More Power Scotty! Part One

ScottyMorePowerBefore we embark on our own five year mission to explore strange new worlds seeking out new life and new civilizations (OK, maybe new nightlife and new beach bars might be more appropriate) we need to channel our inner Scotty and make one giant leap in our ability to store power. The point of this blog is to share what we learn as we metamorphose from dirt-dwelling clock punchers to windborn gypsies living Life On The Hook™ (as well as keep my creative juices flowing while I work on the outline of the post-apocalyptic pirate novel I’d like to start writing. But it’s mostly about the sharing thing). So this is going to be the first in a series of posts that explains how we transformed Eagle Too’s electrical system from one suited primarily for weekend outings to one that can support the ability to boldly go where no couple has gone before on a 37 foot sailboat. Well, not too many couples. A few thousand maybe?

If this interests you, I think you’ll find some good stuff here. If this makes your eyes glaze over, don’t worry, just skip it. We’ll have some other stuff to talk about in between additional posts of More Power Scotty! Or there’s a great book I can recommend that I think you’ll enjoy. A week’s worth of entertainment for only $2.99. (or free through Kindle Unlimited) 🙂

So after months of deep thinking, weeks of sourcing parts looking for the best prices, and a major blow to the AMEX card, we finally had our new electrical system:

For starters, let me say that I think Hunter Marine actually did a pretty good job of designing the electrical system on the Hunter 376. It’s well suited for the way the majority of sailors use their boats, which is to sit at the dock on mild summer days drinking beer and entertaining friends, with the occasional day sail or night at anchor.

As you would expect, our boat has two battery banks—a house bank for the hotel loads (a single 4D battery) and a separate dedicated starting battery (single Group 24), maintained by a 30 amp Guest battery charger.


One of the best decisions they made was to use separate battery isolation switches for each bank rather than the dreaded A/Both/B switch that is so common on boats built to a price point.

BaterySwitchesWhat do I have against the ubiquitous A/Both/B battery switch? It forces you to be part of the charging system. You have to remember to switch it to Both if you want both banks charged while the engine is running or you’re plugged into shore power. You have to remember to switch it to A or B (usually A is the house bank) when you’re sailing or at anchor to isolate the starter battery. If you forget and leave it in Both, you could run all your batteries down and find yourself with too little juice left to start the engine after spending a lazy weekend out sailing.

You Won't Find One Of These On Eagle Too

You Won’t Find One Of These On Eagle Too

With all that battery switch turning, it’s inevitable that sooner or later someone is going to start the engine to get underway, remember they need to switch the position to Both so the engine’s alternator can charge both battery banks, and accidentally turn it to OFF by mistake, and POOF! like that, you’ve just fried the diodes in your alternator’s voltage regulator. A several hundred dollar (at least) mistake caused by inserting you into the charging system, a place where you really don’t belong.

The nice thing about having a simple On/Off switch for each bank is that you just don’t mess with them. Unless you’re going to be working on your electrical system or pulling one of the batteries, you just leave them in On. If you’re the ultra cautious type, you may turn them to Off when leaving the boat if nothing needs to remain energized in your absence, but let’s be honest here—how many of us actually shut off the batteries and close all the thru-hulls every time we jump in the dinghy to make a beer run? Regardless, there’s no switch turning occurring every time you start your engine or plug into shore power. Which greatly reduces the chance of you being a bonehead and frying your alternator.

So with each battery connected to its own battery isolation switch, how was battery charging handled? Hunter implemented a pretty simple and bonehead-proof system.

  • Most marine battery chargers have at least two, sometimes three separate DC outputs, which means they can charge multiple banks simultaneously. The 30 amp Guest battery charger on our boat had three ouputs, so Hunter wired one to the house bank, and another to the starting battery (and jumpered out the third output, but more on why that’s necessary in a later post), ensuring both banks were charged when plugged into shore power.
  • When underway with the engine running, they implemented a simple automatic bank paralleling system using a solenoid, or electrically controlled switch. Whenever the engine key is in the run position, a relay is energized that automatically completes a circuit that ties the two battery banks together. allowing both to be charged from the engine’s alternator. There are some other ways to accomplish this, but it doesn’t get much cheaper or simpler than a good ole’ low tech solenoid.
  • They installed a small deck-mounted solar panel to feed a steady trickle charge to the starting battery to make sure it’s always topped off.

So if the electrical system that came with the boat is so good, why do we want to change it? Because it’s just not set up for a Life On The Hook™. Here’s why:

  1. The house bank, a single 4D battery, is too small to keep the freezer and refrigerator running for more than a day. We know we need more batteries—a bank that can carry us through at least two, possibly three days before needing a charge.
  2. The current location of the house bank, under the port settee, didn’t leave room for more batteries. Nor did we want to add the additional weight that far forward. Eagle Too already sits about 2° down by the bow, and with our plans to add a bigger bow anchor and more chain in the future, we knew we needed to put the additional batteries well aft.
  3. While we ultimately plan to rely on 400 watts of solar panels to maintain the charge on our batteries, we intend to use a Honda portable generator for when the sun doesn’t shine (enough). The existing 30 amp battery charger is just too small for the house bank we feel we need, which would require a lot of run time on the generator to fully charge the bank. It also isn’t capable of doing an equalizing charge, which is very important to maintain the health of flooded lead acid batteries.
  4. A big negative of using a single battery charger on multiple banks or having an automatic bank paralleling system (or the use of an A/Both/B switch) is that since the house bank is much bigger than the starting battery and takes quite a while to charge, you end up drastically overcharging the starting battery in order to get the house bank close to full, significantly shortening its life. We’ve already noted battery acid in the bottom of the starting battery’s storage box that had boiled out due to overcharging. It’s a problem I knew would only get worse as we increased the size of the house bank.
  5. The spot on the deck where they mounted the small solar panel to keep the starting battery topped off while underway is a perfect spot to tie down gear when we load the boat up for cruising. Since the panel will end up being covered by something, it won’t work any longer.

So fixing those deficiencies defined our requirements. We wanted the following features in our new electrical system:

  • A much bigger house battery bank, located well aft
  • A bigger battery charger with an equalizing function, but not so big that it couldn’t be run from a Honda portable generator with some power left over to make hot water or run the microwave
  • All charging sources fed directly to the house bank, with a separate small serial charger to maintain the starting battery
  • A foolproof way to keep the starting battery isolated when not in use, and always at a full charge
  • Proper fusing for all batteries and charging sources
  • A way to monitor it all to keep an eye on the system’s daily operation

In More Power Scotty! Part Two, we’ll start to explain how we met these goals.

Care To Share Your Thoughts?