If you have the garmin vhf, be prepared for some surprises if you loose gps signal either by blockage or interference.
I used to park under a metal covered roof that blocked gps signals when I found out that the vhf radio was showing erroneous gps coordinates. I went thru several experiments and analyzed the nmea2k bus communications.
Turned out the garmin 7612 in fact sent out bad coordinates like lattitude 922 degree north and 922 degree west, which as interpreted by the vhf and displayed as such, while the map display showed the proper last real coordinates on the map before I entered my slip.
I had lengthy email conversations with garmin about this “incorrect” behavior of both devices. All I tried to relay to them that the devices should be transmitting the last good known position instead of bad coordinates. If I had activated a distress call the bad coordinates would have been transmitted and rescue would not be able to use my last good position. Of course I would not call distress while in my covered slip, but I argued that if I was underway and the gps antenna were to be damaged or interfered with, I would have the same result and would not be able to rely on the accuracy of a distress call with the garmin vhf. However garmin did not see it that way and the “bug, as I call it” was still in the system. I even went to a west marine store and used one of their units to demonstrate and verify that this bug existed not only in my unit and in more than one release.
So be aware that the garmin distress system my not be reliable in certain situations