Welcome aboard…..from Central Florida.
You are on the right track horsepower-wise but the charging capability of the older engines is dismal at best.
Since the battery will probably be used for other duties as well as a cranking battery you may want to install a VSR between whatever "house" load the battery will supply and the battery.
A VSR is simply a voltage sensitive relay that will kick the battery off-line to the "house" at a voltage high enough to still allow the battery to start the engine. Blue Seas makes a good, cost effective one.
Secondly, the engine will only supply a couple amps at most at slower to mid-range cruise RPM and since you are doubling the required horsepower to the boat that is probably where the engine will see most of it’s service life……so be prepared.
Sounds like a nice project you have there and good luck with it.

Hello Mike and welcome to the club. I read your entire blog and enjoyed ever minute of it. I only wish I had the ability to do things like that. I am mechanical only! With what Pappy said am I to assume you are going to have a generator on board? I’m from TN and don’t know anything about these types of ships (in my book), but have you considered twin engines? I have always dreamed of twins just for the safety factor and maneuverability? Just my two cents and oh, us bass boaters wouldn’t go anywhere without at least a 1500 GPH bilge pump. Guess we forget our boat plugs more often than you guys do? LOL! Thanks for sharing your project with us.

Dan in TN

Boy, that boat is some nice! What nice work! It’s going to be a lot of fun!

I agree with everyone else that small outboard alternators leave something to be desired. For that matter, many bigger outboards do not have the alternator to power ship’s service loads, other than maybe running lights. I think that, if I were going to do what you’re going to do, I would get one of those little portable, stowable, 120 volt generators and then wire in a 20 amp battery charger, made for permanent marine installation, the type that bass boat guys use to charge their electric trolling motor batteries. You could have an engine battery and a ship’s service battery (or multiple SS batteries) with a VSR as Pappy suggests, but also have the ability to charge both banks with the 120 volt charger. You could also plug into shore power and charge them, when docked. Being in FL and GA, you’re going to want to run 12 volt fans in the pilot house, I bet; so you need power.

This is just my opinion; but there is some serious windage on that boat. If you could slip your mind into ’80s outboards, I’d suggest something from the 20/25/30/35 OMC engine family. They are very reliable work horses, salt water-capable and fairly simple to work on, compared to modern engines. Their displacement will allow you to turn into the wind with no problems and will breathe very easy at cruising speed. They often have electric start and battery charging, albeit minimal, adapt easily to remote controls and repair parts are plentiful.

Have fun!!