When searching for the perfect cruising boat, the electrical systems rank fairly high in importance. Here are my thoughts on what to look for.
General. Most boats were wired properly when they were new. Ideally, the wiring was immaculate - every wire labeled, every connection well made, all the wires nicely routed and secured, and a nice notebook with the details of the schematics nicely laid out. Once the boat has been delivered and lived aboard for awhile, the new owner will undoubtedly want to add or change the wiring. Maybe add an HF radio, put a fan over the bed, perhaps add a USB charging jack in the cockpit, or add a watermaker. Then a few years later, the fan over the bed craps out, and since it wasn't all that effective anyway, the owner just removes it – but since he may want to replace it someday, he just disconnects the wire from the breaker panel and tapes the end, thinking he may reuse the wire someday. On a few wire runs, he didn't have a wire long enough, so he spliced it a few times along the way, and since he ran out of the blue wire he started with, he changed the color to brown at one of the splices. The original wire bundles were too full to add any more wires, so it was a lot easier to kind of drape it along the outside of the bundle, and rather than following the original bundle all the way, it required a lot less wire to take a shortcut here and there. Oh yeah, then there was the time he could only find un-tinned, single strand wire, so he used it 'temporarily' to add a new circuit ten years ago, until he got a chance to do it right. None of these changes were documented in any way – certainly not in that nice notebook that came with the boat.
You can expect that an older the boat will have a lot of wiring changes. Many owners are meticulous about their wiring, but just as many either don't know how to do the job correctly or are just sloppy. When searching for the right boat, take a look at the wiring, especially behind the electrical panel and in the engine room and see how the previous owner(s) did his wiring changes. Check for wires that are unmarked and/or which don't connect to anything, corroded terminals, loose connections, chafed insulation, and wires that aren't properly secured. See whether there is any documentation, and if so, whether it is up to date.
Every wire connected to the battery, positive bus bar or distribution panel should be protected either by a fuse or circuit breaker. The only exception is the cable connecting the starter battery to the starter. An unprotected wire is a fire hazard – if it develops a short by coming loose from a terminal or chafing through the insulation, the insulation will melt or catch fire and the wire will become red hot.
If AC circuits were added, check to see whether proper marine grade wiring was used … or was household Romex type cable used? Wires used for AC circuits on a boat should be stranded, have a minimum rating of 600 volts, a temperature rating of at least 140° F (60° C) , be fire retardant and moisture resistant. The cable rating should be marked on the wire. Wire types THW, TW, HWN, and AWM are some that are allowable.
Batteries. I've talked at length (ad nauseum?) about battery types in other blogs, so I won't repeat it here. A boat typically has two types of batteries, one for the starter and one to provide power to all the other electrical circuits on the boat. The starter battery is like an automotive battery – it cranks out a lot of amps for a few seconds, then is quickly recharged while the engine is running. Check it for corrosion on the terminals, loose connections, and make sure the wiring is secure and in good condition. A properly cared for starter battery will typically have a life of 5-7 years. Check the date on the battery to see whether it will need replacing soon. The starter battery is usually rated by its Cold Cranking Amps (CCA), which is the number of amps a battery can deliver for 30 seconds at 0°F while maintaining its voltage above 7.2 volts) and Marine Cranking Amps (MCA), similar but measured at 32°F instead of 0°F). The CCA and the MCA rating should be at least as high as the engine manufacturer specifications.
House batteries are usually deep discharge batteries and are rated in amp-hours (AH). To obtain an AH rating, the battery that is being tested has to be drained to the fully discharged state over the course of a specified amount of time. The amount of amperage that it supplied over the specified amount of time constitutes the AH rating. The faster a battery is drained, the less overall amperage is available. For example, if we discharge a battery over the course of 50 hours, the AH rating looks higher than if we discharge that same battery over the course of 1 hour. To make it simple to compare batteries, a standard time frame is used, and for deep cycle batteries that standard time frame is 20 hours. So, if a battery has a rating of 100AH @ 20 Hr rate, then that battery can power a load of 5 amps for 20 hours.
If the batteries are flooded, gel or AGM types, their usable lives will be much longer if they are never discharged below 50% of full charge. These batteries also charge much more slowly once they have been recharged to 80% of full charge, so unless the boat is on shore power, the batteries rarely get charged much beyond that. Thus, only about 25% of the battery's capacity is actually usable. On Nine of Cups, we have been happy with a 600 to 800 AH battery bank. Lithium ion batteries can be routinely discharged more deeply and can be recharged more quickly than traditional batteries, which means we could get by with a 300 to 400 AH battery bank. Marine deep discharge batteries typically range in capacity from 100 AH to 225 AH.
The battery arrangement I like is a starter battery and a separate house battery bank. Ideally, the starter battery should be totally isolated from the house batteries, kept fully charged, and only used for cranking the starter. It is a good idea to incorporate an emergency switch that can combine the batteries if necessary.
Good quality batteries, even if badly abused (like most batteries on cruising boats) will last at least three years. Wet cell and most AGM batteries, if treated well, frequently fully recharged and equalized on a regular basis, will last closer to seven years. Lithium ion batteries may last a full ten years. Since there is no way of knowing how the batteries were treated, it is best to assume any batteries more than 3-4 years old will need replacing.
DC to AC Inverters. Inverters are quite commonplace these days, ranging from small, inexpensive 50 watt units to units that provide several kilowatts. Here are some considerations:
Size. The size of the inverter required for a particular boat depends on the number and type of AC appliances that are expected to be used. It's an easy calculation – start with the wattage of the largest appliance you will be using, then add in the wattages of all other appliances you will be using at the same time. Compromises are usually necessary. We have a 2000 watt inverter aboard Cups, but it will only run about 1500 watts continuously. If we want to use the microwave, for example, since it uses 900 watts, we can only run one or two small appliances (like laptop chargers) simultaneously.
Battery and charging requirements. All those watts used to power your appliances are coming from the battery bank. Unless the battery bank is properly sized and can be recharged at a rate that keeps up with the power draw of the inverter, the batteries will quickly go dead. If we ran the microwave for 15 minutes, then a coffee maker for half an hour, we'd consume 60 AH of power, more than a third of our usable battery capacity if we had a 600 AH battery bank. At that rate, we'd be running the engine or generator several hours a day, even if we had solar and wind generators. The power required by many appliances is pretty startling, and we find we'd prefer doing without most of them rather than running the engine – unless, of course, we are on shore power.
Sine wave. Inverters come in two types: those that produce modified sine wave outputs and those that provide pure sine wave outputs. The modified sine wave inverters are less expensive and much more common. They work well for most loads, but may cause problems with some TVs, microwaves, laptops and printers. Pure sine wave inverters are more expensive, but work well with any AC device.
Chargers. Some inverters can be used in reverse. If connected to AC power, they can recharge the batteries. These are often high output, sophisticated 3-stage chargers, and can be used in lieu of a dedicated battery charger.
Lighting. LED lighting has pretty much replaced all the traditional lighting on boats, from interior reading lights to navigation lights – even spreader lights and spotlights. Many older boats still use incandescent lamps, but all can be updated - although it isn't always cheap. We've updated all the lights on Cups over the years and the power savings in a 12 volt world is significant. Some of the early versions didn't last long in the marine environment, but the quality seems to be improving. LEDs come in two or three wavelengths which produce a warmer or cooler light. We prefer the warmer lights below decks – they don't seem as harsh.
So … that's my take on boat electrical systems, and I'm sticking to it!