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Old 29-06-2006, 07:26   #1
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Screwey navigation question???

For the past few weeks another couple, myself and my wife sailed thru the Abacos on his 32' Endeavor. We had a great trip and this past week we brought the boat back to St. Augustine from the Abacos. We were crossing the Gulf Stream on Monday and were about 40 miles of off Port Canaveral at noon. We had two compasses, and two GPS. All of a sudden the compasses showed one heading while the GPS showed a completely different heading. In fact, we had been cruising at about 4.5 knots when the GPS showed us spinning in circles at .9 knots. The sun was directly overhead, so we couldn't guess east/west. We were completely confused. A freighter was approaching and we called to get their heading. We guessed they were headed south, but in fact they were headed 008 degrees, almost due North. We followed them a little to the northwest, and after about 2 hours, the GPS and the compasses were in sync again. We checked the nav maps, and the map made a comment to the effect of "A lot of space shutlle/rocket debris is in this area". We were in the middle of that area. Do you think there could have been enough metals around to mess up a compass? If so, how/why did the GPS get screwed up at the same time? What caused the problem??
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Old 29-06-2006, 07:53   #2
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You were in the Bermuda Triangle!

Check the track of your GPS. There are some weirdnesses in the currents of the gulf stream and who knows what NASA stuff may do the GPS signals.

There are other environmental cues about your cog... waves, and wind. Unless they are varying or confused they could be a clue.

You can ask a UFO for a fix!

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Old 29-06-2006, 08:01   #3
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My best guess is that you were in a fast part of the gulfstream current. You could have been going about exactly against the current, which would indicate 4.5 knots on your speed gage and near zero on your GPS.

Do you recall any change in the wind? What was your compass heading when you were going 4.5 knots?
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Old 29-06-2006, 08:06   #4
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There's a sub pen in Port Canaveral, maybe that had something to do with it. The water's too deep there for anything on the bottom to affect your compass.
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Old 29-06-2006, 12:26   #5
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Quote:
Originally Posted by Vasco
There's a sub pen in Port Canaveral, maybe that had something to do with it.
Yeah - just like there's that submerged tunnel that goes from the sub base in Bangor WA to the Navy test facility on Lake Pend Oreille at Bayview Idaho...

Both are a crock .... except in the minds of the conspiracy theorists


Vilanomark - did your wake indicate you were still sailing a straight line? Sounds to me like you were unknowingly in a slow turn that led you to believe that the freighter was headed in a direction opposite to the one you assumed.

Or it was the Bermuda Triangle effect.... maybe you could go back and find those lost planes from Flight 19??
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Old 29-06-2006, 12:51   #6
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Our wake did indicate we were going in a straight line. In fact we hadn't adjusted the throttle at all when we discovered this occurence, but the GPS showed us moving at .9 knots, and the "boat" on the GPS just spun in circles. Not quite like turning a circle, and watching your track on the GPS, but rather the boat icon just spun. Our GPS was the only speed indicator on the boat. We double/triple checked that there were no large metal objects near the compasses. We are still at a loss to explain.
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Old 29-06-2006, 21:43   #7
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Vilanomark,

More info is required. Did the GPSs have electronic compasses built in or were they simply reporting course over ground? What was the difference between the reported course on the GPSs and that on the compasses? Before and during the period in question? Was there a deviation card for either of the compasses? What's the variation in that area? I'm sure you would have indicated this, but did the chart indicate localized magnetic disturbances? Does the US Coastal Sailing Directions mention anything? I can't imagine rockets being built of ferrous material, so I doubt that has anything to do with it, but I'm sure the answer is not so simple as being "effects of the Bermuda triangle."

Kevin
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Old 30-06-2006, 06:04   #8
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When we realized the discrepency the compass showed us going south, but the GPS just spun. The GPS has a built in compass. As far as a deviation card, I would bet we didn't have one as I've never heard of one in the first place. I guess there is always more for me to learn.
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Old 30-06-2006, 06:40   #9
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Mark,

If there's a sub pen there may be submarines around. Warships often screw up civilian gps signals. Just run past the mouth of the St. John's River (Mayport) and you'll see.
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Old 30-06-2006, 06:59   #10
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If you were headed South against the Gulf Stream, it’s quite likely you were not making way over the ground (as jzk indicated earlier)cate something on the order of 3 - 5 kts (water speed), but your GPS wouldn’t detect any motion, hence no direction (of travel).
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