Wine WidgyTM is a 3½ inch diameter EVA foam disc that slips around the stem of any standard wine glass and secures the glass in place in a boat's cup holder. The disc is lightweight and floats without being waterlogged if it were to fall overboard. It is currently available in 4 colors, light red, blue, green and grey.
There are very few competetors for this particular product. When looking up wine drinking and boating, the only stemware holder shown is a 'Yoebi" which is a plastic insert which fits into a cupholder and you slide the base of the wine glass into a slot. The problem is several fold, it takes up the cupholder for anyone else to use, the wine glass is entirely above the deck surface making it more liable to be knocked into (or broken if glass) and it is more expensive.
Another competitor is a version of a plastic wine glass formed inside of an insulated tall cup. This still voids the idea of drinking out of a true wine glass as the outer glass is a regular insulated glass.