Simple electrical upgrade
Our 1973 Norlin 34 project boat had been used mainly for club racing in its latter years, and it showed. Among its many outdated systems was the battery-management setup. It was no worse than what I suspect can be found on many other boats of that vintage, but it would not suffice for extended cruising.
The two Group 27 90AH deep-cycle lead-acid batteries, one for house loads and one for starting, sat side-by-side under the nav-station seat. The charging cable from the 60-amp alternator went to a four-position battery switchOff/Battery 1/ Battery 2/Both. The battery capacity was inadequate to cope with the demands of night sailing or a weekend on the hook, and there was no way of telling the state of charge. The cables were a messancient, cracked, and corroded at the terminals, not to mention mostly the same colorblack, whether they were negative or positive. Basically, the electrical system was a disgrace, and I lived in fear of a fire.
Since both batteries had died last winter, I had every excuse to come up with a cost-effective solution that would bring Ostaras electrics into the modern world. This would involve enlarging the house bank; finding somewhere to put a dedicated starting battery; simplifying the switching; adding a battery combiner; replacing all the cables; adding a small solar panel to trickle-charge the house bank; and installing a battery monitor.
My first purchase was a pair of Group 27 90Ah deep-cycle flooded lead-acid batteries. This would almost double the house-bank capacity. Why flooded? Simple economics. They were half the cost of similarly sized absorbed glass mat (AGM) batteries and a third the cost of gel-cells. If I were living aboard, I might have reconsidered, but for weekend sailing and the odd week away, flooded batteries would do fine. With regular monitoring, good winter care, and an eagle eye on the electrolyte levels, you can get a good few years out of lead-acid batteries. The combined capacity of 180 AH would be marginal for many boats, but it was adequate for Ostaras modest electrical drawchartplotter, VHF, stereo. The nav lights, anchor light, and interior lights are all LEDs, which dramatically cut power consumption, and the Tacktick sailing instruments are solar-powered. There is no refrigerator.
I also bought a Group 24 starting battery, along with a battery box. I had to make room for the second house battery under the nav seat, which meant the starting battery had to be relocated.
The most common way of switching between two battery banks is the Off/1/2/Both four-position selector switch. Switch to 1, and the house bank draws from that battery, and only that battery is charged while the engine is running. In the 2 position, house loads are drawn from the #2 battery, which is also the only one charged. Both combines the batteries for charging and also for discharging. This is where you can come unstuck; you quite properly select Both for starting the engine and to charge both batteries when running under power, only to forget to switch over to your house battery when the engine is cut. Next morning, you realize youve drawn down both batteries to the point where theres not enough juice between them to start the engine.
Because we often sail with children and novices and wanted to eliminate any possibility of confusion, I decided to make the charging system idiotproofwell, foolproof at least. As the first step I bought a Blue Sea Systems Dual Circuit Plus battery switch. This switch isolates house and starting battery circuits. Switch to on, and current goes from start battery to start circuit only, and from house battery to house circuit only. You cannot mistakenly run down the start battery. If you need to combine both banks for starting, just switch to combine.