It's looking very good so far. Interesting to hear they had to stand and row!
I wouldn't add spray, actually, as it's hard to get the shapes right. Though it's nice to experiment of course. You'd need to add a low (~1m) v2. cloud layer and mask areas for the spray, perhaps slightly elongated patches the way Was describes, or from painted shader on the water plane. Very small scales for the cloud fractal, and quite some density. With low quality settings, the particles could look like water drops.
Another way would be to use that painted/ortho mask and an additional (warped) PF for variation of density to make a population of the internal rocks. Tiny sizes, very small spacing, glass shader if needed, though I'd say a default shader with reflection and translucency would work just as well on a bit of distance. I've done waterfalls like that.
Another way of doing all the splashes would be to make vector displacement maps (one with al splashes or more for each splash), which would displace the actual water plane into splashes. But that's quite some work too, and I've only managed to do that in Mudbox.
My Roman boat is still on the site, under 3D renders, a bit down. And thanks for the compliment