Digital Switching

​Many benefits but a few downsides also​

By John Barry

Much has been written about digital switching on boats. The many features and capabilities of these systems are attractive to consumers who relish automation and artificial intelligence. There are also many benefits to boat builders that save time and money, including the need for less wire. Central control of systems including interior lighting and entertainment electronics is a great advantage of digital switching. But the technology presents disadvantages as well. Below we look at some of the problems and inherent shortcomings of digital switching.

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Digital switching opens up a wide variety of control and monitoring functions. A big risk is the single point of failure. Depending on the system, fail points in a digital switching system can be complex. Most systems use NMEA 2000, so if the backbone goes down so does control.

Single point of failure
A big risk of digital switching is the single point of failure. Manufacturers have addressed this with failsafe systems. A battery switch that stays on if it loses communication with the network is an example.

Depending on the system, fail points in a digital switching system can be complex. Most systems use NMEA 2000, so if the backbone goes down so does control. Systems have bypass capabilities for this situation. The procedure for bypassing digital switching varies by system. Take an example where the digital system controls the battery switches. In the event of a failure of a module, the battery switch could turn off unexpectedly and cause a dangerous situation. The remote battery switch has a bypass, but you have to go to the battery switch and turn the lever. This can be inconvenient at best. Module bypassing requires some knowledge.

Mark Roche of QCS Marine Electronics, Pensacola, FL, works extensively with digital switching systems. “There is no advantage to the troubleshooter with digital switching,” he says. “The advantages are in manufacturing and installation. It is essential to have manual bypass available for critical systems.”

A basic marine switching system includes a keypad, a DC interface, an AC interface and network cabling. Various modules are used throughout the network. It is important that the navigation network and the digital switching network are kept separate. If the digital switching goes out, the navigation equipment should continue to function.

As we know, digital switching uses a single power supply and draws power for modules that are responsible for the electronic switching. There may be a cabin lighting module located in a hanging locker and a pump module located in the bilge powered by a single supply. Since the modules are multifunctional and programmable, a failure of a single module could cause widespread failures.

Supply problems
The use of CANbus (NMEA 2000) isolates nodes to mitigate a problem caused by a failed module. There is also a chance for “block failure” of all interior lights caused by a single module or a more widespread failure of the pumps and lighting modules caused by a supply failure.

Once a failure occurs, the knowledge and process for manual bypass can be a critical safety issue. Training for operators should include how to deploy a flare, use a fire   extinguisher, call a Mayday and bypass the digital switching. There are many other aspects to consider, but the idea here is that you cannot call a Mayday if the power to your VHF radio is interrupted by a failure of the digital switching system.

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Setting up a digital switching system requires special software and training. Once configured, the files should be archived. Capturing and saving a file is essential for recovery from a crash. Knowledge about how to recover from a failure is important. Some systems are OEM only and very tightly controlled. This allows for increased reliability with centralized control of configuration files.

​Software issues
Digital switching uses NMEA 2000 to send PGN messages to the modules to turn things on and off. Based on CANbus, NMEA 2000 is robust and reliable when properly installed. The physical layer, connectors and cables remain a point of failure, but CANbus, in all of its iterations, is being used by many networks. NMEA 2000 is one version of CANbus. Other CAN networks, like J1939, have their place in the rapidly evolving marine network space.

Nevertheless, problems with the software side of the network can occur. If the network locks up, if a software update to one device takes another device offline, or if low voltage occurs on the network, central control may be lost and manual bypass is required. From main power loss to block failures or software issues, the fail states of digital switching are much different than finding a blown fuse in a traditionally wired boat. We see digital switching used in the midsized (20-100 feet) vessel market, but not on superyachts and  commercial sectors due to class requirements. This points to the fact that reliability of systems at sea translates to Safety of Life at Sea—SOLAS.Many systems are deployed on yachts that do not meet the basic concept that safety is first. It has often been said that, “Just because you can do something does not mean that you should do something.”  Wireless data links and gateways may be fun, but are they necessary? The KISS (Keep It Simple Stupid) theory should really be a rule!

​Serviceability
Keeping a digital switching system working reliably is primarily a function of proper installation. As systems age and connections deteriorate, modules and devices may get low voltage. When things get marginal, devices may fail and then troubleshooting ensues. A properly designed system has available manual bypasses for critical systems like bilge pumps, nav lights and electronics. But when failures occur and the boat returns to the dock, someone has to find and fix the problem. The challenges presented in troubleshooting digital switching can be daunting.

​I have spent a lot of time just trying to find a module. Where did they mount that thing? Documentation of these systems is essential. A configuration file should be saved if possible in order to recover from a corrupt software problem. Drawings should be detailed with locations, network addresses and settings noted. Using the installation notes in the NMEA 2000 protocol is a great idea here because a technician can view information from the network.

Digital switching systems are configured when they are installed, and documentation must be preserved. Changing or adding to a system is manufacturer specific, so trained individuals with proprietary software is usually required. Finding a blown fuse or failed breaker on an analog boat is a much different process than finding a failed module.

I heard a story of a boat that was underway at night when all systems failed. The motors continued to run, but no lights, no electronics. The operators lacked the knowledge to bypass the system. Those who advocate leaving the wet compass off the boat: this scenario ended successfully because the light from the cell phone let them navigate with the wet compass alone. Redundancy in the systems is the answer to this, a concept long embraced by the marine industry. It is the redundant power that is supplied by manual bypass that allows critical systems to remain functional.

Of course, digital switching manufacturers have different ways of accomplishing manual bypass. Some vessels are rigged for digital switching on most systems, but have traditional power supplied to bilge pumps, electronics and navigation lights. From moving a fuse to unplugging and replugging a connector, the methods for bypassing digital switching are many. When there are failures, someone on board needs to know how to accomplish the bypass. This means that the level of training must go up for the operator as well as the installer.

​Adding system loads
Digital switching uses a single supply line for multiple loads. So, if there are four cabins with lighting, a single line may supply an interior lighting module that supplies power to the lights. That same supply line may also provide power to a module for a stereo system and a module for fans. In this case, the single supply line must carry the load for all these systems, while each module has overcurrent protections for that module’s loads.

​Even after designing a system that is safe and properly fused, aftermarket rigging can introduce dangers. When additional loads are added to an existing system, there is a chance for overcurrent. As long as everything is fused, you are fine, but understanding what is fused and where it is fused may confuse aftermarket riggers and boat owners.

Hugh Lupo of New England Marine Electronics says, “I see a lot of violations of the ABYC (American Boat & Yacht Council) wire sizing standards in installations. The supply wires to the modules should be sized for the actual load.”

​An eye on obsolescence
Obsolescence is a problem. When a used boat is purchased, and there is no factory support or documentation of the vessel, failure usually means replacement. The configuration files and the drawings are of paramount importance for troubleshooting. If the physical layer is NMEA 2000, and still functional, a retrofit may be easier. Replacing a digital switching system is expensive and difficult. The lifespan of the wiring on a boat is limited, so retrofitting is in our future.

​Network engineers will solve many of these issues through innovative software solutions. Installers should keep it simple, as simple as the customer will allow. Educating the customer about manual bypass is essential.
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Redundancy is everywhere in the commercial world, and a good dose of redundancy on a yacht is an excellent idea. For instance, the emergency communications battery required by SOLAS and the USCG is to maintain safety. The backup battery runs the VHF, navigation lights, GPS and AIS. This requirement does not apply to pleasure boats that travel the same waters. Having redundant failsafe power supplies to these items seems logical to me.

Expertise required
Designing and installing a digital switching system requires a high level of expertise. Each manufacturer does things a little differently. Pitfalls abound from wire sizing and overcurrent protection to configuration issues. The overcurrent values are part of the configuration, and this represents a danger of misconfiguring and causing a fire hazard.
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There are rules and instructions to guide you to a safe installation when it comes to fire and reliability, but the configurations are also important to a successful system that maximizes safety and enjoyment. Designers must understand the rules and also the marine environment and the usage of the vessel in order to execute a good system.

NMEA teaches basic NMEA 2000 installation both online and in person. This class covers the physical layer of NMEA 2000 as well as introducing concepts of configuration and troubleshooting. The Advanced NMEA 2000 class is only taught in person and includes an in-depth look at the data and extensive hands-on training. Both classes are great for increasing your expertise in NMEA 2000. The network side of digital switching is straight-forward for an NMEA 2000 installer. The configuration requirements are manufacturer specific. The power distribution side is more difficult and requires ABYC knowledge.

Troubleshooting can be confusing. Since it is NMEA 2000, network problems may be detected and corrected traditionally, but when a failure occurs several systems may fail simultaneously. If there is documentation, finding a failed module may be straight-forward. Finding where in the boat the module is mounted may be challenging.
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Boats with digital switching that lack documentation should incur a service charge for “mapping” the system—that is creating a drawing by deduction. Once you have a basic understanding of what modules are on the network and where they are mounted, troubleshooting is easier. Understanding the distribution and configuration of the system allows logical troubleshooting to be performed.

​My take on the future
Any new systems that are introduced take time to refine. Digital switching is great for some systems and allows for easy monitoring, logging, etc.

As the industry evolves, I believe that common sense will prevail. Controlling the power supply digitally to a high amperage device like a windlass may be unnecessary. A network connection for controlling and monitoring the windlass is a benefit. This will eventually come down to defining which systems should and should not be part of a single point of failure.

Propulsion, steering and bilge pumps should have reliable and or redundant power supplies. Beyond this, I believe that other systems like the electronics (especially the VHF), navigation lights, AIS and GPS should not depend on a network for power supply. An aftermarket module that allows for rigging “other” items to the boat may be a good idea. Having a traditional redundant power supply to the helm for electronics is what this old guy likes. The evolution continues, stay tuned.
About the author

John Barry owns Technical Marine Support in Pleasant Prairie, WI. He has both FCC GMDSS Operator/Maintainer and GROL licenses and instructs all of NMEA’s technical courses. Barry is a former NMEA board member and current chair of the International Marine Electronics Alliance.