I have a boat with a 24 volt starting system with 24 volt alternators. The rest of the boat is powered by 4- Group 31 12 volt batteries. I would like to use a inverter to charge the 12 volt house batteries when the 24 volt engines are running. Can you recommend an inverter or do you need to know the output of my alternators? Thanks, JS

It would be nice to have some clarification.
Semantics: Inverters- takes DC and makes AC
Converters- takes DC and makes another DC
Chargers- takes whatever (could be DC or could be AC) and charges battery.
End-goal is understood- charging 12V battery. But your technical path isn't so clear.
In order to make good implementation you need to know:

1. Alternator range of voltages? It is not exact 24V and in fact it is NOT 24v at all. And is this DC or you need to rectify AC?

2. Alternator ability for current (how many amps available from it)?

3. How fast would you like to charge your battery? Within 2 hours, 6....10....100 hours?

4. How big is your 12V battery bank?

Please try to find out as much as you can.