How can I sneak on board without being seen

Hint 1 of 5:

You have to be practically invisible to do that.

Hint 2 of 5:

What is that ugly thing around the navigator head?

Hint 3 of 5:

It will make you invisible to ghosts.

Hint 4 of 5:

If you ask nicely, maybe the navigator head will let you use the necklace.