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The electrical system: your boat’s lifeline

As today’s boats become more sophisticated, with more of our power-consuming shore-side comforts brought aboard, so do their power requirements. I’m not certain I want my boats to follow the path automobiles have taken, although I enjoy creature comforts.

The electrical system is relied on to power more technology than ever, even on small boats.

That’s not to say technology isn’t welcome aboard my boats — just that I truly want to understand what we are trying to achieve with it and be certain not to needlessly overcomplicate systems.

The DC electrical system on any boat is of primary importance for reliability and safety, but with today’s ramped-up electrical requirements we are putting it to the test. When I evaluated my 36-foot Albin trawler, I realized that during my 10-plus years of ownership I maintained the electrical system to very reasonable standards but did not consider that by taking advantage of current technology I could significantly enhance safety, simplify operation and make life aboard a lot better.
Here are some of the products that make life a bit easier.

The heart of any boat’s DC electrical system is its batteries. You can choose from conventional flooded cell batteries, head over to AGMs and gel cells, or push the envelope with the latest offering, lithium-ion batteries. Flooded cell (wet cell), gel and absorbed glass mat are versions of the lead acid battery.
The flooded cell battery is the least costly and is available in two styles: serviceable and maintenance-free. When I install flooded cell batteries I prefer the serviceable version, which allows me to check the specific gravity of the electrolyte and top it up when required. The gel cells and AGMs are considered specialty batteries and, although they have an initially higher cost, I find them a worthy investment.
Gel and AGM batteries aren’t prone to hydrogen gassing and pose no corrosion issues, unlike their flooded cell counterparts. They do, however, require a more specific charging regimen than conventional flooded cell batteries to extract all of their benefits.
Another benefit to gel and AGM technology is that their self-discharge rate is minimal, which is helpful if your boat remains unattended for long periods. My trawler is set up using serviceable flooded cell batteries for engine and house banks, and my twin-outboard center console works best with three AGMs.

Battery switches
Whatever your choice of batteries is, effective battery management is at the core of your electrical system. Battery switches are required by the American Boat and Yacht Council and exist so potentially destructive energy in the batteries can be isolated in the event of a fire. ABYC standard recommends: “A battery switch shall be mounted in a readily accessible location as close as practicable to the battery.” That can be difficult in all but the simplest of today’s boats.
While making them accessible and keeping them away from likely sources of fire (out of the machinery space) seems like a good idea, it often requires long, expensive cable runs, and the switch placement can be an eyesore. Thankfully, there are other options today. Remote battery switches, such as the ML-Series from Blue Sea Systems, can be used in place of many traditional manual battery switches. The ML battery switch can be mounted in close proximity to the battery bank, minimizing lengthy high-amperage cable runs and reducing the installation expense of long, heavy cables.
The ML switch can be remotely controlled through a traditional-style dash switch mounted at one or more of the helm stations and has provisions for a status-monitoring indicator LED. The switch also has a manual override knob providing battery circuit control directly at the switch, and it provides a “locked off” position for safe servicing at the batteries. If you’re running more than one battery bank and would like the option of paralleling banks for emergency engine starting, incorporating these switches simplifies the job and keeps it economical.
Although my trawler already has separate battery banks for starting and house loads, I plan to install a separate battery bank forward to power the bow thruster. That bank will eliminate running high-amperage cables through the entire length of the boat, and being able to install a remotely operated switch for this circuit greatly simplifies installation and operation.
There are still many installations that utilize traditional manual battery switches. Manual battery switches can be combined in almost any configuration to control different requirements aboard. With a bit of planning and a phone call to the manufacturer’s technical representative, seemingly complex issues often can be simplified. Aboard my twin-engine, outboard-powered center console, I use one battery for each engine and a third battery to power the electronics, including radar.
I wanted to be able to parallel any combination of batteries for emergency starting and have all three batteries being charged while under way. To accomplish that, I installed three of Blue Sea’s small M-Series four-position battery switches (one for each battery) and two automatic charging relays (one for each engine) for charge distribution. I now have complete flexibility in switching and charging.

Battery chargers have come a long way in terms of features, size and efficiency, the buzzword being “smart” charger. Smart chargers typically provide multistage charging that is often temperature-compensated, and some are capable of charging multiple banks at the same time. They offer selectable charge profiles for flooded cell, gel and AGM batteries, and have a much smaller footprint, allowing more convenient mounting options.
Additionally, many new chargers incorporate over-current, thermal and reverse-polarity protection. They run considerably quieter than older chargers and are well-shielded to prevent unwanted radio frequency interference and electromagnetic interference. You will also find waterproof chargers that are designed to be installed in smaller open boats, in addition to smart chargers that are portable.
Because of our desire to bring a little shore-side comfort and convenience on board, even trailer boats often have more than one battery or battery bank. Although many boats are single-engine, it is still important to be able to charge more than one battery bank while under way. It is certainly a requirement on larger boats that venture out for days or weeks at a time. Battery isolators have been used for this purpose, but they are not without issue. Isolators contain diodes that allow current flow into but not from the battery, but they also create a voltage drop that consumes charging current, creates heat and typically results in undercharged batteries.
Technology has provided us with a better way to charge multiple batteries from a single source: the automatic charging relay. These relays combine with electronic circuitry to accurately combine or disconnect batteries, based on the units’ preset parameters. The Blue Sea SI-Series ACR, which I have been using aboard my trawler, combines the engine starting bank with the house bank when the charging voltage reaches 13.5 volts, charging both sets of batteries simultaneously.
When the engine is shut down or the battery charger is turned off, the battery voltage drops rapidly. When it reaches 12.7 volts, 6 percent less than the “combine” voltage of 13.5 (13.5 – 6 percent = 12.7), and remains below that figure for a minute, the ACR opens to isolate the batteries. The ACR also incorporates a starter isolation circuit, which provides temporary isolation of the house loads from the engine cranking circuit. This feature can eliminate current surges that play havoc with electronics and appliances.
The most common method of charging batteries is the engine-driven alternator. Most OEM alternators are marinized automotive units that deliver only enough energy to charge the batteries and power a few on-board electrical devices. If we ask them to go beyond that, such as charging a good-size house bank while operating in the excessive heat of machinery spaces, we are exceeding their design limits, and their already marginal output can drop by 50 percent.
Today we have alternatives. Companies such as Balmar, Mastervolt and several others make good-quality, high-output alternators that can be installed in place of the factory units on your engine. Details of high-output alternators and their matched regulators are more involved than I can go into here, but be aware that when matched properly to a boat’s electrical system these external ”intelligent” voltage regulators can be used to precisely manage voltage, amperage and the multistep charging profile necessary to get the maximum life and performance from the batteries.
Although solar power has been more prevalent aboard sailboats, it is coming into its own aboard powerboats. Photovoltaic panels can be used to maintain a battery charge that is lost through self-discharge, and larger, more involved systems can be used to power appliances through inverters. Solar panels produce pure DC power, but most should be used with voltage regulation.
Single and multicrystalline panels are the traditional technology and have been around longest. They are the best for running large DC loads, such as lights, televisions and appliances. Amorphous thin-film silicon panels are only about 50 percent as efficient but are typically made in flexible forms that easily roll and conform to mounting surfaces.

There's more than meets the eye at the helm of the writer's 22-footer.

Voltmeters and monitors
There are numerous ways to monitor a boat’s DC electrical system. The simplest way is to install a digital voltmeter in the system. A high-quality voltmeter is important, as it is the only visual assurance that batteries and the charging system are at optimum levels. Although there are manufacturers of good analog meters, a high-quality digital voltmeter that will measure down to tenths of a volt is important. Many boats’ electrical panels incorporate analog meters, but I have found their accuracy to be questionable.
For the more discerning boater, digital multimeters are available, allowing one instrument to switch between displaying voltage and amperage (current) and also incorporating high- and low-voltage alarms. Voltmeter panels can be configured to monitor two or three battery banks by installing multiposition switches.
Going beyond the digital voltmeter is the battery monitor, such as the Battery Bug from Argus, the Xantrex LinkPro and LinkLITE, and the Blue Sea VSM 422. The Battery Bug displays battery and charging voltage, measures the batteries’ internal resistance and provides a digital picture of the battery’s age and capacity, displaying the charge level and percentage of remaining life. It provides alarm functions and can be installed with several battery configurations.
The Xantrex LinkLITE can be used for single- or two-battery banks. It indicates volts, amps, amp hours, state of charge and battery history, and has an alarm function. The LinkPro adds advanced and historical battery data and keeps track of more things than you can imagine. It is user-programmable for alerts and can be networked with other on-board electronics.
The Blue Sea VSM422 vessel system monitor is four meters in one and is less costly. It monitors the DC and AC electrical system, in addition to the levels of the bilge and a tank of your choosing (gray water, black water, potable water, fuel, etc.). By monitoring DC voltage, amperage and amp hours remaining, the VSM can provide timely information related to the batteries’ state of charge and help boaters avoid dead batteries at sea, according to Blue Sea. AC monitoring includes voltage, amperage, watts and frequency. Frequency is critical, especially when running an on-board generator.

The writer's Boston Whaler has three AGM batteries - one for each engine and one for the electronics.

Safety advances
There are several manufacturers that have incorporated LED power indicators into the boat-side plug of their shore-power cords. I have been using a 30-amp, power-indicating shore power cord from Furrion for the last two years year-round, and it remains like new. Although it’s not revolutionary, it is a nice addition. Marinco’s GalvanAlert is a 30-amp shore-power cord adapter that will indicate a reverse polarity condition with the shore power supply, eliminating the need to pull out a separate reverse polarity indicator each time you connect to shore power.
A major advance in the name of safety is the equipment leakage circuit interrupter. The ground fault circuit interrupter we are so familiar with is designed to protect against flaws in devices plugged into them, but it offers no protection from the danger of a failing hard-wired appliance, such as a water heater, cook top or air conditioner. The ELCI provides that additional protection.
The ELCI should be installed within 10 feet of the shore power inlet, and it provides ground fault protection for the entire AC shore power system. Although this device is typically factory-installed on new boats, retrofit components are available. In my opinion, it should be very high on the to-do list.
Galvanic isolators have been around for a long time, but it can be difficult to determine whether they are doing their job. They are designed to interrupt galvanic current flow with other boats and the dock. The ABYC eliminated the “Is it working?” concern with ABYC A-28, requiring the galvanic isolator to automatically self-test and be monitored. Monitoring is typically provided with remote panels and a series of LED indicators. Traditional unmonitored galvanic isolators and the ABYC-recommended monitored versions are available. Despite their higher initial cost, I strongly recommend the ABYC-compliant units.

The Blue Sea Si-Series automatic charging relay on Kehr's Albiin trawler combines the engine starting bank with the house bank when the charging voltage reaches 13.5 volts.

Inverters and gensets
Combination inverter/charger units use 12-volt DC energy from the battery bank and convert it to 120 volts AC, which can be used to operate standard household-type appliances, such as a small microwave, coffee maker, television and tools. They work well for variable demand loads of as much as 3,000 watts. If you have a need for additional power or want to run larger continuous loads, such as air conditioning, heating or refrigeration, a generator or a combination of both would be needed.
Aside from their rated output, the main difference between inverter types is their wave form. Modified sine wave inverters are the most popular, and they work well powering many common appliances. True sine wave inverters have a higher price tag but will operate all AC loads within an inverter’s specifications. It is the best choice for operating computers, stereos and other sensitive electronic devices that may not perform as well with a modified sine wave inverter.
Technology has made inverters smaller and much more efficient. Many are available with remote controls that allow programming and operation from the comfort of the cabin. There are sophisticated remotes that also serve as complete electrical system monitors. The battery chargers incorporated into these inverter/charger units function as well as and often better than standalone chargers.
Generators have seen similar technological improvements. Size, weight and noise have been reduced, and their overall efficiency has been increased, so it’s practical to equip almost any size boat with a generator. Xantrex’s Automatic Generator Start is a standalone product that automatically starts the genset when it senses low battery voltage, which can be caused by heavy inverter use or other DC loads. It also will automatically start the generator to run the air conditioning when a preset temperature is reached. The generator automatically shuts down after two hours of running unless it is switched over manually. The user also has the ability to program run and shutdown times, as well as quiet-time zones when the generator should not be run for environmental or other reasons.
The Dometic Group offers its SmartStart, which reduces the startup current spike of air conditioning compressors by as much as 65 percent, reducing strain on the generator. These spikes occur each time the compressor cycles on and they can make it difficult for some generators to handle the momentary load.
Another innovation for control of AC electricity is the Furrion Automatic Power Transfer Switch. The device is designed for automatic switching between shore power and the boat’s generator or inverter. It also provides a mechanical interlocking system to prevent two power sources from being connected simultaneously.
There many capable manufacturers of quality marine electrical components. I recommend visiting websites to browse the range of products and connect with technical advisers when you’re considering upgrades or replacement parts for your boat.


Argus Analyzers:

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BEP Marine:

Blue Sea Systems:

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Charles Industries:


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Magnum Energy:


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This article originally appeared in the April 2012 issue.