Bob,

You are getting warm but, we do not know how many batteries you have. If you have a seperate starting battery, you would have a minimum of three batteries. The starting battery would be isolated from the main batteries. The standard set up is just two batteries, neither are starting batteries, they are just seperate house batteries. You would normally sellect #1 or #2 when at rest to reserve one bank for starting.

Many boats have been modified with the installation of additional house batteries, or have swithced to six volt golf cart batteries wired with two in series to supply 12 volts. Some have installed a seperate starting battery that is isolated from the house batteries and used only for starting.

There is no way for us to know how your boat is set up.

It does not sound as though your boat came with an owners manual, I do not know if Catalina can supply one for your boat. You could also try and find another C36 owner and see if he will let you copy his. It has a great deal of information in it regarding the basic boat and systems. It will include the basic wiring schematic, with that you can determine if you have the stock factory battery installation or not.

A few hours of reading this manual will give you a much greater understanding of your boat and systems and will add to your confidence.

Absent the Owner's Manual that Steve describes, you could do a search through your boat to identify all the batteries you have. The smallest one will at least be as large as a car battery. The largest could be one or more batteries, often much larger than a car battery, often paired (paralleled) as if they were one giant battery. (And some have replaced the large batteries, as Steve said, with an equivalent set of golf cart batteries.)

You then simply declare that the largest battery source is your "House Bank", the battery you would use most often. The other battery then becomes, by default, your stand-by starting battery. For this example, lets say your House Bank is #2, and the stand-by start battery is #1.

It used to be (and doubtless still is on many boats) that you would start the engine on #1, depart the marina, proceed underway, and after about 45 minutes (after the #1 has recharged following the starting load) you would switch to #2. Nowadays, the current thought (Ha! stupid pun!) is to ALWAYS use your House Bank, for start, departing, and for the full voyage, saving the stand-by battery exclusively for engine start in case you run the #2 flat. That's how we use it on my boat...never using the #1 stand-by start battery. The advantage of this method is that it simplifies life. My battery switch stays on #2 all the time. (But then, I have a charger, powered by shore power, that charges both #1 and #2 at the same time, when at the dock.)

The principle, as you have already guessed, is to never use the BOTH function, and ALWAYS keep the start battery isolated as your "get home" option in case you accidentally run the House Bank flat and are unable to get the engine started.

Steve and Larry are right: It All Depends on How It's Wired. In addition to your test, follow and physically trace the wires so you can draw a wiring diagram.

And the output of the alternator should be run to the house bank, NOT through the 1-2-B switch. You will need a way to charge the reserve bank, and that's where the 1-2-B switch can come in handy!

Bob, the fact that you need a little help with this issue suggests that you would really benefit by obtaining and reading:

Boatowner's Mechanical & Electrical Manual: How to Maintain, Repair, and Improve Your Boat's Essential Systems by Nigel Calder.

It is an incredible resource that I highly recommend. This is not directed just at Bob, but to all of us. Before we start tinkering with our boat's electrical systems and taking advice from other sailors (who may or many not know what they are talking about), we should arm ourselves with a good, sound understanding of how the systems work. This book does it.

Duane,
An excellent idea.
Bob,
If you are looking for an Owners Manual, there is one (actually two, both the MkI and MkII) in the Tech Notes CD. Plus a whole bunch of other stuff. It's available FREE with all three year memberships in C36IA. Just a thought.

Bob, since you seem to have 3 batteries, your boat wiring is obviously modified from the original and the manual might help you less than you hope.

I am going to assume you have 3 batteries, 2 under the starboard seat and 1 starting battery Gawd only knows where.

We have discussed these issues widely on the email newsgroups over the last few months. It sounds like your main batteries are wired in parallel for one bank and the starting battery is wired for another bank. This would not be my first choice, but it can work OK. Check to make sure battery position 2 is really both batteries in parallel by alternately disconnecting the positive cable from each battery in the compartment and seeing if the lamp lights with only one battery at a time in battery position 2. Obviously, I'd recommend connecting and disconnecting cables on with the selector switch turned off.

Go ahead and do the same test to the starting battery in #1 to verify your earlier assumption.

If this is all correct, then you should only have the battery selector switch on position #1 when starting the engine when the main batteries won't do the job. You should only have the switch to ALL while the engine is running. All other times the switch should be set to #2, the house main bank, or to OFF. If you normally are at a dock hooked up to shore power and your battery charger also charges the starting battery then you never should need to have the selector switch set to ALL while the engine is running.

Bob,

Again there could be equipment on your boat that you or we do not know about. One item is an echo charger, these are installed and charge seperate starting batteries off of the house bank when running the engine.

On my boat I make it a habit of always putting the battery select switch on both when running the engine to charge up all banks. As soon as I shut off the engine I select bank one or two so one bank is alway isolated.

Years ago I was crewing on an Islander 44, we sailed out to the Farlon Islands. While at anchor we sat and watched the Indy 500, In the morning we realized that we failed to isolate a battery bank. There was little or no wind and it required kedging off, rowing the anchor out a few hundred feet and pulling the boat out of the anchorage. It took about two hours to kedg our way out of the harbor and slowly ghost away from the island. I have since been pretty religous about isolating a battery. I also keep one of those sealed and charged jump start batteries on board.

Amen on the jump starter. I have gone out with people on night sails only to find the batteries on their boats won't start the engine. One had a jump starter and we were quickly on our way. The other did not and it was well after 3am when we finally got back on terra firma.

My boat has 4 golf cart batteries for house and a single dedicated starting battery. Extra weight to be sure, but also peace of mind. We can go 3 days before the house bank needs recharging, longer if in conservation mode but on a lake we are not really at any great risk of being stranded.

Bob, I'm glad you took my advice as it was intended. Some might have been offended, which was not my intention.

Now, as Steve so correctly keeps pointing out: you really don't know what ya' got until ya' know what ya' got. 12V systems can be very simple or very complex depending on what equipment is installed and exactly how it is connected.

For example: Your engine-driven alternator charging source could be wired to the 1/2/both switch and will charge whatever circuit or circuits the switch designates. Or, it could be wired to the house bank only and some device (like a battery combiner relay or diodes) charges the house bank from there, yet maintains the isolation.

Another thing is that most good 1/2/both switches will 'make-before-break' so that switching between 1/2/both is acceptable with the alternator producing output. Turning the switch to 'off' with the alternator producing current, however, will likely destroy the diodes in the alternator. This is because the current suddenly has no place to go (the batteries) and exceeds the limits of the diodes. To combat this, there are other devices which might be installed.

The point, again, is that you need to make a careful inventory of all the devices and how they are connected. You also need to understand (reference the book above) how the particular interconnections affect the operation.

Now, to answer your question: Yes, with the switch set to both, you would be drawing current from both sets of batteries (house and starting). I set the switch to only use the house bank (320 Amp-hours in 2 paralled 4Ds) for starting the engine and all house loads. The 'starting' battery is really an 'emergency' battery for me and I keep it isolated except when I specifically want to charge it.

The fact that I have 480 Watts of solar panels with two separate controllers gives me some options for charging that will differ from yours.

Good luck!

All of the above is correct as far as I can see. You may consider adding a battery isolator. I have a Hell Roaring Technologies BIC-95150B. Sounds odd, they're not in the normal marine catalogs, but make a line of these devices for RV, Boats and Trucks. It is a low draw device that's why I choose it.

The function is to bring the charging circuit into the isolator and let it distribute the current to each battery independently. That way each is charged whenever charging is occuring. I happen to have 3 charging sources, alternator, inverter/charger and solar pannels. All after appropriate voltage regulation come to the isolator, it distributes to each baattery. My unit favors the house bank and tops the auxillaries as needed. I stay on house all summer, save for one or two weekends when I operate off the aux bank to excerised them. I have 2 sets of AGM 31 series batteries in banks of 2 batteries (210 A-H per bank). At the end of the season I rotate the house and aux banks for the following season. The system works well, I'll attach the wiring diagram for my boat.

Lou Bruska
Sojourn C-36 MKI 1985 hull 495
Macatawa Bay (Holland, MI) Lake Michigan