I have 6 prisms. They add a wonderful amount of light. This first photo
is under one prism in an otherwise dark quarter cabin
Ours lasted 26 years before leaks. They are bedded in a black something like Life Caulk. I've just started replacing them. The leaks were not around the bedding but rather in the silicon that glues the plastic prism into its aluminum
frame. The next two photos are an original prism and then a replacement.
notice the plastic prism is breaking down after 26 years in sun and salt
Here is a below deck view.
. It was hard to get detail in the strong light against the dark background. The inside finish is a plastic piece that may have been ordered from the same supplier.
Problem is these prisms were made by Bomar
. Pompenette, the dealer for Bomar
told me they haven't been made for years. Fortunately for me Ta-yang Shipbuilding the builders of Tayana boats knew exactly which parts
had been put in my boat and that had some new old stock that they shipped out the next day. I got enough to replace all 6 of mine. Two done four to go.
If I were looking to put in deck prisms and not limited by the existing holes in the deck I would choose prisms that are clamped to the deck by their metal frame not ones that are glued into their frame from above. I'm told this type of structural silicon is what holds plate glass onto skyscrapers but I'd prefer a bolted metal frame.
Overall I would recommend the use of deck prisms to increase light below. Measure carefully, cut, seal the deck core
carefully and you are good to go.