Making Onboard Adjustments for a Mix of 12, 24 and 48 Volts

Voltage converters help cruisers meet the mix of ever-increasing onboard electronic needs.
48-volt marine inverter
The efficiency gained with a 48-volt marine inverter means less wasted power during the conversion process, less strain on the ­batteries, and longer operating times for electronics. Ed Sherman

For years, I’ve been touting the advantages of 24-volt DC systems on boats. Higher voltage equates to lower current and less electrical resistive loss in an onboard electrical system. Boatbuilders say that the primary reason they have not adopted 24 or higher voltages is a lack of available components. Well, rest assured, that is rapidly changing.

As with many marine systems, much of what we see on boats gets its start in much larger industry sectors, primarily automotive and recreational vehicles. In this case, the movement to all-electric or hybrid-electric propulsion systems in cars and light trucks is a primary driving force. Consumer demand for onboard equipment with functionality similar to a new Audi or Tesla plays a part as well. So, with that said, let’s look at where we are today, and at how to think about upgrades on an older boat or accessory choices on a new one. 

Electrical Fundamentals

One big worry about cruising boats and their wiring has to do with voltage drop, where battery-level voltage doesn’t actually reach the appliance the battery is supplying. Boats will often have longer wire runs than automotive applications. All wire has some inherent electrical resistance that will lower the voltage at the appliance. This is acceptable, to a point. 

The American Boat and Yacht Council and the International Standards Organization identify two levels of acceptable voltage drop for battery-powered direct current (DC) systems: 3 percent and 10 percent. The bigger the wire diameter, the less inherent resistance it will have. As for voltage, higher voltages mean that lower amperage is required to achieve the same level of power (watts). 

The math here is simple. Wattage (power) is equal to volts times amps. (I’m talking about DC applications here.) Things like power factor come into play with alternating current (AC) equipment. So, by using higher voltages, designers can generate higher power to run more electrically demanding DC equipment. And there is no question that modern cruising boats have considerably more gear on board than boats built 10 or 20 years ago.

Equipment Changes

Cruising boats have been working with 12 volts for decades. When I was cruising back in the late 1970s and ’80s, our boat was equipped with 12-volt battery power to run our VHF radio, loran-C, depth and speed gauges, an AM/FM stereo, and ­incandescent cabin and navigation lighting. 

We didn’t have shore power because we had no need for it. The alternator on the engine recharged the batteries. We read at night using oil lamps that essentially eliminated the need for electric cabin lights. We cooked with LPG. We used sun showers to heat our water, and our head was completely manual. We had manually operated and electric bilge pumps. Our wind instruments consisted of telltales in the rigging, a masthead indicator and a handheld velocity meter. Life was good and, by today’s standards, quite simple. Today, you’d be hard-pressed to buy a new boat without air conditioning, extensive refrigeration, a water heater, and an array of electronic equipment including radar, autopilot, television and LED lighting. 

Additionally, unlike my old cruiser with a fully mechanical diesel fuel-injection system, a modern cruiser is likely to have a fully electronic fuel-injection system, again requiring more electrical power. 

Oh, and let’s not forget the bow thruster, anchor windlass and electric winches for sailhandling. 

The bottom line is that electrical power demands on a new boat have continued to increase. Even though additions such as LED lighting draw a minuscule amount of current (amperes) compared with incandescent options, the sheer amount of equipment that modern boat buyers expect to have on board is considerable. 

48 Volts and New ­Technology

In the automotive and marine markets, there is still a vast amount of 12-volt electrical equipment in use and available. Interestingly, we seem to be jumping past the 24-volt options in many cases and going right into the 48-volt world. 

Generally speaking, 24-volt systems have been used for large diesel-engine starter motors and some high-current gear, such as bow thrusters and anchor windlasses, but have never caught on in a wholesale fashion, at least here in the US. Historically, some American builders embraced 32-volt systems, but those systems have largely been replaced as boats aged and equipment became nearly impossible to find. Today, you are likely to see a boat with a mix of 12-, 24- and 48-volt gear installed. 

The advantages to higher voltage include a significant weight savings in the wiring. Heavy-gauge wire cabling is just that: heavy. It’s also quite expensive. One cruising catamaran builder told me that by switching to a primarily 24-volt system, he was able to save approximately 1,000 pounds just in wire. 

Now that we are beginning to see lithium-battery technology taking over in the marine world, additional and rather significant weight savings are also coming into play. While 48-volt lithium-battery systems are now mainstream, 48-volt alternators are also becoming readily available. Lithium batteries weigh approximately one-third less than their lead-acid counterparts, and typically offer about 50 percent more usable energy. Companies such as Vetus, Kenyon, Victron and Mastervolt, as well as the RV and automotive sectors, are introducing 48-volt equipment at a noticeably increased rate. 

Even with this increase in equipment production, it’s still going to be a while ­before 12-volt gear is long forgotten. So, the question becomes how to mix and match voltages required on a new boat. 

Enter the DC-to-DC voltage converter. With these electronic marvels, we can step down voltages electronically from 48 to 12 or 24 volts, or step them up from 12 to 24 or 48 volts. Most modern cruising boats have at least one, and often several, of these converters. Expect to see more of these mixed systems as equipment manufacturers evolve and old inventory gets used up. 

Summing It All Up

I see no letup in the development of hybrid and fully electric power systems in the automotive world, and I believe that this reality will continue the drive toward higher DC voltage systems across the board. 

Marine industry standards ­development is currently underway to address things such as wire sizing and safe lithium-­battery installations, as well as electric propulsion for recreational boats. This fact is a true indicator that these changes to boats are imminent. Standards-writing bodies can’t afford to invest time without a clear signal of need from the industry. 

Consumer demand will continue to be a driver too, and I don’t see much interest in going back to sun showers and oil lamps on board.