On top of the TV, there's a book titled, "After the Laki Eruptions: A History." It says that the ship's original crow's nest is now in the middle of town, and Magnus has written a note on it. After you read this, you'll see something different in the crow's nest.
Climb up and click on the little panel in the railing at the right to find a nifty little puzzle. Read to the end of this hint for a picture showing one way to do this.
The goal here is to make 11 groups of hexagons, 6 in each group, so that none of the groups touch. This isn't too hard, so you might want to just muck about and see what you can do on your own.
When you make a good group of six, it gets a blue outline around it and one of the lights at the right goes on. When all the lights are lit, you're done.
The pieces that are already in place when you start can't be moved; see the little nails in them?
You can make your groups of six in any design -- all clumped together or stretched out in a thin line. You can also connect two nailed pieces to make a single group of six, and sometimes you have to.