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The Power Of A Lady

Three years ago, we bought a boat... shotly before we could afford it. I had been dreaming of the day for quite some time. I read PMM faithfully and spent countless hours poring over the articles and daydreaming in the classifieds. I had even completed the Power Squadron course.

My wife, Karin, however, didn't seem especially interested; occasionally she would bring me crashing back to reality with an offhand comment like "I get seasick." But still, in my dreams Karin would be enthusiastic. The money would be in the bank. The yacht club would be lying in wait. I would savour the months-even years-that we would spend looking for just the right boat.

And then it happened. I suggested we wander the brokerage dock on our way to the local watering hole for dinner one night. At the foot of the ramp lay Indigo Lady, an eight-meter Prowler, a flybridge cabin cruiser built by Cooper Yachts in British Columbia.

Karin liked the name. It was sunset on a warm spring evening and the place was quiet. I unzipped the cover over the aft deck and stuck my head inside. It smelled good...warm teak and canvas. The cabin door was open. Inside was beautiful teak cabinetry and rich, deep blue fabric upholstery.

The biggest obstacle to our boating future, Karin's lack of enthusiasm, slowly evaporated as she poked in cupboards and opened drawers. So enamoured was she that even her characteristic fear of debt abandoned her.

We owned our yacht two weeks later.

The Problem

Our first night at anchor was keenly anticipated. We had a bottle of our best Merlot, fresh focaccia, and prawns to accompany the fettuccini. Ella Fitzgerald sang in the background to set the mood, offset by Chloe and Duffy, our notyet- enthusiastic yacht Collies who were permanently underfoot.

All was right with the world until about late evening, when the lights began to dim and the fridge started to sound a bit feeble. By midnight it became evident that the boat's electrical system was one area we had not paid enough attention to when we purchased the boat.

We spent the next few weeks looking into what might be the best solution to the problem: staying within range of a marina with shorepower, so that the fridge would last the night.

What follows is a condensed version of all we learned in the quest for our ideal electrical system: one that could adequately provide for our comfort, be simple to install and operate, and not add too much to the burden of our slowly expanding nautical debt.

The end result is a system that provides enough power for a couple of days at anchor (three days if we're careful), a three-stage "smart" charging system, an inverter to provide power to AC receptacles, and a simple monitor. In its entirety, the system cost under $1,500, and we installed it ourselves.


It was clear the house batteries were old, or at the very least inadequate, so our first concern was replacing them. We quickly discovered that's a bit like trying to choose the "right" boat. The options are enormous.

A battery produces electrical current at a rate that is relative to the surface area of the plates inside it; more plates, more current.

The major factor affecting the robustness and longevity of a battery, however, is the thickness of these plates. Lots of thin plates generate higher amperage but don't make for a tough battery. Starting batteries are designed like this because lots of current is required.

House batteries, on the other hand, must be capable of many slow, deep discharge cycles and are therefore designed with fewer, thicker plates. They are referred to as deep cycle batteries and are the ones to choose for powering your house system. They also tend to be more expensive than starting batteries.

Having learned that, there is next the question of gel cell versus conventional, flooded batteries. Gel cells certainly have their advantages. They are maintenance free and will not leak or "gas," so never present the corrosion problems that flooded batteries can. Gel cells also tend to produce a more even voltage, in contrast to flooded batteries, which "drop off" more as they discharge.

Gel cells do, however, tend to be larger and heavier, their useful life expectancy is lower, and they are decidedly more expensive.

How Big?

Since we had no idea just how much power we used, we had to do a little research. The question we had to answer was "how big and how many?"

The standard unit of measure when comparing the capacity of marine deep cycle batteries is the amp hour (AH). A current draw of 10 amps for two hours would amount to 20 AH. The largest common size of a marine battery is the 8D battery, some of which can provide in excess of 200 AH but require at least two brothers-in-laws to move.

Which begs the question: Should we have several small batteries, or fewer big ones? My Scottish heritage required that I look for the lowest cost per AH while maintaining reasonable quality.

Indigo Lady is now equipped with a small TV and VCR; it is not uncommon for us to retire after dark to one of those old movies you can pick up by the dozen for $5 a week. And there's the little microwave that Mum and Dad bought us for Christmas. And we splurged on a bagel toaster.

These appliances all gobble power, so the first thing we had to do was estimate how much we used such devices in an average day. How fast electrical power is being fed to something is often measured in watts; watts are volts multiplied by amps.

A look at our appliance data plates revealed that most of the ones that operate on battery power of 12 volts direct current (12 VDC) are rated in amps, while the shore-powered ones that use 120 volts of alternating current (120 VAC) are rated in watts.

An inverter, if installed, converts the 12 VDC supplied by the batteries into 120 VAC for the AC receptacles on the boat. To estimate the 12 VDC current draw in amps of a 120 VAC appliance, one divides the watts by 10 (which allows a little extra for inverter inefficiency).

For example, a 1,000-watt microwave will draw about 100 amps out of a 12-volt battery. Run the microwave for six minutes, and 10 AH have been used.

We figured our daily requirements aboard Indigo Lady to be around 68 AH, if we really splurged (see table).

Unfortunately, choosing the appropriate battery capacity based on number is not exactly straightforward. For longest battery life, for example, batteries should not regularly be discharged below about 50 percent of their capacity.

And when recharging, the last 15 percent or so will go in quite slowly, so if we plan to be out for a while without shorepower, the useable capacity is really only about a third of the total amp hours rated for the batteries.

Since space in our engine room is rather limited, and we seldom have the time to go away for extended periods, we decided that batteries enough for two days between charging would suffice. Besides, we only have hot water if we run the engine, so charging the batteries is a good excuse for heating water.

What Kind?

Our initial inclination was to find the best buy on an 8D-size, deep cycle battery. The cost of these runs anywhere from around $150 for a basic flooded battery from a truck parts dealer, up to three times that amount for a high-quality marine gel cell.

Then we discovered golf cart batteries. Although they are 6-volt, they can be connected in pairs to produce 12 volts; they are good value, rugged, and of manageable size. Grandfather would be proud.

The difficulty of comparison shopping is that batteries for different applications are rated differently. The advertised capacity of marine deep cycle batteries is usually at a 20-hour discharge rate; in other words, the capacity of the battery when discharged at a rate that will kill them in 20 hours.

In the real world, golf cart batteries are discharged at a much higher rate; therefore, they are rated at the number of minutes they will last when discharged at 75 amps.

A battery will have a higher capacity if it is discharged slowly, so one that will deliver 7.5 amps for 20 hours (150 AH) will not deliver 75 amps for two hours (150 AH). Another thing to keep in mind when comparing capacity of sixand 12-volt batteries is that connecting 6-volt batteries in series will double the voltage but not the capacity, whereas connecting 12-volt batteries in parallel will double the capacity but not the voltage.

In the end, we bought two Exide E-2200 6- volt golf cart batteries, rated at 107 minutes, for under $70 each. I have since been able to establish that they have an honest 20-hour capacity of over 160 AH-a bit low, according to our calculations, but fine for our needs.

The batteries have a claimed life expectancy of over 500 cycles, if they are run dead at every discharge. If we multiply this by two (since we usually only discharge them to 50 percent), and if we assume 60 overnights per year (which we haven't quite managed yet), then they should do us about 20 years!

Charging System

Lately it seems that battery charging has become something of an art. A typical older generation charger delivers a constant voltage to the battery at some maximum amperage that varies almost in direct proportion to its purchase price.

There are two problems with using such a charger: The voltage is lower than ideal for much of the charging process, and it is too high once the battery is fully charged. Consequently, these chargers are a poor compromise. But thanks to the wonders of microprocessors, newer generation chargers have come to the rescue, breaking the charging process into three distinct stages, or phases.

The first is the bulk phase, during which current is supplied at the highest rate that both the charger and the battery will tolerate. Voltage during this phase is a result of the state of charge of the battery and climbs in relation to it. The charger monitors this voltage, and when it reaches a specific value-usually around 14.5 volts for flooded "wet" 12- volt batteries-the charger goes into the second phase, called the acceptance phase.

In the acceptance phase, voltage is held constant but amperage begins to drop off until the battery is fully charged-usually in about two hours.

The final stage is the float stage, which is designed to keep the battery at full charge without excessive "gassing." The float voltage is usually maintained around 13.5 volts. Three-phase charging ensures minimum charge time and maximum battery life.

Both the engine charging system and the shorepower charger that came with Indigo Lady were of the older constant voltage type, so we decided to treat our new batteries with respect and upgrade the charging system.

Although a three-stage charger would have been a perfect solution, we elected to go wholehog and install a combination three-phase charger with built-in inverter so we could also have 120 VAC power without an umbilical cord to the marina. You just never know when you'll need to charge the camcorder battery or fire up the blender!

The inverter/charger (I/C) we chose is a 1,000-watt unit made by Heart, and it has performed admirably. When shorepower is connected, it charges the batteries using the three-phase method. When shorepower is not available, the I/C can switch directions, if necessary, and convert battery power into 120 VAC. (On one recent occasion, I neglected to switch off the water heater before disconnecting shorepower. It was only the I/C cooling fan's barely audible hum that alerted me to the fact that our 1,000-watt inverter was dutifully delivering at least 1,500 watts to the water heater without complaint.)

One can expect to pay around $0.70 per watt of output from a good I/C.

The other charging source, the alternator, was the basic model that came with the boat's Merc 260 engine. Many alternators have a built-in voltage regulator that holds the alternator output at a constant voltage.

We wanted to take advantage of an aftermarket regulator that would make a three-phase charger out of the alternator as well. We found that Heart also makes one of those, which costs around $170. A trip to the local auto electrical repair shop was all it took to have our existing alternator tested and modified for connection to the new external regulator.

These steps have left us with an easily upgraded system. If the old alternator dies we can install a new, high-output unit that will work with our new regulator.


Once all this new stuff was installed, we needed to know just how well it would perform on Indigo Lady. After all, I wasn't going to spend all that money and have nothing to play with when I was done! (Karin calls me obsessivecompulsive, or anal-retentive, depending on her mood. There are drawbacks to being married to a psychologist).

In truth, the I/C and three-stage regulator look after flooded batteries very well without intervention. A periodic check of battery voltage or specific gravity will quickly determine stateof- charge. Having said that, however, it would still be nice to know how fast the batteries are charging or discharging, and when they should need recharging.

There are lots of monitors available that do this and more. Some are capable of tending to more than one bank of batteries at the same time, controlling the otherwise automatic function of the I/C. Had we chosen gel cell batteries, an I/C controller would have been an especially good idea, since these batteries are fussier about charging voltages.

But since our batteries are flooded, the standard settings of the I/C work fine. So we chose a reasonably basic model, also made by Heart, called the LINK 10. It cost around $200, and although it is not capable of controlling the I/C, it does display battery voltage, current flow in or out, total power used, and an estimate of the time remaining until the batteries are dead. It has just enough buttons to keep me happy but comes with built-in display "fuel gauge," which also keeps technically challenged crew members happy.


Installation concerns fell roughly into two categories: where to put things, and how to connect them. The Heart I/C is not certified for use around flammable fumes, and the unit does not like heat, so an engine room installation would not work.

In addition, the wire cables between the I/C and the batteries, which are located in the engine room, should be as short as possible. So deciding where to put the I/C proved to be a challenge.

In the end, we settled on a locker under the dinette seat, screwed the I/C to the aft bulkhead, and ran the cables aft under the head to the forward area of the engine compartment where the new batteries were located. The Heart brochure for the I/C said that it is "simply" installed in the incoming shorepower cable. Of course, in our case, that power cable ran down the other side of the boat.

We mounted the new batteries by placing them neatly in a row, building a low teak rail around them, screwing an anchor bolt into the floor at each end, and cinching them down with a nylon cargo strap. And we managed to do this without even puncturing the gas fuel tank underneath the area.

We mounted the three-stage regulator on a bulkhead close to the alternator, which eased connection.

A new hole was made in the electrical panel at the lower helm for the monitor. One of the nice things about the LINK 10 is that it is the size of a standard small-diameter instrument, so a two-inch hole saw made short work of the mounting process.


Connecting these devices together in the simplest, most effective configuration proved to be the biggest challenge of the project.

Each unit came with a manual and detailed wiring instructions, but, amazingly, none of Heart's product-specific instruction literature even mentioned the other units in the overall system. So it was left to us to integrate all of these products to each other, as well as integrate them into the boat's existing wiring...and all boats come with detailed wiring diagrams, right!?!

Suffice it to say I spent more than one evening at the kitchen table with paper and pencil and went through a number of erasers.

If deciding how to connect the wires was the most challenging mentally, then stringing them through the inside of the boat was the most challenging physically. On more than one occasion I was not sure I would be able to extricate myself from some space I had wedged myself into. I swear they built that boat around the wires.

But an obsessive-compulsive simply cannot sleep if any wires are not properly wire-tied, even if they run through areas never seen unless one crawls in bilge water with head wedged between the holding tank and the hot water heater.

We did end up at the auto electric shop several times for yet another roll of wire or longer battery cable, but it all went reasonably smoothly.

The DC System

The I/C instructions suggested two battery switches, one between the batteries and the DC loads and a second switch between the batteries and the I/C.

I felt that to be unnecessarily confusing and instead elected to connect the I/C through the main battery switch, as though it were simply another DC load. As there are no isolating diodes in our charging system, the position of this single battery switch also determines which batteries get charged. So we installed an 80-amp fuse immediately after the battery switch to guard against any major fault in the I/C or its DC cabling (see diagram).

The LINK monitor performs all of its magic simply by keeping a very accurate record of the current flowing into or out of the batteries at all times, and then doing the necessary math. It measures the current flow using a "shunt," which is a small, insulated block with two terminals and a calibrated resistance between them. The shunt must be installed between the system ground (the engine block) and the battery bank's negative terminal.

The monitor is then connected to the shunt through two sensor wires. In addition, the monitor requires its own power and ground as well as a voltage sensor wire direct to the battery's positive terminal.

The three-stage regulator came with good instructions, and after I had picked all I could from the brain of the kind fellow who modified our alternator, it was quite simple to install.

The AC System

Since the I/C will be damaged by connecting its output terminals to incoming shorepower, all AC on the boat must either be produced by the I/C or flow through it. By necessity, then, it is also a sophisticated switching device. When shorepower is available, AC current flows through the I/C to the AC receptacles while the charger element feeds the batteries as required.

When shorepower is disconnected, the I/C instantly comes online to produce AC power from the batteries. If no AC loads are present, the I/C just sits waiting and draws less than three AH per day. (If even that is too much, the inverter portion of the unit can be switched off completely.)

As a result, the AC connections on the I/C are relatively straightforward. Connect the shorepower supply to the AC IN terminals, and the boat's AC supply panel to the AC OUT terminals.


Once everything was installed and ready to go, we had a few adjustments to make. The three-stage regulator can be adjusted for both acceptance voltage and float voltage. Fortunately, it comes with a couple of indicator lights, so one can easily tell which stage it is in before making any adjustments. (We found that the factory settings were quite low and noticed a marked decrease in charging times when we turned them up.)

The monitor needs to know what the capacity of the battery bank is in order to accurately display the power remaining. Since we didn't really know what that true capacity was, we charged the batteries fully and then discharged them at a steady rate of about 10 amps. They lasted around 16 hours, and the monitor told us that 160 AH had flowed out of the bank.


Our new electrical system has gone through a couple of seasons now, and we're quite happy with it. There are a few things we pay particular attention to, a result of lessons learned the hard way.

As already mentioned, it is somewhat easy to forget to turn off large AC loads when disconnecting shorepower. If unnoticed, the automatic nature of the inverter means the water heater will drain the batteries in less than an hour.

When shorepower is not connected, we find only one large AC load can be used at a time. We can't, for instance, use the toaster or microwave unless the other AC loads are turned off.

Also, the battery switch must be set to "Both" to charge engine and house batteries simultaneously, either when the engine is running or when connected to shorepower.

When shorepower is connected and the battery switch is set to "Off," 12 VDC is still supplied to any DC house loads by the charger in the I/C. So if we want all power turned off for long-term storage, we have to make sure the batteries are turned off at the battery switch and shorepower is disconnected.

When at anchor, the battery switch must be set to the house battery bank only, or the starting batteries will be discharged as well.

The refrigeration unit is the major gobbler of our boat's power. We try not to open it any more often than necessary, as all the cold air spills out. We often turn it off before going to bed and rely on the Northwest climate and the insulation of the fridge to keep things cool overnight.

Finally, we've learned that the output of our old alternator is such that, unless we are particularly miserly with our power demands, the engine must be run for an hour and a half each day to charge the batteries.

A Moving Target

The electrical system and demands on the typical cruising powerboat are never static, and we are certainly no exception. A high-output alternator is already on the wish list.

Maybe also another pair of deep cycle batteries. And perhaps solar panels might be a good idea, even though they'll be somewhat limited by our Northwest weather...

Karin says I'm never happy; I say all progress begins with discontent. And I'm still looking forward to searching for the right next boat.

But finding it will ruin all the fun.