Why is my GPS not receiving signal from satellite?

The installer put the boat in the water the first day after upgrade and the system wasn't picking up satellites sitting in the slip with the motors turned on.I called Garmin and they trouble shot it over the phone and felt it could be a bad gps antenna however the tech said they rarely go bad.I re-enstalled the software and verified all version of software for each device is up to date.I fished a rockfish tournament Saturday and couldn't get satellites sitting at the dock with the motors turned on.Went fishing w no gps signal.As soon as I powered the motors to make a new drift I would lose satellites and had to repeat killing all power process.Every time I powered the motors I would lose all satellites and would not pick up a signal while the motors are on.'m not confident this is a Garmin issue Working with computers a bit, I knew to go to Garmin's website and get the latest software etc and web updater. Thank you