The concept of our ships are really advanced. Our sixth class, Pirate, will be able to experience sea life to it's maximum potential, but it will not be limited to that class. From start to maintenance to finish, the boats/ships will be executed to realistic detail. First off, you will have to purchase a ship building plan. There will be various sizes of boats/ships you can create, but that bigger ships will require bigger crews. Now you can either have a player/npc run company build your ship for a small fee, or can go about building it yourself. You must chop down trees, harvest lumber, purchase/create nails and tools, and actually build up the ship. Now the beauty of the sea life is that you'll be able to experience the life of a pirate to it's full potential. You'll be able to launch cannons, navigate courses/steer, connect + board other ships (battles). The point will be that there is going to be as much NPC filled 'ships' in the water as there are monsters on land. Jobs on the ship include the captain (navigation), cannoneer (loading/firing cannons), carpenter (restoring ships mid-sea damages), sailer (controls boat speed through sails), lookout (scopes/estimates time to land/ships nearby), and of course pirates (always ready for battle). There are so many underlying factors that will go into the production of the ship/boats (i.e. how damage to the ship will affect the crew on it, how boarding/attacking will work, how each job will function), but rest assured it will be in the beta version of the game.
To answer your question:
You must be a pirate to have a deed to a ship.
However, if you go up in ranks in a certain kingdom and achieve the rank of Admiral within the kingdom's rankings, you will be given the right to use a trade ship. Now, the ship won't have as much perks, but nonetheless, you can sail without being a pirate.
Also, things I didn't add in the description above is the sea to land battle. You can lay siege on an enemy town/city that has a port/is close to the water. In doing this, you can ransack the town/city for money/goods.