I got this DC-DC converter: http://cgi.ebay.com/ws/eBayISAPI.dll...412015&guest=1
The purpose was to protect my electronic equipment from turning off when I start the engines.
I connected it to my plotter, gps sensor, heading sensor and depth gauge. I have raymarine equipment which has the seatalk communication protocol. I also connected this to the converter, but have no idea of the power consumption of the seatalk system. The total amp draw from all this equipment except seatalk was less than 6 amps. When I connected it, the plotter could not obtain a fix and the depth gauge did not work. The plotter worked fine. I did not try starting the engines.
Could it be possible that the seatalk system draws so much power that the converter can't keep up. Again I never did start the engine so the converter really never was tested but it basically didn't supply enough power to power the gps and depth gauge which together draw less than half an amp.