How do I make sure the lighthouse stays off?

First of all, you need to keep the keepers distracted. If you've done that, make your way to the lighthouse itself.

The keeper won't be looking for his boot forever. There has to be a better way to make sure the lighthouse light doesn't come on.

It's 1650. To light a lighthouse, you light a fire.

To light a fire, you need to use firewood.

It's pretty hard to set wet wood on fire. Good thing it's raining so hard.

See that big firewood box in front of the lighthouse? The firewood will never get wet with that sturdy lid protecting it.

Let's get that box open, then. Tap for a closeup of the BOX LOCK.

That's an intricate lock for a box of firewood.

Not for you, though. You've solved much harder puzzles than this.

Tap the two outer rings to rotate. You will know the solution when you see it.

(SOLUTION FOLLOWS)

↓

Rotate the rings so that they align perfectly to form a TRIANGLE, a STAR and a HEXAGON.

Watch as the firewood gets drenched. No way it can be used for a fire today. (There aren't any other ships in the area, don't worry.)