question on installing extra speakers.
 

first off this is for my boat not the car lol 4 is enough for that.

my boat is basically wired up like a car would be. it has a basic automotive cd head unit with 4 speakers. there are 2 inside the cabin and 2 out on deck. iv got a bunch of speakers sitting around from past cars and id like to install some more onto the boat. figure add another two on deck and 2 or 4 inside the cabin. is there a way to do this with out having to add any amps ?

If all you want is some sounds you can skip the amp and just splice. If you are worried about highest sound quality and perfect power level to drive said spaekers then you will need an amp or crossovers if you plan to use component sets.

2 speakers on one channel wired in parallel will drop impedance to 2 ohms and quite possibly put your radio into protection mode or worse ...