Autopiloting by Chartplotter

[jbondy]

I have a Raymarine chartplotter/GPS and the S1 Wheelpilot. I often like to plot my course for the day in advance and save it as a route, with the expectation rthat doing so will help me get there. But there are several problems with this.

First, when following a course, one often has to avoid an obstacle, e.g. a lobster pot buoy or fishing boat, which I do by steering around it using the S1 control head to steer, as recommended by Raymarine. When I re-engage track mode, the boat will steer sharply to get back onto the track. For example, if I steered to the left to avoid the obstacle, the pilot will steer sharply to the right to get back to the track and sharply to the left to follow the track to the next waypoint. It defines a line that the boat will follow and it gets back on the line instead of simply aiming at the next waypoint, thereby creating a new line. This causes a problem when under sail. The sail adjustments to avoid the obstacle and point to the waypoint are usually pretty small. Last weekend, when the autopilot was trying to get me back on track, it would have caused two quick jibes.

I asked Raymarine if there was a way to easily set a new track within the course to the next waypoint. There response was, "I am afraid not unless you ask the chart plotter to recalculate XTE and then the boat must be within 60 feet of the 'NEW' track line."

A related problem is when sailing to a waypoint that is dead upwind. Once the track to a waypoint is calculated, it always shows the adjustment needed to get back on the track, not to get to the waypoint. I, for one, find this needlessly confusing. I don't expect it to tack for me, but to be able to show me the direction I need to go to get to where I'm trying to go, as opposed to get onto a track that would have taken e there from my original starting point, would be much more useful.

When on a multiple waypoint course, I'd like to be able to continue that course (not necessarily by getting back on the predetermined track) and not stop it and recreate a new course. I could simply set the waypoints and not make a route of them. Then I would continually be using the menus to "go to a waypoint". But that seems to forego an opportunity to allow computerized tracking to assist in navigation.

Is this problem unique to Raymarine? I'd be interested in hearing others' comments.

TIA

[Vasco]

When on a route and we get off due to a course change to avoid whatever we just reset the XTE and put it back on track. Quite easily done. I don't understand what problem you're having. You still get to the waypoint and continue on your route.

[jbondy]

Vasco - Thanks. How does one reset the XTE? Is that what Raymarine meant when they said to "ask the chart plotter to recalculate the XTE"? What about their statement that "then the boat must be within 60 feet of the 'NEW' track line"? Does that mnean you can only do this if you're still close? Finally, would this work when tacking to a waypoint. i.e. recalculate the XTE after every tack?

Sorry for all the questions. I guess I'm not getting how XTE works. But thanks.

[speciald]

I don't know whatr series you have but on the RL series - when following a route - hit the go-to button, then hit retart XTE.

[tweitz]

The reason the chartplotter behaves the way it does is that you may not always want to go straight to the next waypoint when you have turned off course to avoid an obstacle. If the course you have laid is designed to avoid other obstacles or shoals, you would not want to hit another obstacle just because you have avoided the first one. I personally have never activated the routing function integrated with the autopilot, because, on a sailboat, I need to know to be involved when we are making a turn to be ready to adjust the sails. Even under power, I am uncomfortable with trusting the autopilot quite that much. I am more than happy using it when on a straight course.

[jbondy]

Thanks. I must have been brain dead when reading the manual, but I didn't get XTE at all. Now I got it!

I don't trust the autopilot to steer the entire route, just to keep me on track between waypoints. It frees me up to adjust sails and leave the crew alone. I wouldn't let it make a turn automatically any more than I liked the idea of it taking over to get me back on track. (The C80 sounds alarm when you reach a waypoint but does nort make a turn unless you tell it to.) But I do like planning the entire trip in advance and putting the waypoints into the plotter. My silly XTE blind spot was keeping me from being able to take advantage of it.

Anyway, thanks, all.

[Valiente]

I have a lot of suspicions surrounding using an autopilot in this fashion, although I suppose if you are keeping a good watch it's fine.

I prefer the idea of setting a waypoint based on the most favourable wind that will least tax the autopilot and is clear of known obstacles. This means a compass bearing only; my cross track on the plotter or via simple chart work informs me of current sets, drift and other information I want to understand and observe. In other words, I deliberately "dumb it down" to save power and to throw the presence of currents into obvious relief.

Basically, if I treat the autopilot like an electric windvane, I am working in concert with the prevailing conditions, and not just getting to an artificial waypoint with the least extraneous movement. If you have to disengage the pilot to steer, you can simply return to the compass bearing (already known) before re-engaging the pilot...most of us can do that within 5-10 degrees...and then you aren't going to "lurch" or slat your sails because your boat is "perceiving" that it is inexplicably wildly off course.

Offshore, it would be all windvane, unless I was purely motoring, and even then, it might be a shockcord/rope lashing on the tiller.

[sailboy21]

I have had similar problems using the S1 with Chart navigator on a laptop. The corrections would be so dramatic that the helm would be put hard over and then again when the AP overshot the lay line. To further aggravate the situation, not pressing the "auto" immediately button when arriving at the next way point would cause course changes just in excess of 90 degrees. Good thing I am not the editor of any sailing mag or the S1 would get the "Worst Autopilot Ever" award. Maybe I am just biased since my first wheel drive self destructed after a week and a half in the middle of the night during a 36 hour passage..

[Valiente]

Well, that's another issue in favour of not letting the pilot "resume course" when it takes a minute or so to point the boat manually and then hit "autopilot".

I have noticed this on other peoples' boats: a really unpleasant swerving until the pilot can figure out where it is. Can't be good for the equipment.

[xort]

I look at the plotter and run the cursor out to the place I want to go and take note of the bearing it gives. I then steer onto that bearing with the compass, verify the compass reading matches the gps heading and engage the autopilot. If I have to make course changes, I do that routine all over again looking at the 'new' route to see if I've added obstacles that need to be dealt with. Every so often, say 15 to 30 minutes and sometimes longer, I disengage autopilot and hand steer to verify everything feels right and to give the autopilot a break.