Tuesday, November 27, 2007, 7:15:06 AM, Peter wrote: >> After all the posts on AUTO vs NAV and reconsiling my own operation, > I PG> feel I have to make the following somewhat counter opinion to the > trend of the discussion.>> > NAV is simply an XTE corrected and end of course alarmed AUTO, so if >> AUTO is okay, NAV is essentially a more accurate attempt at the same >> goal. So do we need to always hand steer? PG> I'd suggest that NAV mode is inherently safer than AUTO. However many skippers PG> punch in waypoints at points where course changes should be made and at the PG> destination point. If these points are far apart, Xtrak error (in degrees) can PG> lead to problems. You can have a Xtrak error of 1 mile, that is still only 2 PG> degrees if the next waypoint is 30 miles off. Breaking the route into smaller PG> chunks of 1/2 hour segments, even if that means 20 waypoints on a straight PG> line course for a day's cruising, will keep a tighter course if set, drift and PG> wind will play a factor. Cross-track error is the _distance_ that you are off the intended track, not a bearing to the distant waypoint, so there is no need to break long straight tracks into shorter segments. When the autopilot is in NAV mode, and following the GPS XTE instructions, it _will_ automatically compensate for set, drift, or leeway by adjusting the vessel heading to minimize XTE. -- Peter Bennett, VE7CEI Vancouver, B.C., Canada Ennos 31 "Honeycomb" GPS and NMEA info: http://vancouver-webpages.com/peter Vancouver Power Squadron: http://vancouver.powersquadron.ca

Peter Lets start an off line exchange Peter> Date: Tue, 27 Nov 2007 17:47:00 -0800> From: peterbb4@interchange.ubc.ca> Subject: Re: T&T: NAV Mode and Autopilots> To: petergelinas@hotmail.com; trawlers-and-trawlering@lists.samurai.com> > > > Tuesday, November 27, 2007, 7:15:06 AM, Peter wrote:> > >> After all the posts on AUTO vs NAV and reconsiling my own operation, > I> PG> feel I have to make the following somewhat counter opinion to the > trend of> the discussion.>> > NAV is simply an XTE corrected and end of course alarmed> AUTO, so if >> AUTO is okay, NAV is essentially a more accurate attempt at the> same >> goal. So do we need to always hand steer?> PG> I'd suggest that NAV mode is inherently safer than AUTO. However many skippers> PG> punch in waypoints at points where course changes should be made and at the> PG> destination point. If these points are far apart, Xtrak error (in degrees) can> PG> lead to problems. You can have a Xtrak error of 1 mile, that is still only 2> PG> degrees if the next waypoint is 30 miles off. Breaking the route into smaller> PG> chunks of 1/2 hour segments, even if that means 20 waypoints on a straight> PG> line course for a day's cruising, will keep a tighter course if set, drift and> PG> wind will play a factor.> > Cross-track error is the _distance_ that you are off the intended> track, not a bearing to the distant waypoint, so there is no need to> break long straight tracks into shorter segments.> > When the autopilot is in NAV mode, and following the GPS XTE> instructions, it _will_ automatically compensate for set, drift, or> leeway by adjusting the vessel heading to minimize XTE.> > -- > Peter Bennett, VE7CEI Vancouver, B.C., Canada> Ennos 31 "Honeycomb"> GPS and NMEA info: http://vancouver-webpages.com/peter > Vancouver Power Squadron: http://vancouver.powersquadron.ca> _________________________________________________________________ Are you ready for Windows Live Messenger Beta 8.5 ? Get the latest for free today! http://entertainment.sympatico.msn.ca/WindowsLiveMessenger