Actually, in that scale, acrylic gloss medium in several layers works very well. At 1/700, waves are miniscule unless you are in a hurricane. By lightly stippling the gloss medium you create excellent waves. If you want it to appear a little windier, bry brush with some light gray and off white for white caps - but do it sparingly and in one direction (otherwise it appears that the wind is swirling). Same with waves, set a direction and do all the waves in that way.