I poured very wet plaster over the base, then lifted the base an inch off the table and dropped it. That makes the plaster level and gets air bubbles out. You can clean up the plaster that glops (is that a word?) over the edge after it starts to set.
After that was dry, I dimpled the surface with a burr tool on my Dremel. This is very dusty!
Trace the outline of the hull. Using light spackling compound I formed the bow waves by hand.
Sprayed a coat of gray primer over everything, then a coat of the bluish ocean color, which I don't remember what it was exactly. Then airbrushed light blue or aqua near the hull outline and in streaks and spots along the wake.
Brushed a coat of Future over everything, but this started to fill in the dimples, so after it was dry I sprayed a coat of gloss lacquer.
Where the hull goes I smeared some spackling compound, and dripped some water on it so it was mushy, then pressed the hull down. Spackling mushed out around the hull and I smoothed it out into the wake. A wet Q-tip worked well for that.
Then touched up the waves with flat white dry brush.
This all worked better than I expected. The spackling looks very frothy.
Fred