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What's That Buzzing Sound? (Interference.)

Here’s a situation that might sound farfetched: A boater tells you that when their child watches a particular video on YouTube, the boat’s MOB alarm always goes off. Could these two things really be related? The answer is yes.

Electronics are proliferating on boats and more people than ever use cell phones and electronic tablets to navigate–and even to control their boat’s systems. As more devices on board use radio, it has become more important to plan how these radios will work together to avoid interference. This is a safety issue. Boaters may wish to reconsider controlling critical boat systems wirelessly when using frequencies that are subject to interference.

Luckily, the solution is not that difficult and is easily explained during a vessel exam. Make a list of every single “wireless” thing on board the boat that might be using a radio (including the radios). Look in each device’s specifications for its frequency: this should be a number labeled in Hz, MHz, or GHz. Devices with the same number or numbers that are close may interfere with each other. For example, the marina’s Wi-Fi (2.4GHz) can interfere with ZigBee MOB alarms (2.4GHz). Watching a high-resolution video generates a lot of Wi-Fi traffic, inadvertently sounding the MOB alarm because the MOB uses the same frequency.

You might notice radio interference as incorrect readings on wireless sensors; dropped sound (stuttering) or static in audio; pixelated or halting video; slow Internet speeds; speakers that click, hum, or buzz; or paired wireless devices that spontaneously unpair even though they are close together.

When buying electronics that include radio/wireless features, you can prevent this interference by avoiding frequencies that are already used on your boat. Let's walk through how a new equipment purchase could work with this in mind: Boaters with larger boats often buy hands-free wireless “intercom” headsets to facilitate communication while docking. Various kinds of intercom headsets are sold and these use different frequencies. There are DECT (1930MHz) headsets, wireless microphone headsets (563 MHz), and 2.4 GHz headsets that use the same frequency as Wi-Fi, Bluetooth, and ZigBee. Among these three options, if you avoid purchasing intercom headsets that list 2.4GHz as their operating frequency, this will avoid interference with these other devices on your boat.

As of 2023, boaters are experiencing interference problems with 2.4GHz devices, including devices labeled Wi-Fi, Bluetooth, and ZigBee. Note that although you can try to avoid this frequency when you buy electronics, you can’t control the boats next to you in a marina, and you may experience interference from devices you don’t own.

Some devices produce radio interference even though they are not radios: the most likely culprits are LED lights, electric motors/pumps, and the microwave oven. You can diagnose problems with these devices by noticing that interference occurs when they are switched on.

Interference with certain wireless devices is disastrous. For instance, interference with a boat controller (e.g., those made by YachtController or DockMate) could result in loss of control of the vessel. Fortunately, these devices are designed to employ frequencies that few other devices use: 433 and 916 MHz.

But many other safety-critical devices have entered the market that employ 2.4GHz wireless (often bluetooth) and appeal to the DIY boater market. These promise to use wireless to avoid the hassle of running an extra wire to the helm on your boat, or to allow you to control part of the boat with a phone app. They include engine high-temperature alarms, smart batteries/inverters, MOB alarms, bilge high-water sensors, and more. While it may seem easier to buy a wireless device than to run a new wire, check the frequencies and carefully consider the risk of interference on these bands. It may be wiser to reserve wireless features for devices that absolutely must be wireless (such as MOB devices) and otherwise spend the time to run an extra wire.

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Updated 2023-Jan-22 by Christian Sandvig, SO-CM