Yes, the starting battery should be capable of starting the engine regardless of what is going on with the house bank, it it can't do that there's no point in it even being there.

Assuming the wiring looks good, it's possible the starting battery may be not in good shape, as a starting point I would want to charge it up fully and then have it load tested by a competent shop.

If it tests OK then I would start looking for bad connections and possibly an interconnect into the house bank that is bleeding power off the start battery. Saw a C36 with a similar battery setup that had a bad ground on the starter battery and caused this same issue.

In addition to what Bud suggested, you might want to look through the documentation you should have received with the boat for the 12V electrical distribution diagram. I had a look at the one available to members on the web site, which specifically states it is for hull #15 and it does not show a dedicated start battery, but it does show a separate engine battery switch that receives its power from the house battery switch. This would suggest that each hull probably has its own electrical distribution schematic. If that is the case and yours is missing I would suggest you contact Warren Pandy at Catalina and request a copy for your hull #48.

The other possibility, depending on whether these three batteries are in close proximity, is the possibility someone messed up the battery connections.

If you do have the wiring schematic for the 12 volt system, if you could post a copy it may help us troubleshoot the problem. Hope this helps.

Scott - According to what I know and that you mentioned - Since all 3 batteries are in parallel when they are all on, if the house battery is depleated and you place it in parallel with the starting battery - then the starting battery is working hard to charge the house battery and in addition it is trying to start the engine. It may not be able to handle the load. If the house battery is depleated I would turn off the house bank and separate it from the starting battery in order that the starting battery can start the engine. It is not advised to then turn on the house battery switch to charge them since the engine is already on. This may damage the alternator diodes. You may have to make it to shore and charge the house bank from shore power.

Scott, you have at least 2 issues to figure out. One is what the switch combinations do to deliver voltage to the starting circuit. The second is how your shore charger and alternator deliver charging current to your two battery banks.

In my case, for example, I have one switch (1, 2, both) with 1 being a large house bank and 2 being a group 27 starting battery. Both the shore charger and the alternator are wired to the switch so that they charge whatever the switch selection is. I do not use any fancy device to automatically charge the starting battery, but choose to manually set the switch to 2 or both occasionally.

My switch allows me to change the setting from 1 to 2 to both even with the engine running because it is a 'make before break' type. That means it physically completes the circuit for the new selection before opening the circuit on the existing connection. If your switch does not do that, you are temporarily opening the circuit and it can damage the diodes on your alternator if you switch while it is producing any significant current.

Scott, yes, it would be wise to figure out what it is you have by tracing wires and doing your own wiring diagram. These two discussions might help you decide what you eventually may want to do:

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: [url]http://c34.org/bbs/index.php/topic,6604.0.html[/url]

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
[url]http://forums.catalina.sailboatowners.com/showthread.php?t=137615[/url]

MaineSail really does a terrific job of explaining things. Thanks for re-posting the link, Stu.

Scott,
As Duane mentionned, you will have to trace the 12V wiring from the batteries to the switches and the starter. I own hull 15 and had to trace all the wiring as it did not quite match the information from Catalina. The wiring diagram is posted in the Member only section. I did not get a wiring diagram with the boat’s owner manual, I had to draw it out. The drawings in the manual are fairly generic. It also helps when you add more electrical gadgets. It is not too difficult but you will have to pull the switch panel off the bulkhead to trace properly. It is very congested behind that area. The drawings in the manual are fairly generic. It also helps when you add more electrical gadgets and you get to learn about your boat.

On our C375, the house batteries are tied to the battery selector switch. Whichever selected battery will feed the starter if the “Eng Bat” switch is on. The alternator only recharges the selected battery too. The battery charger does recharge both when hooked to shore power regardless of selector.

I am just wondering where the 27 battery is located. Not much room close enough to the switches. I would almost think this a previous owner add-on.
Can you post some pictures?

Andy, I am sure you don't keep your boat on the Lehigh River. :)

Former Lehigh Valley native; moved to FL in 2004.

That evil battery selector switch. Like discussing going aground, sailors are reluctant to talk about how many times this switch has gotten us into troubles when left in the "both" position....

But on our first boat the "both" position was not the source of our problem. It was using a less than a 100% full battery to start the engine by virtue of leaving the switch selected to the partially discharged house bank. Even though it may have started the engine, what was happening was the reduced arc was not cleaning the solenoid contacts. On our Universal 5432 diesel the solenoid contacts was a "disk" that rotated slightly after each start. Low energy starts left excessive carbon on the disk. When the disk rotates 360 degrees, you're trying to start the engine through carbon build-up that should not be there. Caused some anxious moments off Anacapa Island. Lesson learned: engines need high-energy starts. This does not mean you need a huge starting battery, rather you need a battery that delivers the amps without excessive voltage drop which means a battery that is at full capacity.

Anyway, we deep-sixed the evil switch. Alternator and sense to the house bank and an Echo Charger to charge the starting battery. Utilizing a voltage sensing relay is schematically the same. There should be an on/off switch in series between the house bank and main breaker panel, but all engine functions (panel, glow, fuel pump, start) were to the start battery through an isolated breaker. We could deeply deplete the house bank and not worry about engine starts. In an emergency we could cross-connect with jumper cables, but we never had to.

This will be a spring project for Whimsea here in CT. There's a storage area under the aft berth just port of the muffler. Planning a dedicated start AGM battery there and thus short battery cables to starter. Wire the engine panel, glow, and Echo to the +, toss the evil switch, have a beer.

Two other factors in 'high-energy' starts would be appropriately sized cables and clean, tight connections.