Stereo equipment

I'm looking to replace my 6.5" speakers & my receiver in my boat and I'm unsure on what to look for, i know i need marine audio and that's about it. I'm looking for some input on what other people have purchased. I know they have this option in some vehicles and I'm not sure if it's something in the receiver or the other electronics but I'd like to get a receiver that the volume goes higher as the motor noise gets louder. Some of the brands i was looking at were Polk and Sony, maybe some JL or Clarion.

I don't know if you actually need Marine stuff if it isn't going to be getting direct water. If the deck is somewhere protected you probably can get just a regular car deck. What is your budget? You can get good value with the Polk DB series speakers. I have always liked pioneer decks. Do yourself a favor though and get an amp to run the speakers instead of using the deck to power them.