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Use your charts with a grain of salt.
http://www.goupstate.com/apps/pbcs.d...60/1051/NEWS01
Not that any of us will be cruising at 30 knots 500 feet below the surface but navigating soly by GPS you are just as blind. Many of the charts we use are from surveys over 100 years old. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
On Sun, 16 Jan 2005 11:04:38 -0500, "Glenn Ashmore"
wrote: http://www.goupstate.com/apps/pbcs.d...60/1051/NEWS01 Not that any of us will be cruising at 30 knots 500 feet below the surface but navigating soly by GPS you are just as blind. Many of the charts we use are from surveys over 100 years old. Indeed. I was looking at some Softcharts of SW Carribean last night. I loaded up some GPS tracks captured in the area and was unsurprised to see a track pass through the middle of a sizable island. It's an interesting situation. The government cartographic agencies trust a century old report from a vessel that may not have gotten a celestial fix in days, but not a solid GPS fix from a yachtsman. I've often wondered whether it would be feasible to implement a public or private program for vessels to have their instrument suites validated and a way for them to upload the data to a central authority. With enough reports from a given area, said authority would then apply statistical techniques to validate the data. For instance, my cpRepeater program captures water depth, temp, and position (among other things) and logs them. I could easily add something like an MD5 algorithm to digitally sign the log, proving that it has not been altered. That would suffice for soundings. A snapshot of a radar display would locate shorelines precisely. The analysis would be tricky: apply celestial tide state, smooth the results, look for outliers in the data, decide whether the resultant confidence level in the data is sufficient for navigational use. __________________________________________________ __________ Glen "Wiley" Wilson usenet1 SPAMNIX at world wide wiley dot com To reply, lose the capitals and do the obvious. Take a look at cpRepeater, my NMEA data integrator, repeater, and logger at http://www.worldwidewiley.com/ |
"Glenn Ashmore" wrote in message news:mgwGd.21097$EG1.17828@lakeread04... http://www.goupstate.com/apps/pbcs.d...60/1051/NEWS01 Not that any of us will be cruising at 30 knots 500 feet below the surface but navigating soly by GPS you are just as blind. Many of the charts we use are from surveys over 100 years old. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com What do you recommend instead of GPS Glenn? Postulate a mountain top three feet below the water surface. Not charted. I doubt that inertial or celestial would offer any protection. Face it...every once in the while the Gods **** on our pillar. Jim Donohue |
Yeah, the QEII (I think) ran aground about 20 years ago just off the
Elizabeth Islands on Cape Cod and in one of the most heavily traveled areas of New England. The chart turned out to be wrong. -- Roger Long "Glenn Ashmore" wrote in message news:mgwGd.21097$EG1.17828@lakeread04... http://www.goupstate.com/apps/pbcs.d...60/1051/NEWS01 Not that any of us will be cruising at 30 knots 500 feet below the surface but navigating soly by GPS you are just as blind. Many of the charts we use are from surveys over 100 years old. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com |
It's not so much you should use your charts with a "grain of salt", as
you need be aware that they are not perfect and if you have any doubts, you should use ALL means at your disposal, especially the "Mark I eyeball". If you see discolored water, obvious current swirls, disturbed wave action, (to name some) in a particular area, or your wake changes and you bog down ..... these are indications that something may not be as the chart suggest, and it doesn't matter whether you're using GPS, celestial, radar, etc., for your navigation, you may want to stop or reverse direction till you can figure things out or find a better route. otn |
I'd be happy with something simpler: allowing me to update my own maps.
IOW, I'd like to be able to import my own depth soundings into electronic charts that I use. Does any such thing exist? I'm a big Chesapeake gunkholer and a record of my soundings, synced with tides would be very useful. -- 01/16/05 17:54 |
Yeah, the QEII (I think) ran aground about 20 years ago just off the
Elizabeth Islands on Cape Cod and in one of the most heavily traveled areas of New England. The chart turned out to be wrong. Is that the case? I heard about something similar but not a case of a chart being wrong. A cruise liner enroute to Boston was under autopilot but the gps lost lock for an extended period of time. During that period the course was continued with the unit doing its own dead reckoning. By the time it regained lock it was well off course and the new course to the next waypoint took it over some rocks. None of the crew had noticed the system had lost lock and all were trusting that the "gps referenced autopilot" was safely steering the ship waypoint to waypoint. They also did not bother to look and see that their course was now taking them over the rocks. |
That rings a bell and I think you might be right. The shoal being
shallower than charted may have been a secondary factor. I don't think it would have been GPS in those days. Probably Loran. -- Roger Long wrote in message .. . Yeah, the QEII (I think) ran aground about 20 years ago just off the Elizabeth Islands on Cape Cod and in one of the most heavily traveled areas of New England. The chart turned out to be wrong. Is that the case? I heard about something similar but not a case of a chart being wrong. A cruise liner enroute to Boston was under autopilot but the gps lost lock for an extended period of time. During that period the course was continued with the unit doing its own dead reckoning. By the time it regained lock it was well off course and the new course to the next waypoint took it over some rocks. None of the crew had noticed the system had lost lock and all were trusting that the "gps referenced autopilot" was safely steering the ship waypoint to waypoint. They also did not bother to look and see that their course was now taking them over the rocks. |
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