Solvents and chemicals are the worst things you can put on your screens. Furuno applies an anti-reflective coating to its products, and a surprising number of cleaners destroy it. Till says that some marine products are waterproof, but that doesn't mean they're built to withstand high-pressure hosing. Also CRT screens aren't nearly as waterproof as LCDs and extra care must be taken when cleaning these devices. Go with a mild misting with freshwater and, if serious washing is needed, put plastic covers in place beforehand. If freshwater doesn't do the trick, start with mild detergents such as boat soaps or hand soaps. Progress carefully to more aggressive products if necessary. "Our service department receives some seriously weathered screens for repair. After regular cleaning with freshwater, we often resort to a product from Chemtronics called Screen Prep," says Till. It's a two-part system that consists of a single-use wet wipe (deionized water and isopropanol), and a single-use dry wipe. Similar LCD cleaning kits can be purchased at most computer or home electronics stores. Navico has gone largely to glass screens, which better resist abrasion, but even they have coatings that can rub off. "No matter what kind of screen you have, you want to treat it much like a camera lens," says Bright. What about keeping screens clean at sea? Savvy captains keep a small spray bottle with freshwater nearby for rinsing.