I hate quotes so i am not gonna use them.
1)Knives I can throw as many as I can 13 is not the max it's just an example.
2)If you are busy blocking my knives how are you gonna react fast enough to stab me 1st?
3)knife after knife as in I could throw a lot of knives at you while you try to kill me with a cutlass or reload.
4)and if you are engaged in a drunken brawl I am sure that'd make it even easier for me to kill you.
5)No, Ninja's can actually engage someone in the sea and land due the fact that humans are quite adaptable so sure Pirates can face a ninja off in land but I don't think Pirates are gonna win in land. So while a ninja can sneak abort your ship and ASSASSINATE YOU which as you said is something Ninjas can 'only' do. And what can a Pirate do anyways? Shoot a gun? swing his sword? Sail a ship? Drink till they faint?