Raymarine Dragonfly

[Fomen]

Well, unfortunately when you run DC current over salt water (12 VDC from the battery), it immediately starts to corrode due to electrolysis. It's the same thing that happens when you blend ferrous and non-ferrous metals and submerge them in salt water. Some metals are more prone to electrolysis, thus they are intentionally used to divert corrosion away from the "important" components. If you've ever owned a boat with an outboard, you will see zinc anode plates affixed to the lower unit. By doing this, electrolysis occurs at the anode, and not on the outboard. So if salt water (even in minute amounts) gets into that card reader, and there is DC battery current pumping through it, it immediately starts to corrode. This could probably be overcome by smearing a really thin layer of clear silicone over the edges of the door to the SD Card. Not only will it help keep it closed, but it will waterproof it as well. If you do it, make sure you don't use 5200 or 6200 RTV silicone/adhesive, as you will probably never get the door back open. I haven't done it, but I think I will with whatever unit I buy.