Rags brought his 21' Weldcraft with a 450 hp 8.1 liter with a Hamilton 212 pump.
This unit didn't come with a stereo of any kind....so we needed to put something in that will piss off the other fishermen out there.....as well as give him the drivin' music to be able to get up some of those gnarly rapids.

Here is what we installed:
Clarion M309 Marine CD/MP3 Player with USB/iPod inputs
Memphis Marine MR 5.750 5 Channel Amp (80x4, 350x1)
Memphis Power Reference 6.5" Coaxial Speakers up front x 4
Memphis Marine MM62 6.5" Coaxial Speakers in the rear
Digital Designs 12" 1000 series Woofer in a custom made ported enclosure

We were originally going to just put the Power Reference speakers in, but then I remember I had the Marine speakers for the golf cart project....so we used those.
So technically, power-wise, this boat is at:
50x4 up front, 80x2 in the rear and 350x1 for the subwoofer.

The fronts and rear sound perfect...and since it's an aluminum boat, projects the sound all around and does a good job of it.
The DD sub fit perfectly under the boat's front un-used cabin area, and the port loaded off the front live-well perfectly.....deep deeeeep bass inside and it carries VERY well outside...shaking things inside the garage while we were tuning it.

All in all, this boat system does exactly what Rags wanted it to do, all while only installing a very minimal footprint of electronics.