A cheap and easy solution that I use for rivers and lakes -- but that would work for seas as well -- is to take a big, clear plastic drop cloth of the sort professional painters often employ, and spray-paint the non-shiny side an appropriate blue. If you crumple the drop cloth up before spreading it out flat again for painting, you get pretty realistic wave effects.

Warlord Games do "Black Seas", "Victory at Sea" and "Cruel Seas" lines of naval wargames

Thanks, John. AFAIK, painters’ plastic drop sheets here are remarkably flimsy.
However, I’ll look into it as this sounds a good idea.

Donald

Donald
I have played cruel seas and victory at sea and enjoyed both. For an earlier period I can thoroughly recommend sails of glory. You will find gaming on anything but a flat surface will drive you nuts with ship models.waves may look good in the glossy photos but are not practical for moving,turning etc.