The main reason that "route follow" generally will not exhibit the Crazy Ivan swing while passing under a bridge is that it is based on GPS heading info and not magnetic compass info. As long as the GPS holds a "fix" it will not be affected by the bridge and with so many satellites in view these days and 12 or more channel GPS receivers; there are not too many loss of fix encounters any more. Heading hold is often (but not always) utilizing the fluxgate compass. My NavMan (now NorthStar) autopilot can select either "COMPASS" mode or "GPS" mode for the "Heading Hold" function, but the default is the fluxgate magnetic compass. Ken Bloomfield MTOA 2062 AGLCA 3529 On 5/31/2015 11:59 PM, great-loop-request@lists.trawlering.com wrote: > My autopilot has two operating modes: "heading hold" and "route follow" are the terms used in my unit's user guide. I use both, but for bridges and long canals and such, am usually in "route follow" mode. I have a Garmin GHP10 autopilot, and have never seen the Crazy Ivan behavior you describe. I'm not certain, but I wonder if the course computer uses XTD in "route follow" mode rather than the course heading for the route segment? --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com