If you're interested in installing or replacing an on-board stereo system, don't just look for "marine" on the label. It doesn't necessarily mean the system can hold up to all of the effects of the typical cruising environment. Instead, make sure the manufacturer has specially treated the speakers and various internal components. For example, look for splashproof or even waterproof speakers; there's nothing like hosing down your deck and finding out the hard way you've ruined them. Also ensure the microprocessors and terminals are specially coated or plated, which helps them hold up to humidity.