This is assuming your taxpayer is not the owner of the boat.

There are a bunch of provisions for Fisherpersons, as long as you are describing a live-aboard, a share-of-the-catch, etc. If you have not done one before, I suggest passing on it or getting a mentor.

Because your taxpayer has a whole lot of stuff that has to be dealt with, and you are already stuck on some of the basics.

Oh, shoot. I just realized whose topic this is. That doesn't change my reply, though. It enhances that you are out of your depth on this entire subject for this taxpayer, of Fishing. Whether that also is true for the immense unpaid tax responsibility, there is not enough info to know if that is being addressed appropriately. It seems like everyone involved is either trying to avoid it or ignore it.