@Mat74UK In “as far as the eye can see” kind of way, absolutely yes. I live in Hawaii and have spent a good amount of time in coastal waters. On a nice day with very low wind and no swell, the ocean surface can be glassy. It is beautiful, it is incredible, it is quite an experience. The topography of the bottom of the ocean also plays a role. I was just in West Maui where there is a patch of ocean that is protected on many sides by the islands of Maui, Lanai, and Molokai. I spent several days boating in this area (which is actually a (federally?) protected sanctuary), and most of the days the water was glassy. This actually surprised me as I’m used to chop and winds on the west sides of islands during the winter.
Here is a photo of Waimea Bay on Oahu – it looks like this quite often during the summer unless there is a storm. And this is what it looks like on a winter day.