More Power Scotty! Part Three

ScottyMorePowerAs with our other posts in this series, this one is going to get a bit technical, so if your heart doesn’t beat a little faster when contemplating voltage drop calculations, then you might want to skip this one. Just talk quietly among yourselves and be sure to check back in a week or two when I’m sure we’ll have something a bit lighter to reflect upon. Meanwhile, here’s a picture of the Big Sabine anchorage at Gulf Islands National Seashore taken on Memorial Day weekend.


OK, so, In More Power Scotty! Part One, we outlined our plan for transforming our DC electrical system from one designed for weekend cruising to one more suitable for a Life On The Hook™. In Part Two of the series, we selected our new batteries. In this installment, we roll up our sleeves and get to work.

As we previously mentioned, Eagle Too had a problem with her weight distribution. With a hundred feet of chain in the anchor locker, the dinghy on the foredeck, and a full water tank (located beneath the V-berth) she sat 2° low in the bow. It might not sound like a big deal, but the berth we sleep in runs athwartship (across the boat) and it felt like I was constantly rolling out of bed, which does not make for a good night’s sleep. It was a problem that was only going to get worse, because we plan on doubling our anchor size to 65 lbs and adding another 100 feet of chain to our rode before we embark on our five year (or longer) voyage of discovery. That would be over 400 more pounds of weight in the pointy end of the boat. I worried about plowing furrows through the ocean rather than rising gracefully to meet oncoming seas. To address the problem, we knew our 400 lbs of new batteries had to go aft. And the only place with the room was our cockpit lockers, or lazarettes as they’re known in the nautical world. They’d take up a lot of valuable storage space, but it was our best solution.

Flooded cells need to go into battery boxes. The job of the box is to catch any acid that might boil over during charging or spill when the boat is rocking and rolling. You don’t even want to contemplate doing without them, because having battery acid splash around places where it doesn’t belong can really make a mess of your gear, your boat and your day. But battery boxes aren’t sexy. Important, yes, but not something I wanted to spend a boat load of money on. And while there are some really nice (you might even say semi-sexy) boxes available, some of which even hold two six volt batteries each (because the boat runs on 12 volts after all, so you always use golf cart batteries in pairs), they were just too darned expensive. The boxes shouldn’t cost almost as much as the batteries they hold in my humble opinion. But after a bit of research, I found these online for only $7 apiece including tie down straps and brackets:


Here’s a closeup if you want the make and model:

Batteries33I found them at All Battery Sales and Service in Everett, Washington, who must not realize these can be used on boats, or they would have at least quadrupled the price. Six boxes including tie down straps delivered to Pensacola for less than $50? Sold!

With boxes in hand, we began working out our placement. Three fit nicely in the starboard lazarette without interfering with the access panel for the fuel tank:

Batteries30And the other three tucked into the port lazarette while still allowing access to the holding tank:


With the location for our new batteries established, we next had to determine how long our new battery cables needed to be to tie the batteries to our existing DC buss. After working out the best route through the boat’s inner recesses to run the cables, we used our handy fishtape to pull a length of 1/2″ line along the route. Once it was in place, we marked both ends with a Sharpie, and then pulled it back out (using it to pull a messenger line for later use). It was then just a matter of laying it out on the pier and measuring the distance between the two marks to determine exactly how long our new cables needed to be. We did this for both the positive supply and negative ground cable, as well as for the ones required to tie the individual batteries together into three 12 volt pairs.

The last thing we needed in order to place our cable order was to determine the required wire gauge, based on the maximum desired voltage drop from the battery charger to the new house bank. Fortunately, Blue Sea Systems makes a handy free phone app that does the calculations for you. Just enter the circuit length, amperage and desired voltage drop, and it tells you the appropriate wire size to use. You can find it here:

Blue Sea Systems Circuit Wizard

My research taught me that one of the major causes of premature battery failure is trying to go cheap with undersized cables from the battery charger to the bank. A 3% voltage drop may not sound like much, but it’s enough to make your charger think it’s done charging because it’s outputting 14.6 volts, while the batteries are actually only seeing about 14.1 volts and thus not coming up to a full charge when the charger quits for the day. Continually undercharging a battery results in uncharged plate material becoming permanently sulphated, resulting in lost capacity in a never ending cycle until the battery finally checks out. To make sure our new bank lasts as long as possible and always receives a full charge, we based our cables on maintaining less than a 1.5% voltage drop from the charger to the bank. The handy Circuit Wizard said this required us to use 4/0 cable for the bank supply and ground cables, and 1/0 for the battery interconnect cables.

With our wish list of new battery cables thus developed, I then visited to place our order. Actually, I shopped on their twin site I’m not sure what marketing purpose it serves, but both sites are run by the same company. The only difference is that the prices on Best Boat Wire are slightly lower, but you have to pay for shipping, while on Genuine Dealz you pay a slightly higher price, but shipping is included. If you’re in the market for new cables, it probably pays to shop both sites to see which one comes out cheaper. Since we were ordering about 80 pounds of cable, we saved a few dollars by going the free shipping route.

I was very happy with the service we received from these guys. They had a question about one of the cables I ordered, and called me for clarification. We received the entire order in about a week. One short jumper cable was made in black rather than red as I had requested, and when I called and pointed it out, they rushed me a replacement via 2nd Day postage. We requested heavy duty lugs and adhesive lined shrink tubing on all our cables, and I was quite impressed with how rugged everything looked.

Cables now in hand, we began pulling them though the route we’d traced using the messenger line we’d left in place…

BatteryCables1 BatteryCables2…and then hooked everything together to form the new house bank.


Starboard Lazarette


Port Lazarette

Fire is probably the worst of all possible things on a boat. Fires that can’t be put out in the first 15 or 20 seconds usually burn until the boat finally sinks. With over 600 amp hours of battery bank now onboard, I realized that if by some chance one of the main battery cables found a way to short itself out, we’d basically have the arc welder from hell, which would throw a fireball big enough to put a six foot hole in the boat. While there is a 50 amp DC main circuit breaker on the switch panel, and an additional battery breaker on the bank selector switch, neither of these were going to do a damn bit of good if the cable managed to short itself somewhere upstream of the main panel. For safety’s sake and following the ABYC guidelines, I installed main terminal fuses on each pair of batteries. A fuse for each pair was probably a bit of overkill—one fuse for the entire bank would suffice to prevent a fire if a battery cable shorted. But living as we do in one of the world’s lightning capitols, I have a deep and healthy respect for the mischief a close lightning strike can cause. Others have told tales about close strikes blowing up their batteries. I figured with a separate fuse for each pair, if we did suffer the misfortune of a close strike, maybe there’d be a chance that the fuses would save at least a couple of the batteries, allowing us to afterwards cobble together enough of an electrical system to start the engine.


You do have battery terminal fuses on your banks, yes? One nice thing is that the battery boxes were designed with the headroom to accommodate the height of the installed fuses.

These pictures were all taken during the final test fit by the way. I went back and added split ring lock washers to all the connections on the final tightening, and then sprayed them all with Boeshield T9, my favorite anti-corrosion spray. With an occasional wipe and a reapplication once or twice a year, these connections should remain bright and shiny for years.

So did the bank placement accomplish our goal of balancing the boat? After everything was in place, here’s the way Eagle Too now sits:

Batteries8Rather than being 2° down by the bow, she now sits 1° down by the stern. That seems just about right, as she should trim out perfectly when we add the additional chain and larger anchor to the bow. That’s an app called Clinometer by the way, which I find really useful. It’s available from iTunes and Google Play.

So that’s it for Part Three. In our next More Power Scotty! post, we’ll take a look at how we changed the whole charging system, and the new charging equipment we installed to maintain our new house bank and starting battery.

Care To Share Your Thoughts?