Distributed Power Systems on an Average Cruising Boat: I say no!

Clark November 13th, 2014

Distributed power systems (or digital switching systems, or smart power systems, or intelligent, or multiplexing power systems…the industry is still settling on a name) are going into many new boats. I have a friend in the luxury power boat business, and he says distributed power systems save thousands of dollars, and reduce weight by hundreds of pounds, on every build. For builders it’s definitely the way to go for shipboard electrical systems. But is it right for owners?

If you’re not up on these systems, here’s what they do: Take the bow of your boat, where you might have some navigation lights, a windlass, a couple of reading lights in the forepeak, and a fan over the bunk. In a conventional installation you’d have a big set of cables running up to that windlass, a pair of wires to serve the nav lights, a pair to serve the fan, and a pair to serve the reading lights, but lights are often wired in parallel so that a pair of wires serves several cabin lights. In this conventional system, each circuit would have its own switch and its own fuse or breaker.

In a distributed power system a single pair of cables would run to a central location in the bow and terminate in a node or remote controlled breaker module (again, the industry hasn’t settled on one name). From this node, wires would branch out to the windlass, the nav lights, the fan, and the reading lights, but each device would be turned on and off through computer wizardry. You’d still have on-off switches for your reading lights, but the switches would actuate a breaker/switch within the bow node. All of these devices could also be controlled from a central location aboard.

The advantage of such a system is that instead of running four sets of wires to the bow, you only run one pair of cables and a tiny set of signal wires. Multiply this effect throughout a large boat with a complicated electrical system and it reduces the amount of wiring, and the time to install it, by a lot…by hundreds of pounds of wire, my friend says.

If you want to get fancy with one of these systems, the sky’s the limit. You could have a program, served from the central location, called “Night Sailing.” You press the night sailing button and the nav lights come on, the wind instruments, the electronics, and some very dim red footlights in the main cabin. You could have another program called “party time,” another called “night motoring” (add the steaming light), and one called “at anchor.” The system could tell you when a bulb blew out, or when something was consuming more power than normal, or when a bilge pump was running more than it should, or how cold it is in your freezer.

Manufacturers include Carling, with its Octoplex platform, Swedish company EmpirBus, and Capi2, just to name a few. Ben Ellison has written extensively on the subject on Panbo.

The problem with these systems, or the potential problem, is summed up in one word: Computer. There’s that saying about how to err is human, but to really screw things up it takes a computer, and I think I’d rather not have a computer controlling the juice to my shipboard electronics when I’m trying to thread the needle between a couple of ice bergs in shallow water to get into a tight anchorage before the storm blows in: “Oh yeah, no big deal, just have to re-boot the system and it’ll be fine. Oh wait, it seems to be hanging up. Let’s try de-powering it completely then re-install the configuration file…” You get the idea.

As I’ve said before, marine electricians and marine electronics experts (except those who make distributed electrical systems) seem more apt to quail at the mention of anything “networked,” be it the boat’s whole power system or just the electronics. We like things simple and field repairable.

Hallberg-Rassy uses the EmpirBus system on all of their new builds. The pages in the owner’s manual (section starts on page 20) that refer to the “state of the art distributed power system” scare me out of the whole idea: the recommended spares, troubleshooting, and contacting the EmpirBus dealer in say, Palau. With a conventional electrical system you could get away with a spares kit consisting of spare fuses/breaker, some wire, and some crimp-on lugs and connectors…and any marine electrician, anywhere in the world, could repair your system.

Manufacturers claim these systems are fairly dependable, but bugs, interoperability issues, and vendor reliability are always at play with any technology.

Still, the technology is probably too good to pass up on new builds for larger boats. Distributed power systems have been used on aircraft for decades and very few seem to fall out of the sky. Commercial aircraft have thousands of circuits, and some of these newer yachts may come close, but on an average cruising boat I draw the line. I’m saying there’s a sweet spot – somewhere – and below that it’s just not worth it.

I counted all the circuits on my 40-foot cruising boat, and I’ve got most of the gadgets. Forty circuits. All the lights, all the pumps, all the electronics, all the blowers and fans, and it adds up to forty different electricity-consuming devices. Forty circuits just doesn’t add up to enough complexity to warrant a distributed power system, in my book.

And here’s a second reason to ponder: LED lights. I’ve only changed a few of my shipboard lights to LEDs, but over time, as the old fixtures fail or get uglier, I’ll eventually switch all of my lights to LEDs. LED lights use less power, produce less heat, and thus use smaller wires. If one of the main goals of distributed power is to reduce wire weight, LED lights accomplish much of this same end when you consider that the majority of your onboard circuits service various lights. (Of the forty devices on my boat, half are lights.)

The current ABYC standard says that 16 gauge is the smallest wire you can use aboard a recreational yacht, unless it’s strictly a signal wire. Sixteen gauge is overkill for most LED lights. The pigtails coming off some new LED light fixtures are 20 gauge, maybe 22 (this is very small, like the size of a strand of dental floss). Point being, with wire this small, even at 18 or 16 gauge, you can serve all the lighting needs of an average cruising boat and the weight and complexity will be negligible. The wires feeding LED lights won’t be much bigger than the signal wires in a distributed power system. In other words, with or without distributed power systems, the wiring looms on the boats of the future will be much smaller anyway.

Don’t get me wrong, there’s definitely a place for distributed power systems in the marine world, and there’s no stopping progress, but I think it’s overkill and overcomplicating things for the average cruising boat. By average I mean a boat about like mine with something like forty circuits, and by cruising boat I mean likely to be in a place where parts and expertise may be months away.

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Comment by Richard
2015-02-09 08:45:39

I’m inclined to agree with you. A combination system is possibly a good way to go. Critical systems like engine start/stop, windlass control, radio, gps, bilge pumps should be wired conventionally as they are potentially life threatening if they fail or cannot be ‘fault found’ quickly. Things like nav lights, cabin lights, fans, electric winches etc could use distributed power as their failure, while quite serious is not comparable with the ones above. To not be able to start engine or drop anchor because of a computer glitch could be a nightmare scenario.

Comment by Clark Beek
2015-02-09 09:19:36

Hi Richard, Yes, that could work. I’m not sure if the starting circuit is part of a distributed power system in most cases. But yeah, bilge pumps, electronics, nav lights. Why make something complicated that’s so simple?

Comment by Adam
2016-03-02 09:08:39


Your explanation of distributed power isn’t particularly clear. The primary benefit is reduction in the distance and weight of cable run through the boat. Traditional “star system” electrical designs run heavy cables from the battery bank(s) to a breaker panel in a central area of the vessel. From there, every single branch circuit has to have a wire run from the panel back to the load. In many cases this means having cables doubled back over themselves, or running branch cables whose loads are located near other side by side for long distances.

This is terribly inefficient. It wastes space, causes packing of cables runs with the attendant issues (overheating, damage to conductors, and risk of insulation failure), adds weight and cost, makes adding new branch circuits difficult and expensive, requires running new cables when upsizing a circuit, exposes cables to excess electrical noise, and leads to the “cable to nowhere” syndrome in which anonymous wires are found peeking out of chases all over the boat, source and destination unknown.

Distributed power avoids all of these problems by running the heavy main bus from the battery bank(s) — typically in the lazarette — to the bow, and hanging “mini-panels” of a few breakers each in locations that are proximate to the loads they control. It is important to note that you **could** build a “distributed” power system using entirely traditional electrics, including bog-standard magnetic-hydraulic breakers. Doing so would address the negatives of centralized power systems cited above at the (major) cost of loss of the convenience and safety that comes with having all your power control in one location.

Modern distributed power systems address the convenience and safety issue by connecting a signal cable between all the breakers along the main power bus, and replacing the typical mechanical breakers with MOSFET switches that electronically control the current between the DC bus and the load. It is true that control of these electronics is “computerized” in the sense that there are digital signals that control their operation, but your evocation of a Windows NT-like blue screen scenario in the switching software is overblown. The antecedents of marine distributed power systems are industrial switching systems used to control stuff like factories, where the consequences of system failure are at least as large (and probably more expensive) than would be found on a cruising boat. Moreover, I am not aware of any system that does not also include direct manual control of the breakers themselves in the event that the control interface software has a problem (indeed, a failure or interruption in the control interface is materially more likely than in the circuit breaker firmware itself).

While I don’t disagree with you that in a cruising boat the benefits of simplicity and remote-repairability often trump those of fancy gadgets (though I say this as someone who ran from the U.S. to Australia on a 50′ Nordhavn with a full glass bridge and complex NMEA2000 sensor network, all of which I installed myself), I would argue that on both accounts distributed electronic power systems may in fact perform better than traditional centralized power schemes:

1. Shorter, easier-to-understand and more accessible cables runs mean the risk of hidden chafing and failure is drastically reduced, and make repairing problems far easier. You are never **not** going to know where your big 0000 bus cables are; with breakers located near the bus, the load runs will undoubtedly be shorter, more accessible, and more easily traced.

2. Because electronic circuit breakers are programmable, there is no need to carry replacement breakers of every rating. If I had a distributed power system I would at a minimum carry a full set of system components including a handful of breakers, but would not need 3 of every size from 1A to 50A. (That said, I would want to know from the manufacturer what data they had on situations that could result in the failure of multiple devices simultaneously or in a cascade, and plan accordingly.)

Clark, I absolutely agree that distributed power systems aren’t right for everyone. However, I don’t agree that they are necessarily wrong for cruising boats as a rule. The benefits, both to the builder and to owners, are very clear. Any new system architecture is going to require a change in thinking and an analysis and understanding of the risks as they relate to the benefits and to the new processes (both in manufacturing and operation) that pertain. But I think that an offhand dismissal ignores the upside of distributed power, which is, to my thinking, an objectively better approach to marine electrics. I’d argue that that the industry and cruisers alike would be better off if we encouraged more rapid adoption of distributed power technology and more competition among vendors to deliver efficient, accessible, and reliable products.

Formerly Nordhavn 47 “Eden”

Comment by Clark
2016-03-04 12:51:12

Hi Adam, I’m sure you’re right and it’s the way forward for many boats like your Nordhavn, but I’ll stick to my guns for a smaller, simpler cruising boat like mine. I think there’s a sweet spot, or a threshold. With 40-ish devices aboard it’s a fairly cheap and simple wiring job to have a “traditional” system. And I’ve read a few accounts of glitches with distributed power systems – one from Nigel Calder – where it took cracking open a system manual and figuring out how to reboot (this may not be the right term, as you point out). One you go above my hypothetical threshold, then distributed power systems are indisputably the right thing: cheaper, lighter, simpler. IE If I were buying my brand new 65-footer, and the broker was selling me on the state-of-the-art distributed power system, I’d say “terrific,” I’d get used to it, and probably love it.

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