How do I increase water level

Raising the water level should be possible but will create a lot of lag (except when you use something like World-Edit). Instead, I suggest to use the clone command to clone your ship into an ocean, see: https://www.digminecraft.com/game_comma ... ommand.php for a short tutorial. You could also create a new world and use a tool like Mc-edit (http://www.mcedit.net) to copy and paste it into that new world.