Susan - the boat trip will have a lot of singers/musicians on it. Some of them will be Mudcatters, others not. If Max was interested in going on a boat trip, it would possibly be the best one to combine music, song and sea. If he wanted to go fishing, quietly, one of the regular rod and line early morning boats would be a better bet.
As for fringe events. Many regular sessions or sings happen in pubs with limited space, or just not enough room for the number of people trying to get in. This you already know from past visits.
In some of them, its might be possible to ask the person who is running it to reserve enough space one session for some US Visitors, otherwise getting there early (before it kicks off) may work. Sometimes people move on elsewhere, and a space opens up if you are quick enough to get it before someone else spots it.
The advantage of a standalone Mudgather is that it can be organised at a time and location unlikely to be swamped by the regular fringe stuff. Of course, this year the Regatta and Folk Week clash, so in the early part of the week, the pubs are likely to be so full that there might not be room anywhere.

Les suggests spending some time with Whitby Scratch Morris. As he says, there are a few 'Catters in the scratch. I have found some Youtube clips of us, so you can be forewarned of what to expect.
Whitby Scratch - Handkies
Whitby Scratch - Sticks
Whitby Scratch - rapper
Somehow I seem to have avoided dancing in anything filmed, although I can be seen wandering randomly.
Quack!
Geoff.