Whats the difference between a

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 was going to suggest without googling myself that the two may be different due to their primary use. So perhaps a boat is primarily for people to travel and a ship is for cargo, but not too sure to be honest. 

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.

To be a boat  is something small and a ship ️ is something big  but I’m not really an expert so what I say might be completely wrong 

So a rowing boat that can cross oceans is ship?

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

It can depend upon whether you are in conversation with the UK, the USA, or a submariner.

A fun to remember popular summary:

“You can put a boat on a ship, but you can’t put a ship on a boat.”

But what about this conundrum?:

“A ship has a commander and a crew. A boat just has whomever is on it at the time.”

Others will be hung-up on the myriad different hull profiles, summarising by the generality that:

"a V-shaped hull for deep water belongs to a ship. A flat-bottom, to a boat."

However, never mind all that, submariners refer to their vessel as a boat.

TheCatWoman said:

Ship and a boat, something I've never found a satisfactory answer too.

In theory all floating craft are boats but once you get big enough to be considered commercial then they get all snobby and call them ships.

Or if you are pompous and have a big, non commercial boat then you call it a yatcht and wear a skippers hat to hide your receding hairline... 

Just off the top of my head (no Googling) - Ship big, boat small?