PMDEVLIN - For low power the MP3 players are great, but for all but the faintest sounds you need an extra amplifier to get the sound level required. MP3 players are usually intended to drive headphones rather than loudspeakers. There are some out there who want the same sound level as with the full size, and that needs pure brute thrutch.
Wom - I was just referring to the '60's technology. Agreed the output transistors would benefit from being protected, but the capacitors shown would have the effect of smoothing off the high frequency edges presented to the speaker. The speaker used in a boat would probably be a single unit with plenty of mass, and so any signal presented above about 3.3K would be attenuated. In any case, the chip used to hold the sound sample would be one developed for voice recording, and so the output would stop there. Real HiFi demands a response up to over 20K, far beyond most human hearing, and these chips were probably developed with this market in mind. No values are given for either capacitors or inductors, but I suspect that they are small and aimed more at calming down the spurious responses to the amplifier's PWM switching when the speaker can respond to them. I reckon that with a single knobbly speaker, no-one would notice unless the speaker leads were long enough to radiate RF.
The big trouble is that the price was quoted in batches of 1000+.
In a boat, which is intrinsically a sealed box, any cooling will need forced flow, be it water or air. For air, a computer fan, should do the job. Even with a life of 4000 hours, thats 6 months running 24/7. At a couple of hours a week, its a long long time, and if its made accessible for replacement.....