How can I get a plank?

Hint 1 of 4:

One pirate works with the plank. You heard that in the long discussion
between Long John Silver and another pirate in the ship's jail. And you have
an opportunity to see him working later.

Hint 2 of 4:

Speaking to him has no effect.

Hint 3 of 4:

Nothing can be done here.

Hint 4 of 4:

Try to MOVE(!!!) the man.