There are a number of things that can cause poor AM/FM reception in a marine environment. One of the most common causes is Antenna cable routing. When installing an AM/FM receiver on your vessel spend a little extra time to investigate the optimal routing of cables including any RCA cables. Ideally they should be run away from any other cable and or electric motors or potential sources of interference. Power cables are the worst source of interference and can be in bundles of cable so you may not realize they are there. AM reception requires a short Antenna cable run for optimum reception which is not that easily achieved on a lot of vessels especially when using mast style aerials.
Check that you have selected the correct Tuner Region in the settings menu as the default setting may be imcorrect for your location.