Home |
Search |
Today's Posts |
|
#1
posted to rec.boats.cruising
|
|||
|
|||
Autopilot NMEA question for gear heads
I just bought a Raymarine ST1000 Plus tiller autopilot for my Endeavour 32.
The astute among your will immediately wonder how this will work on a 13,000 pound 32 foot wheel driven boat. The unit will just drive the vane servo shaft on the Cape Horn steering gear now on order. We could have bought even a smaller tiller pilot if one was available. Since I was trying to buy the smallest and cheapest unit I could get, I was surprised to find out how sophisticated it is. Given the right NMEA input, it evidently will follow a track to a waypoint instead of just blindly maintaining a given course. It will even rollover to a new waypoint and run another leg. The Raymarine manual describes the inputs needed to follow a track but in plain English. The Garmin manual for the GPSmap 76Cx I will be using says: The following are the sentences for NMEA 0183, Version 3.01 output: Approved sentences- GPGCA GPGLL GPGSA GPGSV GPRMB GPRMC GPRTE GPVTG GPWPL GPBOD GPAPB If anyone could annotate a quoted copy of this list I would appreciate it. I've tried to find a listing via Google but the only one I can turn up is quickly replaced by another page before I can read it. Presumably, the Capt'n wants you to buy the information. A link to a similar but readable listing would also help. Any tips or experience interfacing and using one of these autopilots with a GPS also appreciated. -- Roger Long |
#2
posted to rec.boats.cruising
|
|||
|
|||
Autopilot NMEA question for gear heads
Never mind. I found a list at:
http://aprs.gids.nl/nmea/#allgp I'd still be interested in hearing about anyone's experience with such a hook up. -- Roger Long |
#3
posted to rec.boats.cruising
|
|||
|
|||
Autopilot NMEA question for gear heads
In article ,
"Roger Long" wrote: Never mind. I found a list at: http://aprs.gids.nl/nmea/#allgp I'd still be interested in hearing about anyone's experience with such a hook up. You'll love it. We have a few paths plotted that take us just to the edge of shallows we have discovered we can not cross. -- Jere Lull Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD) Xan's NEW Pages: http://web.mac.com/jerelull/iWeb/Xan/ Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/ |
#4
posted to rec.boats.cruising
|
|||
|
|||
Autopilot NMEA question for gear heads
On Thu, 1 Feb 2007 18:48:55 -0500, "Roger Long"
wrote: Never mind. I found a list at: http://aprs.gids.nl/nmea/#allgp I'd still be interested in hearing about anyone's experience with such a hook up. Most auto pilots want to know cross track error ($GPXTE), course over ground ($GPVTG) and bearing to mark ($GPBWC). I read throug the Garmin manual online and can't find any mention of cross track error. I'd call Garmin tech support. |
#5
posted to rec.boats.cruising
|
|||
|
|||
Autopilot NMEA question for gear heads
Wayne.B wrote:
On Thu, 1 Feb 2007 18:48:55 -0500, "Roger Long" wrote: Never mind. I found a list at: http://aprs.gids.nl/nmea/#allgp I'd still be interested in hearing about anyone's experience with such a hook up. Most auto pilots want to know cross track error ($GPXTE), course over ground ($GPVTG) and bearing to mark ($GPBWC). I read throug the Garmin manual online and can't find any mention of cross track error. I'd call Garmin tech support. GPRMB is what most autopilots use. It gives destination waypoint, originating waypoint, VMG to waypoint and XTE $GPRMB,A,0.66,L,003,004,4917.24,N,12309.57,W,001.3 ,052.5,000.5,V*0B A Data status A = OK, V = warning 0.66,L Cross-track error, steer Left to correct 003 Origin waypoint ID 004 Destination waypoint ID 4917.24,N Destination waypoint latitude 49 deg. 17.24 min. N 12309.57,W Destination waypoint longitude 123 deg. 09.57 min. W 001.3 Range to destination, nautical miles 052.5 Bearing to destination 000.5 Velocity towards destination, knots V Arrival alarm A = arrived, V = not arrived |
#6
posted to rec.boats.cruising
|
|||
|
|||
Autopilot NMEA question for gear heads
Ah, so these are different formats of data groups and not variables as I
thought. The ST1000 needs the cross track error to follow a track and it looks like it will get it from the GPRMB which my GPS does put out. The ST1000 manual isn't very clear but, reading between the lines, it uses either input from a speed device or a default cruising speed set in calibration to set a new course according to the cross track error. This makes me think that it doesn't take the boat back to the track but simply sets a new course directly to the waypoint. Can anyone clairify this? It also appears that, although it will roll over to the next waypoint, it won't actually turn the boat until you push the keypad. That's good if something is in the way; bad if you miss the waypoint alarm. Of course, as the manual says over and over, you should be independently tracking your position constantly. One of the thinkgs I look forward to in being able to get my hands off the wheel is to start doing a lot more navigation. All this makes me wonder. Can more sophisticated autopilots be made to follow a series of legs without intervention? If so, it's only a matter of time before someone figures out that a small ship filled with explosives could be turned into an marine guided missile. The probability is about zero since the terrorists like to blow up with their bombs and there are much more effective ways to create mahem. I have to wonder though if the people obsessed with taking away our 6 oz tubes of toothbpaste and hair gel might be coming after our navigation electronics at some point. -- Roger Long |
#7
posted to rec.boats.cruising
|
|||
|
|||
Autopilot NMEA question for gear heads
It also appears that, although it will roll over to the next waypoint, it
won't actually turn the boat until you push the keypad. That's good if something is in the way; bad if you miss the waypoint alarm. Of course, as the manual says over and over, you should be independently tracking your position constantly. One of the thinkgs I look forward to in being able to get my hands off the wheel is to start doing a lot more navigation. Getting your hands off the wheel doesn't mean no interaction with it. |
#8
posted to rec.boats.cruising
|
|||
|
|||
Autopilot NMEA question for gear heads
Roger Long wrote:
Ah, so these are different formats of data groups and not variables as I thought. The ST1000 needs the cross track error to follow a track and it looks like it will get it from the GPRMB which my GPS does put out. The ST1000 manual isn't very clear but, reading between the lines, it uses either input from a speed device or a default cruising speed set in calibration to set a new course according to the cross track error. This makes me think that it doesn't take the boat back to the track but simply sets a new course directly to the waypoint. Can anyone clairify this? It also appears that, although it will roll over to the next waypoint, it won't actually turn the boat until you push the keypad. That's good if something is in the way; bad if you miss the waypoint alarm. Of course, as the manual says over and over, you should be independently tracking your position constantly. One of the thinkgs I look forward to in being able to get my hands off the wheel is to start doing a lot more navigation. All this makes me wonder. Can more sophisticated autopilots be made to follow a series of legs without intervention? If so, it's only a matter of time before someone figures out that a small ship filled with explosives could be turned into an marine guided missile. The probability is about zero since the terrorists like to blow up with their bombs and there are much more effective ways to create mahem. I have to wonder though if the people obsessed with taking away our 6 oz tubes of toothbpaste and hair gel might be coming after our navigation electronics at some point. -- Roger Long If for some reason you get off your track, the autopilot will make a converging track to the destination waypoint. I don't know about the ST1000 but my ST4000+ has an option that can be selected to turn to the next waypoint or wait for input before turning. I selected wait for me to decide. There may be some reason I don't want to turn. krj |
#9
posted to rec.boats.cruising
|
|||
|
|||
Autopilot NMEA question for gear heads
"Roger Long" skrev i en meddelelse ... Ah, so these are different formats of data groups and not variables as I thought. The ST1000 needs the cross track error to follow a track and it looks like it will get it from the GPRMB which my GPS does put out. The ST1000 manual isn't very clear but, reading between the lines, it uses either input from a speed device or a default cruising speed set in calibration to set a new course according to the cross track error. This makes me think that it doesn't take the boat back to the track but simply sets a new course directly to the waypoint. Can anyone clairify this? SNIP -- Roger Long Unfortunately, I'm not familiar with all the NMEA codes etc. My comment is based on practical experience using a Raymarine autopilot 4000 controlling the tiller on a 34' sailboat. My experience is, that in case of XTE, the pilot "tries pretty hard to get you back to the original track" ... (not in 90 degrees toward the track though) ... but still with a course towards the next waypoint. I'm not aware of the specifik formula. On my system it is possible to reset the XTE to zero, in which case, it will make a new track to follow - i.e. from the actual position in a straight line to the next waypoint. If the system more or les automatic - i.e. without intervention - could follow another track than the original you have planned, you might get into trouble if the new track passes over a rock or other unpleasant obstacles ... I think that is the same argument/reason why the system - not without your physical intervention/approval (push a button) - will turn to the next waypont, when you are following a route. -- Flemming Torp Gimle - DEN61 |
#10
posted to rec.boats.cruising
|
|||
|
|||
Autopilot NMEA question for gear heads
On Fri, 2 Feb 2007 07:01:12 -0500, "Roger Long"
wrote: Ah, so these are different formats of data groups and not variables as I thought. The ST1000 needs the cross track error to follow a track and it looks like it will get it from the GPRMB which my GPS does put out. The ST1000 manual isn't very clear but, reading between the lines, it uses either input from a speed device or a default cruising speed set in calibration to set a new course according to the cross track error. This makes me think that it doesn't take the boat back to the track but simply sets a new course directly to the waypoint. The boat speed may be used to adjust the rudder response - I don't recall any mention of a speed input on my ST5000. From observing the operation of my ST5000 and an earlier tiller pilot, when you first select "Steer by GPS", the pilot will look at the "bearing to waypoint" reported by the GPS, and will set that bearing as the desired course, and turn the boat to that direction. Once the boat is on that heading, the pilot will ignore the "bearing to waypoint", and instead start watching the cross-track error (xte). If the GPS reports that the xte is to the left of the desired track, the pilot will adjust the course to steer slightly to the right. If the vessel remains off-course to the left, the pilot will make larger adjustments, until the boat is back on the desired track. If it overshoots, and gets to the right of the desired track, the pilot will then adjust the desired heading slightly to the left. The result is that the boat will remain as close as possible to the track from the origin waypoint (or from where you told the GPS "GoTo Waypoint) to the destination waypoint. There are a couple of situations where having the autopilot follow GPS instruction can be undesirable - but they are situations where the navigator should take special steps under any situation. One such situation is crossing a strong current (Gulf Stream, perhaps) in a slow boat. If the current is faster than the boat, the autopilot, in an effort to minimize XTE, will eventually have the boat headed directly upstream, and making no way across the stream - this is Not Good! Without the GPS, the prudent navigator would probably head somewhat upstream before entering the strong current, expecting the current to carry him downstream towards his destination. Having a GPS and autopilot does not free the navigator from understanding, and dealing with, such situations. Can anyone clairify this? It also appears that, although it will roll over to the next waypoint, it won't actually turn the boat until you push the keypad. That's good if something is in the way; bad if you miss the waypoint alarm. Of course, as the manual says over and over, you should be independently tracking your position constantly. One of the thinkgs I look forward to in being able to get my hands off the wheel is to start doing a lot more navigation. My GPS and plotting programs, as well as the autopilot, will alarm on arriving at a waypoint. I consider this a Good Thing, as I don't want the boat to automatically turn into the path of another vessel. It appears that the Raymarine pilots look at the destination waypoint name in the RMB sentence to determine when a new leg starts - I was beta-testing a chart program that didn't put the waypoint name in the RMB sentence, so the autopilot had to watch the xte to change to the new course - this resulted in excessive overshoot before we got back to the desired new heading. -- Peter Bennett, VE7CEI peterbb4 (at) interchange.ubc.ca new newsgroup users info : http://vancouver-webpages.com/nnq GPS and NMEA info: http://vancouver-webpages.com/peter Vancouver Power Squadron: http://vancouver.powersquadron.ca |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Cheap navigation system | ASA | |||
Volvo Question, putting MDIIB heads on a MD11C? | Cruising | |||
Question on autopilot | Electronics |