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When you're talking about the design of the boat, you say "it".

When the boat is still being built, your say "it".

When the boat is nearing completion, you can say "it" or "she".

When the boat is floating in the water you probably say "she", unless there is still a lot of work to be done (e.g. no engine yet) then you say "it".

When the boat is officially launched and operating, you say "she". If you continue to say "it" at this point you are not incorrect but suspiciously untraditional. You are not playing the game.

If you are referring to a boat you don't really know anything about you may say "it" ("there's a big boat, it's coming this way"). But if you know its name, it's probably "she" ("there's the Waverley, she's on her way to Greenock").

If you are talking about boats in general, you say "it" ("when a boat is hit by a wave it heels over")

If you speak about a boat in complimentary terms, it's "she" ("she's a grand boat"). If you are being disparaging it may be it, but not necessarily ("it's as ugly as sin", "she's a grotty old tub").

If she has a boy's name, she's still she. "Boy James", "King Edward", "Sir David Attenborough"? The pronoun is she.

If it's a dumb barge (no engine), you say it. But if it's a rowing boat (no engine), you say she.