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Old 12-09-2007, 05:43   #1
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Curse the curser

Ok confession.upon arriving mangrove key bahamas i noticed that my cursor was showing that i was onland,and not in centre of the anchorage which is where i actually was...so clever clogs here goes into advanced section of my chart plotter and adjusted said cursor to show exact position,,,big mistake ,,it was the chart that was wrong and consequently I hit the next reef and damaged my keel alot,so eyes open and leave advanced for the ones that know
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Old 12-09-2007, 07:42   #2
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If you were using a Navionics chip, I've posted extensively on this site as to how unreliable they are as far as the Bahamas goes. Their geo-referencing is way out in a lot of places. The only reliable chips are ones using Explorer Charts data such as the newest C-Maps. Even with these it's best to keep your eyes open for reefs but you know that.
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Old 12-09-2007, 08:38   #3
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Hi Rick,i was using cmap+nt..ive now got navionics but i agree lots of charts way out in bahamas..... I hit veteran rock ,bent my rudder up about 1inch,ihad to dive down and hacksaw off so that rudder would turn past hull,i have wing keel and it bent both sides up like it was ready to flap its wings ,all fixed now though,was back in 2004,
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Old 12-09-2007, 10:13   #4
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Sorry folks while the NOAA charts here in the US are pretty darn close many places in the world charts are quite poor. Many islands all over the world are grossly inaccurate by some times many miles. You always trust your eyes more than you trust the chart. GPS actually is always accurate almost any place you are but with an inaccurate chart it becomes a so what proposition. The island does not know it's in the wrong location.

I once entered a river using a very accurate chart but turned out it wasn't for the river I was in. A serious disagreement in depths turn into a "Oh, this isn't the river we want." Things need to match up to make them work properly when naviagting. I now try to make the depth match the chart and the markers match the chart and the GPS match the location on the chart all the while watching for things that might confirm my position with solid real world evidence. When things get out of alignmnet you need to revert to basics.
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Old 12-09-2007, 10:46   #5
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Reminds me of the time I ended up in the wrong harbour in the Chesapeake on my second trip south. It was blowing hard on the bay so I decided to put into Rhode River. We were sailing, dodging crab pots and trying to find marks. I finally found one and followed the marks into the "river". I had never been here before and nothing seemed to jibe with the cruising guide. I was using the waterway guide. A marina we passed had a different name, there was a lot less water than there should have been. I thought maybe the marina had changed hands and of course it had silted up a bit. We finally anchored but there was barely enough water for us. I checked the loran to see where we'd anchored. Found out we were in Galesville instead of the Rhode River! The two harbours have a common entrance from the Bay. I had got turned around trying to dodge pots and entered the wrong one. Learnt a good lesson that day on how your mind starts making things fit when they don't. The marks were not numbered the same as in the Rhode River and I told myself they must have been changed, wrong landmarks such as the marina but again I told myself that must have changed. Since then I have never tried to force fit observations to match where I'm supposed to be. Also I keep a closer eye on the compass, I should have known I was going south when I should have been going north.
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Old 12-09-2007, 10:58   #6
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Reminds me of the time I ended up in the wrong harbour in the Chesapeake on my second trip south. It was blowing hard on the bay so I decided to put into Rhode River. We were sailing, dodging crab pots and trying to find marks. I finally found one and followed the marks into the "river". I had never been here before and nothing seemed to jibe with the cruising guide. I was using the waterway guide. A marina we passed had a different name, there was a lot less water than there should have been. I thought maybe the marina had changed hands and of course it had silted up a bit. We finally anchored but there was barely enough water for us. I checked the loran to see where we'd anchored. Found out we were in Galesville instead of the Rhode River! The two harbours have a common entrance from the Bay. I had got turned around trying to dodge pots and entered the wrong one. Learnt a good lesson that day on how your mind starts making things fit when they don't. The marks were not numbered the same as in the Rhode River and I told myself they must have been changed, wrong landmarks such as the marina but again I told myself that must have changed. Since then I have never tried to force fit observations to match where I'm supposed to be. Also I keep a closer eye on the compass, I should have known I was going south when I should have been going north.
So you found the crab pot minefield at the entrance to West River, We keep our boat in Parrish Creek off West River across from the Rhode. I go into Galesville for an "at home anchorage" and usually some free wi-fi there too!
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Old 12-09-2007, 11:11   #7
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I had got turned around trying to dodge pots and entered the wrong one. Learnt a good lesson that day on how your mind starts making things fit when they don't.
It's very true you do tend to make things make sense. It's what drives insane people to do what they do. The brain will not tolerate things that don't match up. Your survival instincts won't allow it. From this it is clearly the biggest danger we all face. You'll pilot into the shoal increasing your speed all the time with confidence you are doing the exact correct thing in exactly the wrong place. You can never shut off the skills of always looking for verification of the place you are vs. where you "know" for certain you are. It is those times you will head toward the worst possible danger until the worst thing does happen.
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Old 12-09-2007, 17:53   #8
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The first rule of visual navigating is go from "big to small." Many charts will have very large costal features depicted. These include mountains, hills, towers and tall buildings.

Triangulate a couple of tall objects first, get a rough idea where you are then start looking "smaller" - piers, pontoons, marks and buoys.

Regarding chart accuracy. Well that's a good reason to approach new shores during the day.

Sorry to hear about your damage - that's sucks...
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Old 24-11-2007, 17:59   #9
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pirate This island was a moving target, but we "found" it anyway.

Back in the late 70's I was on Batwing, cruising in the Ellice and Gilbert Islands, now Tuvalu and Kiribati, and one of the Gilbert Islands had some footnotes about its location. On three different, widely separated occasions, it had been &quot;located&quot; at various positions separated by a number of miles, according to my U.S. charts. The only time we ever left the boat with no one on watch was near this island. It was dead calm, not a ripple. I climbed the mast at dusk and looked all around the horizon. No land anywhere. The next morning I awoke to &quot;Tim, Wake up! I can see the bottom!&quot; Indeed, there were coral heads everywhere, clearly visible all around us. We started the motor and steered around all of the coral heads (not being sure if they were too deep to hit,) until we couldn't see the bottom any more. We could see an island, maybe a half mile away, and we had motored away from it. Honestly, this was the only time we hadn't kept a strict 24 hour watch. It was still dead calm. This was an area of strong, unpredictable currents, not far from the equator.
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Old 25-11-2007, 08:40   #10
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...I once entered a river using a very accurate chart but turned out it wasn't for the river I was in. A serious disagreement in depths turn into a "Oh, this isn't the river we want." ...
Hey, Paul.

Let me guess--was the river on the Eastern Shore? It's not hard to get mixed up over there by relying on just your eyeballs!
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Old 25-11-2007, 10:42   #11
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Can't these chart companies do a decent sat survey and bring the charts current and accurate? Why are we relying on scanned 19th century charts???????????????
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Old 25-11-2007, 13:44   #12
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Can't these chart companies do a decent sat survey and bring the charts current and accurate? Why are we relying on scanned 19th century charts???????????????
Continuity I'd bet...

"Thats the way its always been" and some old salt somewhere might miss the island if its plotted in its correct place...
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Old 26-11-2007, 03:03   #13
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Back in the late 70's I was on Batwing, cruising in the Ellice and Gilbert Islands, now Tuvalu and Kiribati, and one of the Gilbert Islands had some footnotes about its location. On three different, widely separated occasions, it had been "located" at various positions separated by a number of miles, according to my U.S. charts...
Always refer to the Chart's "Datum" (GPS is referenced to WGS-84 or NAD-83), when plotting "position".
Differing chart datums can produce significant horizontal offsets.
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Old 26-11-2007, 11:26   #14
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pirate Floating island?

They meant compared to the other islands on the chart, not the datum for the whole chart. They even stated the date and the ship which had reported these different positions. This was in 1978, before yachts used GPS.
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Always refer to the Chart's &quot;Datum&quot; (GPS is referenced to WGS-84 or NAD-83), when plotting &quot;position&quot;.
Differing chart datums can produce significant horizontal offsets.
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