Can I Use the 24V House Battery Bank as a Backup for the 12V Engine Start Battery?

Question:

I am refitting a 46" sailboat, and considering a 24V house bank. My engine (Lehman 90) has two alternators (one with a double V belt). I was considering running a large output 24V alternator on the double groove for the house, and keeping the engine at 12V with its own alternator.  I would setup a 2000W inverter/charger on the 24V bank and keep a separate dedicated AC charger for the engine.

One of my concerns with this would be my reliance on the 12V system for starting without a good backup starting source (doubt I could get a DC/DC converter to run a starter that is practical for install in a 46’ sailboat) I guess I could use a jumper from 1/2 of the 24V house bank in an emergency?  Any thoughts? - John

Answer:

Great question, going with a 12 VDC engine start and then a 24 VDC house is pretty common. For back up of the engine 12 VDC, you could tap one half of your 24 VDC house bank. Depending on your engine 12 volt battery size, you could also carry a portable 12 volt car type booster.