<John wrote: What you say is correct, maybe he was trying overcome what I realize as a shortcoming in my design.> I'd be careful to make sure that you meet the Furuno requirements for the compass GPS'S. They need a clear view of the sky in order to get the accuracy to resolve the location fine enough to give a heading reference. If they are shaded even a little bit you'll have heading jitter when the number of birds in view is less than optimum, IMHO. This is not as critical for the nav gps's as an error of a inch or two in computed location doesn't really matter. To me it is astounding that one can expect to resolve the location difference between two GPS receivers 18" or so apart accurately enough to determine the static heading. This is quite a feat, IMHO. OTH, because of this one should always realize that it can and will on occasion give a bogus heading. Local EMF disturbances, intentional falseing of the GPS signals, and/or other failures in the data acquisition/computational process. This is why a GMDSS system requires the gyro compass as a part of a proper system........I think. It will smooth the small inaccuracies from the GPS while the GPS keep the long term drift of the gyro in check. As always YMMV..... Cheers Dave & Nancy Swan Song Roughwater 58 Caribbean Cruise '07