question

Maybe a external Regulator with alternator temp control one for each alt as you have two motors (I would recommend a wakespeed WS500 reg) as the lithiums with place a very high load on those alternators and they may overheat, also suggest that you install serpentine drive belts, otherwise the normal v belts may need to be replaced oftern at these high load outputs

separating the alternator outputs is not required even if you use the presumed alternators current internal regulators.

However note at all times you should have a lead acid battery attached to the outputs incase there is a over voltage cell shutdown in the house bank batteries and thus the BMS causes a battery disconnect, (do not run a alternator open circuit, with no battery attached)

so you may need to install to Cyrix voltage sensitive relays or similar so that the Lead acid and lithium are isolated when there is a draw down on the house bank (no motors running)

or if you use the Orion TR smart charger DC to DC then you will need a few of these to get the full 115 amp output from each of the alternators.

There are lots of ways to implement this. so maybe do a wiring plan or seek qualified local advice.

Hi Paul,

the alternators are the standard 115AH ones and new as both engines are new. Alternators very well known as you can find them on every D1 20-60hp Volvo engine and they are capable of Max 60A continuous. I don‘t wanna squeeze Max out of the alternators, just make sure if I motor I don‘t destroy them or the lifepo4...and get some A in the house but they are my 3rd choice of charging source. 1x 30A Orion Takes 35A per alternator plus extra for some additional sources like ignition direct so all safe. New alternators don‘t make sense as the once I have are new and with an Orion all what need

I will implement as easy as possible reusing max what I have, means replacing lead house with raw cells+BMS+new main fuses and the lead shore power skylla charger to the Victron Phönix smart charger 50A. The 4xVictron MPPT 50/100 change settings. Between alternator and starter a Orion dc to dc each so Alternator are protected. Job done.
I have 2200W bifacial solar panels on the cat and they always deliver min 50A doesn‘t matter how cloudy it is or when sailing plus 60A from 2 engines and 50A from shore power charger run via portable genny I can charge with 160A if needed. And the 840AH bank lasts me 3 days without any charging....but solar array is massively overspeced so in 85% the house is full. It chargers the house from 20 to 80 SOC even on a very cloudy med day.