea levels would have been lower, but not so much that you could paddle to Australia or New Zealand or any other remote but long populated islands.

I've thought for a long time that ancient boat building was much more sophisticated than is thought and I'm always interested when ancient boat remains are found.