ith two staterooms, each with their own heads, a full galley and a comfortable salon, the fuel efficient single diesel engine Back Cove 41 may be the perfect long range cruising yacht. This innovative interior and deck plan will enhance your days on the water with comfortable seating and clear views of your surroundings.
boat unattended at a marina is that the shorepower could get disconnected, unplugged, the breaker may trip, or a variety of other mishaps could leave the boat unpowered and drain the house batteries. This is bad for the batteries and might result in other problems such as spoiled freezer food. We want the system to ride through a shorepower fault by failing over to the generator, running it if needed to save the batteries, and returning automatically to shorepower if the genset came back.
I’ll start with the equipment we installed and how the different components work together to solve the requirements we have itemized above.
The first step—and the most important part of the design—was to install a 240V, 60Hz inverter. This is the most important part of the design. Install a sufficiently large inverter system such that all appliances in the boat can be run off the inverter. On Dirona, we have a 4kW inverter to feed the 110V appliances, so 6kW is sufficient to support the 240V equipment we have on board. In our case, we installed two paralleled Victron 3kW, 110V inverters to achieve 6kW of 240V power. We particularly like this inverter choice because they are simple and don’t include a charger—all they can do is invert—and are capable of delivering far more than their specification. The inverters are specified to deliver 6kW at 240V, which is roughly 25A, but they can deliver peak loads over 50A and can operate for extended periods at or even beyond their rated output without sag, over-temperature, or cutting out. They are tanks, and just keep delivering no matter what. I’m amazed to report they can start the SCUBA compressor, where the required inrush current at startup can exceed 50A.
After a year of use, we continue to love these units. The key to making this design work is to ensure that the inverter capacity is sufficient to run the boat without restriction, using whatever combination of 240V equipment you need.
So, if you choose to duplicate this design, ensure you have adequate inverter capacity. 6kW is enough for us but you can get 240V inverters in a variety of sizes up to 20kW. And if your boat is 60Hz, you’ll need a 240V split-phase inverter—some appliances need that neutral connection.
The next logical step was to replace the ship’s service selector switch which, as delivered on Dirona, (leftmost of the three in the opening image) allows the operator to feed the 240V breaker panel from either shorepower or the generator. We replaced this new switch with one that adds support for a third input so we can feed the 240V panel and all 240V appliances on the boat from shorepower, generator, or inverter. This third position runs the entire house system off the new 240V inverter.
The third step is the switching. As delivered, the battery chargers on Dirona draw power from the 240V panel. In other words, one of the 240V “appliances” serves as the two battery chargers. It would be a very bad configuration to be running the 240V appliances off the inverter and have the battery chargers taking power from the inverter, using it to charge the batteries, which are then feeding the inverter. However, to support many of the use cases above, the chargers must be powered separately from the 240V panel. We want, for example, the 240V panel to be running off the inverter while the chargers are running off shorepower. So, we separated the battery chargers from the 240V panel and added a charger service switch to supply the chargers from either shorepower or the generator.
An electrical diagram showing these first three modifications is shown opposite.
The final component upgrade to complete the system was to replace the 85A start battery charger with a 190A at 24V alternator and installing heavier cabling for this larger alternator. The house battery bank already has a 190A at 24V alternator so, in this new configuration, we have two 190A at 24V alternators on the main engine. With the two alternators in aggregate, we have 9kW of power generation on the main engine. But, you probably wonder why we would ever want a 190A charger on the start battery system since the original 85A alternator was arguably already far more than would ever be required.
Well, it turns out that bigger is not really a problem in that a large alternator with a high quality smart regulator can produce whatever the start batteries need regardless of how low. So, having an extra-large alternator does no harm but is also