Find a spot in the water to put your pirate ship.
Make two small post in the water like this. Make the posts two high.
Build the hull of the boat.
Take the posts out from under the pirate ship.
Take the water out of the hull.
Build the deck of the boat.
Put the sails and torches on the boat.
Make a storage room in the hull of the boat.
This is how you make a pirate ship on Minecraft. Have fun and be creative. Here is a short video of the whole pirate ship.