Jim: It sounds as if you maintain a watch while underway. That's the only way to go. Some folks don't. Like the guy in the rv who put it in cruise control so he could go back and make a sandwich. I used to sail on commercial cargo ships and tankers any many times i have had close calls with small boats underway with unattened helms. Safety first. John J Sent on the new Sprint Network from my Samsung Galaxy S®4. <div>-------- Original message --------</div><div>From: Jim Healy <gilwellbear@gmail.com> </div><div>Date:05/31/2015 7:32 AM (GMT-05:00) </div><div>To: raymacke@egyptian.net </div><div>Cc: great-loop@lists.trawlering.com </div><div>Subject: Re: GL: Autopilots and Bridges </div><div> </div> Hi Ray, 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? That seems a reasonable conclusion based on the way my unit behaves. That is, if the unit is following a route, it holds to a track within a few feet in calm water, and to within a few yards in 4 foot seas on the Chesapeake. But in "heading hold" mode, it is subject to the vicissitudes of set and drift, and has no ground reference to calculate XTD. Of course, XTD also relies on the accuracy of the GPS fix. If I go under a bridge and the GPS looses signal, the autopilot drops into heading hold (dead reckoning) mode; it does not disengage. It beeps to tell the helmsman it changed mode. That doesn't seem to happen often at all. If the route I'm running doesn't set me up to be directly mid-span, or if there are other boats around, I do disengage the route, but I know I have been under bridges with the autopilot in both modes. I was really careful to disengage the autopilot the first couple of years I had it, but the unit has proved itself completely reliable in operation over the years. Jim Peg and Jim Healy aboard Sanctuary, currently at Charlotte Harbor, Punta Gorda, FL http://gilwellbear.wordpress.com <http://gilwellbear.wordpress.com/> Monk 36 Hull #132 MMSI #367042570 AGLCA #3767 MTOA #3436 _______________________________________________ http://lists.trawlering.com/mailman/listinfo/great-loop_lists.trawlering.com To modify your Great-Loop subscription options (change email address, unsubscribe, etc.) go to: http://lists.trawlering.com/mailman/options/great-loop_lists.trawlering.com

Absolutely, John. If I leave the helm, Peg or another competent adult is there to keep my lookout. Even if just for a bio-break or a coffee refill. Jim > On May 31, 2015, at 07:50, johnj531 <johnj531@HOTMAIL.COM> wrote: > > Jim: > It sounds as if you maintain a watch while underway. That's the only way to go. Some folks don't. Like the guy in the rv who put it in cruise control so he could go back and make a sandwich. I used to sail on commercial cargo ships and tankers any many times i have had close calls with small boats underway with unattened helms. > > Safety first. > > John J > > Sent on the new Sprint Network from my Samsung Galaxy S®4. > > > -------- Original message -------- > From: Jim Healy > Date:05/31/2015 7:32 AM (GMT-05:00) > To: raymacke@egyptian.net > Cc: great-loop@lists.trawlering.com > Subject: Re: GL: Autopilots and Bridges > > Hi Ray, > > 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? That seems a reasonable conclusion based on the way my unit behaves. That is, if the unit is following a route, it holds to a track within a few feet in calm water, and to within a few yards in 4 foot seas on the Chesapeake. But in "heading hold" mode, it is subject to the vicissitudes of set and drift, and has no ground reference to calculate XTD. Of course, XTD also relies on the accuracy of the GPS fix. If I go under a bridge and the GPS looses signal, the autopilot drops into heading hold (dead reckoning) mode; it does not disengage. It beeps to tell the helmsman it changed mode. That doesn't seem to happen often at all. > > If the route I'm running doesn't set me up to be directly mid-span, or if there are other boats around, I do disengage the route, but I know I have been under bridges with the autopilot in both modes. I was really careful to disengage the autopilot the first couple of years I had it, but the unit has proved itself completely reliable in operation over the years. > > Jim > > Peg and Jim Healy aboard Sanctuary, currently at Charlotte Harbor, Punta Gorda, FL > http://gilwellbear.wordpress.com <http://gilwellbear.wordpress.com/> <http://gilwellbear.wordpress.com/ <http://gilwellbear.wordpress.com/>> > Monk 36 Hull #132 > MMSI #367042570 > AGLCA #3767 > MTOA #3436 > > _______________________________________________ > http://lists.trawlering.com/mailman/listinfo/great-loop_lists.trawlering.com <http://lists.trawlering.com/mailman/listinfo/great-loop_lists.trawlering.com> > > To modify your Great-Loop subscription options (change email address, > unsubscribe, etc.) go to: http://lists.trawlering.com/mailman/options/great-loop_lists.trawlering.com <http://lists.trawlering.com/mailman/options/great-loop_lists.trawlering.com> Peg and Jim Healy aboard Sanctuary, currently at Charlotte Harbor, Punta Gorda, FL http://gilwellbear.wordpress.com <http://gilwellbear.wordpress.com/> Monk 36 Hull #132 MMSI #367042570 AGLCA #3767 MTOA #3436