2 dead on Barkley

[the_donger]

At about 3am Thursday morning a 21 foot bass boat with five people in it crashed into some rocks, killing two and injuring the other three, one of whom is still unconsious. This accident comes less than a month after a jetskier was killed after hitting rocks by the Quarry on Kentucky Lake. Be careful out there guys. I may not know you, but I still care.

[dcbasser]

I'm hearing you. Seems like this year has been the worst that I can remember for accidents. I fish a local tournament on tuesday nights with about 25 boats not counting the other two that go on. Had several encounters that were closer than I like. Seems that as big as fishing has gotten and the number of tournaments going on especially at night that folks are getting to comfortable with their watercrafts whatever that may be. Seen to many close calls this year for my taste. With the 4th coming up I'm sure the lakes will be even more crowded and a lot more opportunities to take place so be careful out there.

[artcarney_agr]

I heard a little more info about the wreck. The boat driver survived, and he was the one that had to get help and pulled people out of the water. The accident actually happened at 12:00 or 12:15. He said his navigation system (GPS) malfunctioned and was the reason he hit the rocks.

Kind of makes you think twice about relying solely on technology.

[fishbum]

At best GPS is around 3 feet off. BUT it can be as much as 100 Yards. This depends on the system and on the WAAS Land Towers staying operational ( Land towers mark the drift of the satellites as their orbit can be off). IF they go down the drift of the Satellites can be off. Weather can affect these land based towers as well I would imagine. That weather could be in New England or Texas Depending on where the Towers are that help the Satellites to transmit their signals..

[Downwind]

Something to remember about GPS. It's set up for travel as the crow flies, It doesn't know if there is anything in between, (say an island). Tha's why it's important to have a map to go along with the use of a GPS.

[peter]

Seems to be a common error. People think GPS is radar and it is not. Be careful.

Peter

[MASBASS]

I am a surveyor and have worked with GPS for over 15 years. GPS is a good TOOL but that is all do not bet your boat or LIFE on it. The grade of GPS that we place on our boats and cars is not as accurate as what is used to survey with but they are still accurate on average of 3-6 feet in perfect conditions. According to Garmin, this is from their web site "A WAAS-capable receiver can give you a position accuracy of better than three meters 95 percent of the time." people that is 9.84 feet. So IMO it would be silly to use a GPS/mapping unit to run down the lake if you can not see where you are or do not know where you are. It does not matter if it is a mapping unit or not you best not trust it too far.

The most common problem that causes GPS to give bad information is not weather, FISHBUM I am not trying to disagree with you I always value your opinion, it is misuse of the unit or a misunderstanding of how GPS works. I do not know how many people have told me how accurate they can navigate with their GPS units. I believe they can most of the time but what about that few times you can not.

A couple of things to remember when using GPS is this. The secret to accurate positions with a GPS unit is an open sky no trees, cliffs, boat windshields, fish finders or body parts above antenna. The more satellites you receive and the more spread out they are the better your positions will be. If the signal is blocked or bouncing off of you or your boat windshield your positions will go from 5 feet to 30 feet in a couple of seconds. Garmin has some good information here is a good web site http://www.garmin.com/aboutGPS/ that can help understand how they work.

[artcarney_agr]

I know just what you mean MASBASS. I've used Trimble's GPS units for mapping and setting reference points on site surveys. Like you said, vertical obstructions affect GPS performance. Running a boat under a bridge is a quick way for a satellite to lose signal with your receiver. I'm not sure of the exact location of the accident, but I know there is a bridge in Little River in the area of the accident. Do you think it's possible he went under the bridge, lost signal, and before it came back online he ran into the rock wall? The tall vertical wall with trees on it may have also blocked the satellite signal.

I also remember from surveying class that there is a time of day when there is only a few of the satellites visible in the sky due to the earth's rotation. Could it be that at around midnight the number of visible satellites was at a minimum?

[MASBASS]

A bridge would only cause a few seconds problem, a vertical wall could very easily be a major problem. You not only take 40%-50% of possible sky you also create a Multi-path problem. Multi- path thinks the unit is still locked in good position but in fact the fraction of a second delay in the signal can cause major position error. 50-100 feet easy. There is no way to know for sure. I just know that there are several possible problems and all but one is human created, solar flares can cause some major problems. The only time I had problems with weather conditions one time it was when I had about 4" of snow on my antenna. It is terrible about the accident, that is why IMO anyone would be extrememly foolish to navigate in our lakes around here using only GPS or relying soley on them, there are too many factors that can cause problems. The biggest factor being human involvement. How they work is an exact science how people use them is not.

[artcarney_agr]

Well put MASBASS.

[Danny]

I'm confused by the statement about the statelites being out of view. I always thought the satellites were in geosynchriness orbit. Is that not right?

And please forgive my poor spelling. My dog seems to think she needs to be in my lap while I'm typing. LOL\

At least someone loves me, besides my wife.

Danny

[artcarney_agr]

Danny,

Here's a clip that I cut from an article on Satellites and GPS navigation that should answer your question:

.....The last major issue was the altitude of the GPS satellite constellation. Satellites are generally either placed in low Earth orbit, a few hundred kilometers high, or in geostationary orbit over the equator, 36,000 kilometers high, where they take 24 hours to orbit the Earth and remain in a fixed position relative to the Earth as it turns under them.

Putting the satellites into low Earth orbit would reduce the size and cost of the boosters required to launch them, and would also reduce the power required for the transmitters on the satellites. However, obtaining adequate coverage would demand a large number of satellites. Putting them into geosynchronous orbit would reduce the number of satellites, but it would require more powerful launchers and transmitters, and it would not provide good coverage of the polar regions.

The altitude finally chosen was a compromise: a circular orbit with an altitude of 20,200 kilometers and a period of 12 hours. At that altitude, 17 satellites would be enough to make sure that four of them, the minimum number needed to establish a position, would always be visible from any location on the Earth's surface.

The GPS constellation finally implemented actually has 24 satellites, consisting of 21 in active operation, plus three spares. The 24 satellites operate in six different orbital "planes" (an orbital path shared by multiple satellites), with four satellites in each plane. The planes are inclined 55 degrees with respect to the equator. The GPS satellites are also fitted with nuclear blast detectors as a secondary mission, replacing the early "Vela" nuclear blast surveillance satellites in this role.