The Offshore Voyaging Reference Site

Instrument Loads

Seems like a lot of cruisers are leaving their instrumentation on, even when at anchor, these days.

Do what you want, but this practice could push you into a major electrical system makeover that might not be necessary if we just turned that stuff off.

The above photo shows the load (battery monitor to the right) from the instrument package and NMEA 2000 network on our J/109, added to a 9″ plotter.

Nearly two amps at 12 volts. Leave that on for 24 hours and that’s nearly 50 amp hours out of the battery!

And our system is comparatively small and miserly. Add in a big plotter, AIS, and worst off all, a laptop computer running navigation software, and we can easily burn through 100 amp hours or more.

To put that in perspective that’s over a third of the power Phyllis and I used in the run of a day for everything on our 56 foot live-aboard boat!

When left on all the time, small loads add up to big usage.

Here’s how to estimate usage and choose the right battery bank size, the easy way—no long boring spreadsheet to fill out…we provide a short, and not boring, spreadsheet.

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