When you are on the boat, you need to :
- Get the bucket on the deck.
- Get the rope on the deck. The bucket and the rope will form one single item.
- Get the mop on the deck.
- Select the roped bucket and throw it on the sea. You now have water for cleaning
- Wipe the floor with the mop, revealing the constellation that will give you the clues
- Use the telescope, and select the constellation, which is just to the right of the mast, and above the first golden line
- Now near the wheel, use the wooden panel
- The two lines are actually the same symbols mirrored. The first one is the swirly symbol. The second is the kind of key that points to the right. The thirdalso looks like a key to me, but pointing to the left. The last is like two flags with a line on top. When you've found the first line of symbols, just find their mirrored version on the second line.
A door will open and you will automaticaly proceed to the next area. Hope it's clear enough about the symbols