Ever hear of pouring oil on troubled waters?
It actually DOES reduce wave action significantly. The problem is the quantity required to have a serious effect is enormous.
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Waves in the ocean are powered by wind. The wind first builds surface tension waves. It then pushes on the surface tension waves giving them energy, increasing their amplitude and wavelength until they become gravity waves. If you destroy the surface tension of water by coating it with a thin film of oil or soap you can reduce the surface tension waves and reduce the coupling between the winds and the waves creating a relatively smooth spot in the ocean, this is the origin of the phrase, "pouring oil on troubled waters."
Perhaps a few million gallons of oil might do it. Or a few billion gallons? Who knows?