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#21
posted to rec.boats
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Driving Doglegs
"Dan Krueger" wrote in message ink.net... Gene Kearns wrote: On Mon, 26 Dec 2005 12:33:13 -0500, Wayne.B wrote: On Mon, 26 Dec 2005 00:33:08 GMT, "Butch Davis" wrote: IMO, for the gps to compute a compass course to compensate for wind and current it would have to have some means to acquire the inputs. ======================== Exactly right. Anybody know of a GPS with this capability? I'm not sure what you are trying to accomplish, but inputting wind speed and current wouldn't help since both affect different boats in different ways. A smaller, shorter boat, for example, is less affected by wind than a taller, longer boat. The purpose of a GPS is to do more than a compass. It will help you correct for wind and current if you simply use it to get to your waypoint. Dan I guess I am missing something here. Assuming the discussion is about a decent chartplotter type GPS, why all the questions about wind and drift? As I recall using the Raymarine system on my Navigator, I would transfer my planned track or route from the paper charts to the chartplotter in the morning before getting underway. The route would consist of several waypoints, usually placed in the area of a navigation buoy on the paper charts. I'd then just follow the tracks from waypoint to waypoint, either by manually steering the boat or by autopilot. If the boat marker started drifting away from the track due to wind or current, I'd see it and correct for it. The autopilot can be used in two modes. One simply steers to a course heading with no correction for wind or drift. The "Navigate" mode keeps the boat on the intended waypoint track, automatically correcting for wind or drift and automatically steering the boat to a new course as required by the waypoint settings. Worked fine for 1500 miles to Florida. So what am I missing? Eisboch |
#22
posted to rec.boats
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Driving Doglegs
On Mon, 26 Dec 2005 14:00:59 +1100, "K. Smith" wrote:
there's a further assumption that the quantum AND direction of off track forces will remain constant throughout the leg; both rarely happen. ================================= Not true. If you monitor COG vs bearing to mark and keep them equal, the "off track forces" can vary all they want, same thing if you are monitoring (and minimizing) XTE. The old fashioned way was to estimate current set over the entire leg, plot a graphical solution, and steer a constant offset. At the end of the leg you got to find out the accuracy of your estimate and calculations. With GPS you get constant feedback. |
#23
posted to rec.boats
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Driving Doglegs
On Tue, 27 Dec 2005 00:11:51 GMT, Gene Kearns
wrote: Anybody know of a GPS with this capability? ===================================== Some of the better sailboat systems like Ockam or B&G offer direct digital readout of current direction and speed. They are calculated numbers based on observing SOG vs speed through the water, and COG vs magnetic compass heading. The instrument system resolves all the vectors and spits out the numbers. It is fairly slick but requires constant calibration and cleaning of the speed sensors which are mechanical flow transducers in through hull fittings. My Furuno Navnet, integrated chart plotter/GPS/RADAR, displays a heading vector and a separate COG vector on the RADAR screen. It has an electronic compass sensor to provide heading information. Since it knows your heading, it can also overlay chart data with the RADAR data which can sometimes be useful. It needs heading information to rotate the chart into the proper orientation. I find this function particularly useful for quickly determining whether a RADAR target is a NAVAID such as a buoy, or another boat. |
#24
posted to rec.boats
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Driving Doglegs
On Mon, 26 Dec 2005 19:55:05 -0500, "Eisboch" wrote:
Worked fine for 1500 miles to Florida. So what am I missing? Nothing, that's the way most folks do it. The GPS displays COG (Course Over Ground) which is the combined effect of Boat Speed through the water, Heading, Current Speed and Current Direction, plus any set due to a crosswind. It is impossible to separate the various components without having a very sophisticated instrumentation system such as the ones that many racing sailboats carry. If you set both a "From" waypoint (sometimes done automatically), and a "To" waypoint (destination), then the GPS can also calculate XTE (CrossTrack Error). Most GPS units today can direct the autopilot to minimize XTE and thus maintain a straight course regardless of current or wind. |
#25
posted to rec.boats
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Driving Doglegs
"Wayne.B" wrote in message ... On Tue, 27 Dec 2005 00:11:51 GMT, Gene Kearns wrote: Anybody know of a GPS with this capability? ===================================== Some of the better sailboat systems like Ockam or B&G offer direct digital readout of current direction and speed. They are calculated numbers based on observing SOG vs speed through the water, and COG vs magnetic compass heading. The instrument system resolves all the vectors and spits out the numbers. It is fairly slick but requires constant calibration and cleaning of the speed sensors which are mechanical flow transducers in through hull fittings. My Furuno Navnet, integrated chart plotter/GPS/RADAR, displays a heading vector and a separate COG vector on the RADAR screen. It has an electronic compass sensor to provide heading information. Since it knows your heading, it can also overlay chart data with the RADAR data which can sometimes be useful. It needs heading information to rotate the chart into the proper orientation. I find this function particularly useful for quickly determining whether a RADAR target is a NAVAID such as a buoy, or another boat. I had very mysterious readings for a while until it was discovered that the electronic compass (I think it's called a flux gate compass) had been mounted in the engine room about 6 inches away from the electric motor for a washing machine. If I deviated more than 10 degrees off course, the boat marker would swing around so it appeared we were doing 19 knots in reverse. Another neat feature of the overlays (haven't tried it yet though) is that you can set up the Raymarine system to automatically command the autopilot to change course if the radar shows something big and solid (like another boat) on a collision course and within a programmed range. I am sure the Furuno system has something similar. I briefly had an Egg Harbor with the Furuno setup and never really learned the system. I find the Raymarine to be much more intuitive. Eisboch |
#26
posted to rec.boats
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Driving Doglegs
the original question was that if a computer (GPS) could work its magic
and do a no brains naviagtion by telling you where to steer to go from point A to B WITH cross wind/current. WITH NO MANUAL INPUT OR READING THIS PARAMETER OR THAT ERROR Simply (and only) by giving you degree where you need to point your bow. Matt |
#27
posted to rec.boats
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Driving Doglegs
wrote in message oups.com... the original question was that if a computer (GPS) could work its magic and do a no brains naviagtion by telling you where to steer to go from point A to B WITH cross wind/current. WITH NO MANUAL INPUT OR READING THIS PARAMETER OR THAT ERROR Simply (and only) by giving you degree where you need to point your bow. Matt My answer: Yes, *BUT* it may take you a hell of a long time to get there. Eisboch |
#28
posted to rec.boats
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Driving Doglegs
On Mon, 26 Dec 2005 22:07:16 -0500, "Eisboch" wrote:
the original question was that if a computer (GPS) could work its magic and do a no brains naviagtion by telling you where to steer to go from point A to B WITH cross wind/current. WITH NO MANUAL INPUT OR READING THIS PARAMETER OR THAT ERROR Simply (and only) by giving you degree where you need to point your bow. =========================== That's not a GPS, it's called a navigation computer or calculator. It will still require manual inputs, and they will be estimates at best. The question as stated is of theoretical interest only since the constraints imposed are quite artificial in the real world. In the real world your GPS will in fact tell you where to point your bow but it is a feedback mechanism, not a one shot calculation. Even NASA makes mid course corrections based on observed vs calculated. |
#29
posted to rec.boats
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Driving Doglegs
On Mon, 26 Dec 2005 20:57:02 -0500, "Eisboch" wrote:
I had very mysterious readings for a while until it was discovered that the electronic compass (I think it's called a flux gate compass) had been mounted in the engine room about 6 inches away from the electric motor for a washing machine. ========================== The flux gate sensor should be mounted as far away from iron, steel or electrical wiring as possible. I ended up putting mine in a locker where I store only life jackets. I think the Furuno user interface may have improved in recent years. I had very little difficulty teaching Mrs B how to use the target tracking functions and she is still struggling with computers and the internet. Target tracking with the ARPA functions is way cool, everybody loves it. |
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