Poly varnish is very good stuff; the better water-based ones have nearly caught up with oil-based. (I used Target Coatings Pre-cat 8000 on my rudder, holding up very well under water!) You can mix in judicious doses of anti-skid powder if you like. But any film finish is titchy to repair and labor-intensive to completely re-do. And if water does get into wood sealed with a hardshell (film) finish, vapor pressure can kick off the varnish in chunks -- not a nice time.
For interior woodwork on boats, I'd use a quality crosslinked polyurethane or polycarbonate urethane. Finish all
surfaces when possible, even if they don't show, and pay extra care to exposed endgrain. Recoat when previous application is still 'green' or scuff-sand between coats to ensure good bonding.
If the wood has previous moisture damage, you can stabilize it with Smith's penetrating epoxy sealer. It is effective at plasticizing wood fibers, but about as noxious as anything you'll ever use. Then varnish as usual.
Here's a link for Target Coatings.
They make what I consider the finest low-VOC film finishes in the world. I haven't played with their EmTech 9300 polycarbonate yet, but I go thru appalling amounts of their 8000 Series PreCat. These products can be brushed, but HVLP spraying gives best results. BTW, these finishes can be ordered with or without amber tinting (overprint); the amber more closely mimics traditional alkyd varnish or shellac.