Preliminary tests show that combined power consumption of Raspberry Pi 4 based boat computer and Argonaut M7 gen2 7-inch touch display stays under 10 watts. If I turn off the display then wattage drops to 4-4.5 watts. If I reduce the brightness on the display backlight it drops dramatically as well. So both display and Pi contribute about the same share in power consumption. On average I see their combined draw of 0.75 amps at 12v (about 9 watts). This is with 2 chained USB hubs and long wires (HDMI/USB/power) between a computer and cockpit display and hub, AIS (dAISy), RTL-SDR (plugged in but idling), Flashdrive SSD, FTDI (connected only into USB).

10 watts on 80 amp-hours 12v battery (in my understanding they are rated for that before drop below 10v, so it is all usable amps) will give you approximately 80*12/10=96 hours of chartplotting at max brightness. C’est la vie. That’s why you need solar panels on your sailboat.

While experimenting with power usage and connecting/disconnecting various USB devices and Argonaut M7 to different USB ports and hubs (USB2, USB3) Argonaut M7 became unresponsive. Even its own power on/off button didn’t work. I had to perform a factory reset of it.

The reset procedure as per manufacturer requires to hold power button on Argonaut M7 display immediately after full power off/on cycle. On my boat it’s really a two-man job then. There is no power switch in cockpit because the M7 display has its own and the other switch to power it on is below deck. It seems they didn’t think about single handed sailors when they came up with this reset procedure design.

Turns out if I turn off 12v supply into cockpit it does turn-off the display but it’s LED status light still stays on. So it still gets some power via USB (not much per amp meter). Apparently this is the default behavior of most self powered USB hubs to draw from the host when they lose own power supply. There are some hubs which have this behavior configured by a jumper on their PCB, but the default is to power itself from the host.

I did test fiber-optic USB data cable leading to the cockpit as well. It does have regular wires for power as well, so it behaves exactly the same. The cable is much thinner so you can have a smaller hole is your boat in a cockpit deck.

Reboot doesn’t work. It just shuts down Pi. There are many reports that pi4 doesn’t reboot with USB self powered hubs if they are not powered off before the reboot and backfeed power into Pi. So currently the reboot procedures are shutdown and then power cycle the boat computer.