There are several techniques. I'd look into other modeling sites for how-tos. The model railroad community has a variety of products available to them to model water. Another good one is artist's acrylic gloss medium. That can be sculpted into waves and ripples.
One step up from blue cloth is a photo of the ocean surface. It's still 2-dimensional, but looks better than the cloth.
Please, your suggestions for learning how make or buy sea surfaces.
I've never attempted a water surface for a realistic sense of a vessel in water. At most I've done blue cloth! Please, can you recommend a source where I can learn to make [or acquire pre-made] sea surfaces?