Even with 4/0 GA wire at 60' round trip the wire is dropping about 11.3% at 450A. This only gets compounded onto the voltage sag of the batteries. Most house banks will sag a couple of volts under a 450A load so your motor may really be seeing around 8V... Your best bet will be to always be running the engine and have a good sized alt, 150A+ to minimize the voltage sag on the system.. The voltage will still sag but hopefully the 100A or so the alt kicks in will keep the sag reasonable. A 24V bank is an option but it puts more weight in the bow and you will need a 12V to 24V battery to battery converter to charge the bow bank, if your current bank is 12V...