Easier said than done as you will always have to come to shore to restock and that is when those dasterly zombies will be waiting. Then if one of your crew is bitten and doesn't say anything, you will be hard pressed to escape on a boat, that is like a buffet for a zombie. Your only means for escape from a ship full of zombies would be to jump into the water to escape and then you have to worry about crocs or just being too tired to make it to the shore. And if you do make it to the shore you will be so tired, wet and cold that you will be easier prey for the zombies waiting for you.
I'm thinking, not written in stone, but to head out to The Rock, Alcatraz, fortify that place and stock it up so that nothing can leave or get on it without your knowledge. Somebody turns you lock them up and for fun torture the things until it expires. Or put it into one of those circus cannons and fire it across the bay. May even become a new game.