For a camera that can take some spray, the X-H1 should be fine. I havent been inpressed with what I've seen of Sony weather sealing.
The only ILCs that can take a proper heavy splash and most likely survive, as far as I know, are Olympus cameras, and perhaps the pro FF DSLRs (Nikon D5 style) with a choice lens. Maybe a Pentax model with the right lens.
For a great boat bag that has a rolltop (for splashes) and a submersible waterproof closure (for really wild stuff where you and/or the bag might fall into the water), I recommend a Watershed duffel bag with some photo inserts. The Goforth has a waist belt that is comfortable and allows for hands free walking but isn't quite stable enough for really aerobic stuff. The other models are just really good tough boat bags.
Alternatively, bags with a Tizip zipper are properly, sumbersibly waterproof as well. On a boat, where you are seated and can take splashes at any moment, I think the rolltop Watersheds offer more protection against surprise splashes just by letting the top hang down. When walking, the Tizip is quicker to open and close.
If you are confident your bag won't be submerged, a regular rolltop will work just fine as well.