The number of hours that you can get out of a house battery running your navigation instruments varies depending on whether you rely on shiny systems from the big manufacturers like Garmin, have a more modest system from the likes of NASA or view your data on a mobile phone or tablet.
I have the following data derived from a mixture of solar-powered Tacktick displays and transducers and powered NMEA 0183 sensors, all of which are broadcast over wifi by a multiplexer:
Apparent wind speed and direction
Position
Speed and course over ground
Depth
Sea temperature
Producing these measures and reading them only on the solar-powered Tacktick displays consumes less than 3Wh. So with a Tracer 288Wh lithium battery, I should have autonomy from shore power for at least a week’s worth of sailing. One of those small Yuasa burglar alarm AGM batteries that the yard used to supply as standard would still run the system for a full day and a bit.
The power consumption increases by a further 2Wh if the data is viewed over wifi on an iPhone (while also showing navigation charts), assuming that the phone needs recharging every now and then. If viewed on a tablet like the Sailproof 10”, the extra consumption might be as much as 10Wh. So the tablet and all the sensors could be powered by the Tracer lithium battery non-stop for two to three days.
The difference in consumption between continuously looking at this data on a big tablet or instead relying on a GPS/fishfinder from one of the big companies is not that great. For example a Garmin Echomap with a 7” screen consumes roughly the same amount of power as my system viewed over the Sailproof 10”. The difference is that out at sea, I can turn off the Sailproof screen (or swap to an iPhone) to save power and can still see all or most of the data on the Tacktick displays, whereas with a Garmin or similar, it’s all or nothing.
The advent of colour e-ink displays will significantly change all of these equations for the better, as they hardly use any power at all, especially if they do not have a high refresh rate. In the meantime, autonomy from shore power can be extended by having a spare battery, by solar charging or even by tapping into the battery of an electric outboard. The battery on my eProp outboard has over four times the capacity of my Tracer house battery. So the trade-off would be between running the power-hungry parts of the display and not increasing range anxiety by too much. With solar charging in sunnier climes, this is probably not much of an issue at all.
