I'd like to share an exploit i found out while travelling from Menethil to Howling Fjord.So i was standing at the nose of the ship.
When i suddenly fell off but i didn't fall from the ship.Although i was in the water i was still moving
So I continued like this in howling fjord when i saw i was going towards a rock then with the ship i kinda got a little bit inside(sry for bad screenshot you can't see here that i'm inside the rock but still...)
Then i moved on the right of the ship and fell through the ground under northrend.You can also mount while standing in the water with the ship moving but unfortunately i haven't got screenshots for that.