I have for years been using SOB nav software
on a laptop
with the GPS
data being fed via serial-USB adaptor from an old Koden KGP-912 GPS
Part of the Koden screen
sort of misted over and it's been through 2 date changeovers (can't recall
the proper terminology here) so any date/time data attached to track points for example are nonsense. I hooked up a Garmin
GPSmap 78 I had as a spare, using the same serial-USB adaptor and attaching the old external Koden antenna
. Position data is fine but SOG and direction are erratic. If for example I'm doing a steady 6.5 to 7 knots STW the SOG displayed on the computer screen
varies every couple of seconds or so, anywhere between 4.5 to 9 knots. The course arrow emanating from ownship swings about 45 degrees either side of ahead.
Neither the Garmin
nor the SOB manual seem to address this.
Any ideas out there?