Power Struggles
DC, AC and Boats

Ugh. The Electronics Draw Too Much Power.

Lots of people agree with this general premise, much less those who are close to the sea. At a recent conference, Google engineers said that the cost of power and air-conditioning to their computers was exceeeding the cost of the computers themselves. Large users of computers, like Google, are pressing their suppliers to make less demands for power and cooling, and, if it becomes an issue, to prefer efficiencies there over raw computer speed.

Beachwerks tracks development in energy-efficient computers, and can help you select the most appropriate new equipment, or make changes that improve the efficiency of what you have. Sometimes, that may be as simple as changing the way a piece of electronics is mounted, to improve airflow. Quite a number of computers and associated equipment have undocumented assumptions of their position and airflow requirements.

Take a power inventory based on the list below. In addition to the basic aspect of its need for 12 VDC, 120 VAC (or other odd voltages), how critical is the device's operation? Criticality can range from safety of life to entertainment grade.

Somewhat separate from criticality is the need for power conditioning or an Uninterruptible Power Supply (UPS).  You might have an entertainment device that won't tolerate variations, or it might make the singer...very...very...slow. 

Electrical Power Inventory for F/V ________________________
Component How critical? Power conditioning or UPS needed? 12 VDC current draw 120 VAC curret draw

Total Power Needs

As mentioned, there is a strong drive for energy-efficient computers. If you use a desktop/tower modular computer,  and it's a bit old, you may want it reevaluated.  Your total cost of ownership, which includes not just the computer but operating costs, may wind up being cheaper with a newer computer. The old computer may be quite useful ashore. It could also be used as an onboard "cold standby" unit, to be powered up, to support critical functions only, if the more energy-efficient main computer quits.

All sorts of boat electronics, especially things originally designed for use ashore, need to be examined for energy efficiency.  Keeping an old device, if its power draw forces you to upgrade generators or batteries, may be a false economy.

Inverter Needs

Many computers and associated equipment, such as video displays, can run natively on 12 volt DC. Some that don't advertise this only need a connector change to use DC; the existing AC power block just converts to 12 VDC.

In some cases, a more efficient inverter than you now have may be cost-effective; the prices are dropping.  When pricing inverters, be aware that some are much more expensive because they have in a built-in battery charger as well as the inverter. If you don't need battery charging, you will save a lot by not getting it. If you do need battery charging, explore the prices of having two inverters, one with the battery charging capacity you need, and one that simply converts DC to AC.

Most inverters produce AC output that may not be exactly like power on shore.  This might cause a buzz in a sound unit, or a clock  not keeping time. If you have such a problem, let's discuss it. Certain critical devices may need a higher-quality inverter, or it may be more cost-effective to get a DC version of the device and not worry about the inverter.

Related needs: Power Distribution and Grounding Systems

It can be awkward to run separate power cords, especially to sensors and isolated displays.  Some newer technologies can make that easier, as well as potentially replacing network  cable with wireless links. Proper grounding also is essential to proper electronic functioning. We make the caveat here that we are qualified to speak to the grounding requirements of electronics, but that overall boat grounding, like power generation, is the proper specialty of qualified marine electricians. We are computer and network engineers, not electrical power engineers, although the disciplines are closely related.

Dual-Use Cable

Two of the newer networking technologies, NMEA 2000 and Ethernet, have differing capabilities to deliver power over the cable used for data transmission. Universal Serial Bus (USB), which is used to connect peripheral devices to computers, also has a limited power distribution capability, which can be tricky to implement effectively.  

This brings us to a topic that may seem clerical and bothersome, but has enormous benefit in the long run:  a written inventory of your electronic equipment, which includes their power requirements.  Once that is available, it becomes practical to do a power budget. A power budget might show, for example, that you have USB devices that, if all were active at the same time, would pull 600 milliAmperes (mA), when USB normally can't supply more than 500 mA. You decide that all the devices might, under some circumstances, all be active, and you've been lucky. 

This is an area where our experience could help. We could point out that you could plug a second USB interface card into a modular computer, and that the pair of cards can give you a total of 1000 mA, 400 more than you need. The USB devices will work quite happily when connected to either controller. Our work would first consist of understanding the problem, or recognizing a potential problem. Once it was recognized, you'd need a $30 or so USB card, perhaps a few extra USB cables and hubs, and technician time to install the card and recable.

There are other techniques for making more power available through USB connectors. Some electronic devices only want power from USB, and don't actually connect to the computer.


Proper grounding is essential both for pure safety and for the reliable operation of electronics. Multiple standards need to be considered in electronic installations aboard boats, especially when equipment developed for homes and offices, rather than boats, are used.  The former assume compliance with the National Electrical Code, while for boats, there are the overlapping but partially distinct grounding standards of the National Marine Electronics Association (NMEA) and the American Boat & Yacht Council (ABYC).