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On-board noise

There are many sources of noise on board a boat. Once the motor is off and the boat is under sail, things quiet down. Most of us don’t actively think of noises on the boat unless they become worrisome or annoying. The crew can be the most immediately annoying, especially if they don’t like the provender and drink in the galley (or cooler, depending on your boat). However, there is a type of noise that many sailors don’t think about that can adversely affect the operation of the boat: electrical noise.

How do you know that there is electrical noise? It’s usually noticed first on anything to do with audio, so the radios are the first place that electrical noise gets noticed. There might be a hum on the stereo, or whistling on the VHF, or buzzing on the SSB. But there are other places that electrical noise can cause problems. One common place on the Ockam system is the boat speed reading – especially on the 015 “black box” type interface. Electrical noise can cause all sorts of silly values here. Another place is the wind speed; the value for wind speed usually just stays put at or above a particular value if there is a noise problem. I’ve seen a boat with wind speed stuck at 52 knots because of AC induction from an inverter.

Electrical noise is typically only noticed when it starts affecting the normal operation of the boat’s electronics, but it’s almost always present to one degree or another. If you suspect there is a problem, you can try a few things to isolate the source.

First, turn off any generators and inverters. Also turn off any battery chargers. Finally, disconnect any shore power or communication connections (cable TV, telephone, etc.). These are very common sources of electrical noise. If the bad behavior goes away once you have removed these potential sources, then you know that one of them is likely responsible for the noise. Re-attach or turn them on one by one to see when the bad behavior comes back; you should be able to figure out the source.

But what to do about it? In some cases, simply providing a good ground connection can solve your problems. There are also a variety of noise filters available to help remove noise from the voltage supply of a boat. I have found that good battery isolation between banks (again, there are a variety of products that do this) can help immensely, especially on boats that use more than one house bank.

The Ockam system can also be a source of noise, especially the older systems operating with an SSB on the boat. The paper at this link covers several strategies to eliminate this noise. I have found that most boats don’t even get past the first two remedies before the problem is reduced to a level where it is no longer a problem. On the newer systems, the components produce far less electrical noise, so reduction of RFI is rarely an issue.

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