An A4 or a small diesel are pretty easy to start. I’d guess the A4 needs 200 amps or less. My 36 HP Westerbeke needs 175. And a small Yanmar is around 165-180. Heck, I’ve seen lawn mowers with bigger engines than we have. And just about any motor cycle draws more cranking amps than one of our engines – yet uses a relatively tiny battery.
So just about any battery is sufficient for your starting needs. A honking group 31 diesel start battery with 900 AH or a 1000 amp 4D is a total waste of space and weight. As I’ve said before, the capacity of the battery is a function of the weight. More lead means more weight means more electrons to be used. And you can divide the weight up different ways for different uses. Lots of thin plates means lots of surface area to produce current, and thus lots of cranking amps. Typical design for an automotive start battery. But thin plates are susceptible to damage from vibration and shock. (The nice cushy suspension on your car keeps the battery comfortable, too. And think about the shock loading you get in the 4 foot chop in the Neuse.) Also, automotive batteries tend to self-discharge at a higher rate and may be more prone to sulfation during long term storage. And quick release of power is at the expense of reserve capacity. Fewer thick plates means less cranking power from the same weight of lead, but greater durability and much greater reserve capacity. In lieu of high bursts of cranking power, you get lower current flow for much longer periods of time. (Current flow x time (AH), BTW, is not a constant calculation. A battery that gives 5 hours at 20 amps draw (100AH) will produce a lot more than 100AH at 5 amps of current draw.) Thick plate are the norm in a deep cycle battery. The “marine start” batteries are a compromise between the two other types. Fewer plates and thicker for more durability, but less cranking power than an automotive type. Because “marine start” batteries are intended for boats, the cost may be higher than a deep cycle with a comparable weight of lead. Pick whatever is the best value. Personally I use a BC! 27 deep cycle for my starting battery, but that is mostly so all 5 batteries in the box are the same. I will probably replace the start battery with a BCI 24 whenever it needs to be replaced in order to save cost and weight (Imzadi has almost 1 degree of heel to port – mostly because there are about 400 pounds of batteries under the quarterberth.) And at the risk of opening a s**tstorm of comment, I use flooded Exide batteries purchased at Sam’s Club and WalMart. Cheap and durable – less than half the cost of comparable batteries from West Marine and a quarter the cost of an Optima AGM. Batteries on Imzadi date from 2011, and on Belle from 2003. And as far as the prospect of leaking acid when the boat is heeled – sailing at over 30 degrees of heel is both slow and uncomfortable, and if she is ever laid over on her beam ends I have bigger problems than a tablespoon or two of acid leaking into the battery boxes. YMMV, of course. Rick Brass Imzadi C&C 38 mk 2 la Belle Aurore C&C 25 mk1 Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of jtsails via CnC-List Sent: Monday, May 18, 2015 6:56 PM To: cnc-list@cnc-list.com Cc: jtsails Subject: Re: Stus-List House/starting batteries. I agree with everything Rick said, but I am going to throw a little different question into the equation. I was in the same boat (ha, ha) with bev last year. Over the winter I rebuilt the system with two group 31 flooded wet cells for the house bank and was hoping to repurpose the better grp24 from the old system as a dedicated start battery and an echo charger to keep it topped up. The old group 24 is too weak to start a cold Atomic 4 so it has to go....so the 64 dollar question is what do I replace it with, deep cycle (has plenty of amps to start an Atomic 4) or a car battery (lots of amps, will last a long time????) or maybe one of the in-betweens dual use batteries. I’m leaning toward the deep cycle or in-betweens. Thoughts? James C&C 38 “Delaney” Oriental, NC From: Rick Brass via CnC-List <mailto:cnc-list@cnc-list.com> Sent: Monday, May 18, 2015 6:19 PM To: cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> Cc: Rick Brass <mailto:rickbr...@earthlink.net> Subject: Re: Stus-List House/starting batteries. Bev; When I bought my first “real” boat (the C&C 25 that I still own) and was chartering in Chesapeake Bay in the early 90s, the practice you follow was the normal and preferred method of maintaining your batteries. On odd number days start with battery 1, switch to “all” for charging when the engine was running (assuming you had a “Make-before-break” battery switch so you would not blow out the diodes in the voltage regulator), and then switch back to battery 1 as the house bank when the engine was turned off. On even number days, same process using battery 2. But at the time, house loads were small. Refrigeration was a rarity. Ditto radar. No TVs. No microwaves. Just some lights and an FM radio. And boats had just two batteries – usually deep cycle 24s or 27s. As things changed and more “stuff” got installed on boats, the practice became having a large house bank and a smaller starting bank. For example, my 38 has 460AH of house and 95AH of starting battery, and the house bank will meet my needs for about 3 days at anchor. The norm changed to use the start battery just for starting the engine and the house bank for when the engine was off. Charge on “all” or just switch to the house bank for charging. That gives lots of AHs for running the “stuff” on the boat, and ensures you have a fully charged battery for starting the engine. The current best practice and preferred method has continued to evolve as more electronics and comfort gear continues to be a part of boating. Now the norm is more in line with what Edd Schilly just did in his rewiring. Big house bank. Small start battery. Start battery wired direct to starter for starting. Alternator wired directly to the house bank for charging, with an echo charger or ACR between house and start banks to recharge the start battery after the house bank is recharged. And you only use the 1-2-all switch (or a battery combiner) to combine the batteries if you need to start the engine using the house bank for some odd reason. The practice you follow still works just fine if you use your boat for day sailing or short trips, have 2 equal size batteries, and have the discipline to follow the process. My 25 has 2 group 27 deep cycle batteries and only a few lights and an electric head – and that is the process I still us. If you are a cruiser and spend more time on the hook with a boat having a significant amount of “comfort” gear, you should probably consider adding to the house bank and following one of the newer charging protocols. Rick Brass Imzadi C&C 38 mk 2 la Belle Aurore C&C 25 mk1 Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Bev Parslow via CnC-List Sent: Sunday, May 17, 2015 6:46 PM To: cnc-list@cnc-list.com Cc: Bev Parslow Subject: Stus-List House/starting batteries. House/starting batteries I have been in the habit of using battery one to start the 2gm diesel and then using the same battery for a house battery. Then the next day battery two to start the engine and then using that one as a house battery. This way each battery is being used to start the engine and also recharge the batteries. I have been told that this is incorrect. Am I correct or not? _____ _______________________________________________ Email address: CnC-List@cnc-list.com To change your list preferences, including unsubscribing -- go to the bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com
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