In Boat Stereo and eventually towers?
 

Hi,

Running a 21ft classic Mastercraft with a custom tower. Currently no stereo in it and want to put something in:

What would be the minimum in-boat system that we should aim to get in with enough power to be pretty damn loud even over the sound of the engine like:

amp wattage,
amp ohms,
number of speakers,
speaker size,
wattage
Woofer wattage
Would we need an extra battery to power it?

Want to do this as cheap as possible and as we're in Ireland can't really get our hands easily on some Wetsounds or Exile so if we knew the wattages and stuff could source other speakers and amps from local stores. Much appreciated with any help. Got some advice on kicking up the wake on before on here and really happy with the suggestions we got:)