This video shows you how to install boat speakers from start to finish. The original cockpit speakers on my Beneteau 343 (2006 model) had broken grills and the plastic was starting to discolour cream. I took the grills off to see if they were separate to the speaker so I could order new ones only to find half the speakers were missing. To be fair the speakers were 17 years old and the marine environment is harsh. The speakers also provide a weatherproof seal if any waves or rain come in the cockpit, the speaker and cone prevents water tracking inside the boat. Old speakers could be the source of niggly leaks.
I decided to replace the speakers with 6.5 inch Sony XSMP1621 marine speakers. These speakers were just under £70 and provide excellent audio quality with great bass. Sony do another speaker that looks the same but its far cheaper using card instead of rubber around the speaker. The ones I installed have a much wider sound frequency range particularly the lower frequencies.
Before you start cutting holes in your boat, have a watch of the video as navigation equipment is susceptible to magnetic interference particularly from speakers.