Going to be purchasing a new alternator for the boat and it will need to power a new stereo system (not ridiculous but good) as well as a flat screen and stereo system in the cabin. My friend who is going to be helping me said I should get a 200 amp version. What are your thoughts? I am not a stereo guy and really don't know what is needed or what is overkill?
thanks

Run it with the stock alternator and see how that works before upgrading to something you don't need.

What do you have now ? A 40 amp max motorola with a single v belt? 90 amp on a serp?
Clearance issues and chronic belt slip can accompany a big upgrade from the puny base alternators .
I have seen people add a second alt to those systems, opposite the power steering pump.
If your running a serp, should be able to bolt a beefy oem alt on there especially if you convert to the cast aluminum mounting system , a worthy upgrade in itself if your running steel accessory mounts

This is an older motor so it has a V belt and the old alternator is a prestolite 3 wire so probably not much. I also read that the higher amp ones might require 2 v-belts because of the slippage and come with 2 belt pulleys. It does have a large steel accessory mount.

I was looking at something like this but they also have a 160 amp.
https://www.dbelectrical.com/product...sal-mount.html

I would but this is a new build and I have the original alternator and do not want to install it. It is from 1990 and do not even want to chance it.

Make sure you confirm your wiring harness is up to the task (correct gauge) if increasing amperage output.

stock merc usually about 65amp, I have used the the 100 amp single wire ones and worked great, and yes good idea to upgrade the wire from alt to starter as well

The alt upgrade is worthwhile if your running audio amps and multiple batteries. You will definetly need a bigger power wire , if you have a 3point alt mount you may be able to wing it with one good belt if you can string it tight enough but 2 belts is much better.

The stock alternator wire, if I recall is 10 gauge, and, is not going to cut it when you upgrade alternators. I am running 100 AMP alternators on my engines, with 6 gauge wire from alternator to starter post. Single Vee belt on them, I have not had any belt slipping issues or anything like that. How big of a stereo system are we talking here?

http://www.genuinedealz.com/voltage-drop-calculator

Probably a couple of amps and a sub with a complete separate system for the cabin including a flat screen and video for the kids.

I have seen they have kits for these higher amp alternators
https://www.dbelectrical.com/product...y-0-gauge.html