posted 10-16-2006 05:12 PM ET (US)            

Personally, the placement and location of various switches doesn't tell me much. What matters is where the wires go. But if you ask me, it shouldn't be all that hard to set it up so, if you need to, you can flip a switch or two, and combine the battery banks. I would have it so that, for each engine, there was a battery selector switch (1,2,OFF). From each switch, run a wire to each starting battery. Normally, you would just leave these set to their respective batteries (1 for engine one, 2 for engine 2). But if battery 1 dies, you can switch it over to battery 2 to start engine 1. Then, start engine 2. Then, switch engine 1 back to battery 1, so that you don't fry any alternators or batteries.

This would be independent of all other switching with regard to house banks, etc...

posted 10-17-2006 12:32 AM ET (US)            

As for how it ought to be wired, that is a matter of some preference. There are dozens of possible configurations. Exploring all of them is way beyond the scope of our discussion here. We focus on small boat systems, and a 31-foot with twin diesel inboards is at the very upper limit of that range.

posted 10-17-2006 01:11 AM ET (US)            

I have a 24 foot North Coast with twin Inboard Crusader 305's. Each has it's own independent electrical and charging system as does yours. My starboard side battery powers the bilge pumps and has a tendency to get too low to start the starboard engine if left for a couple weeks with significant rain. The way to utilize the fresh power of the port side without running jumpers is to have a parallel switch. It is a heavy duty button I press that connects the port side electrical to the starboard side and works like a charm for starting the starboard engine. Once the starboard engine fires up I let go of the switch and they are back to being completely separate systems again. This works great if the starboard battery is a little low. If the battery was dead I would run jumper cables and let it charge up a while before attempting to start. One other tip is to make sure the port (In this case) engine is running before engaging the parallel or engaging the jumper cables. (I always keep high quality jumper cables on the boat long enough to reach another boat)

As you state below you have a parallel switch. In my case I know my starboard battery is always going to be the dead one, so the parallel switch activates off of the port battery (Nothing runs off the port battery besides the port engine). The switch can't activate if you have it rigged from the dead battery. I believe there are more sophisticated systems you can purchase that can go both ways, but yours may be similar to mine. I recommend following the cables from your parallel switch down to your switch boxes and look at the layout. When the switch engages you should hear a fairly loud click. If you are not hearing the switch engage when both batteries have power then something is wrong with the rigging of the switch.

You might also try and determine why the batteries are always going dead. There must be a power drain somewhere that is causing the issue. If you are running electric accessories without the engines running you might want to consider shore power at your island, or firing up the engines when running more than just low voltage deck lights. If you aren't running any accessories and they are going dead, be sure to shutoff all the breakers at the panel, or completely shutoff the power at the perkos. You also might want to look at any systems that are hard wired to the batteries.

One sure way to have dead batteries is for a hard wired bilge pump to aerate, resulting in a continuously running pump. Or if you have old style float switches, they could get stuck and continuously run. Sometimes they are hard to hear. I have learned this lesson the hard way, so I make sure to inspect all bilge pumps before leaving the boat.

Good luck
Rolfe