This is the simplest of all, using a solution that should have occurred to me several days ago. Oh well.
Use a distribution shader (with use Y and final position) to set up the waterline. The breakup shader is important here so you don't get an even line. This becomes the mask for the reflective shader and, inverted, is piped to the roughness function of the default shader where it is combined with the roughness map (multiplied, I think).
This is the sort of step that's better done in Terragen than earlier in the pipeline, because so much depends on the context and lighting. It's more subtle than the previous version (where the roughness was applied in Mixer) but better imho.
Done with this for now.
QuoteGreat improvement. Very convincing now. Perhaps a bit too 'fatty' water drips, but that's nitpicking.
Thanks, Ulco. About the fat drops, maybe? Some of the references I found show the oars shedding sheets of water, and the oar in the back is the animation frame where the sheet begins to break up into streams of drops. Anyway as I said this was mainly a test to see if it works. Blender's fluid simulation (like everything else with Blender these days) turned out to be much easier than I feared. Can't wait to play with it some more. Lots of possibilities.