I am wondering where they got the higher definition hydrology data from?
Someone had to map the bottom with sonar and the only one that I know of that has spent the time doing that is Pat Hahs of Kentucky Hydrografx.
Pat sells his data to fisherman on CD. I have wondered if Nav purchased any of Pat's data?
Pat has side scanned a lot of KY lake's bays and areas but not all of the lake. His side scanning data is combined with his hydro-data and laid over a map view of sections of the lake
Pat's map are probably accurate to plus or minus 10 ft as that's the limits of his GPS unit that he uses to determine his position while he is taking a depth sounding. So the latitude and longitude are always going to be off by plus or minus 3 meter about 95% of the time. The depth measurements are accurate to about 4". He claims that getting multiple readings corrects for the longitude and latitude errors but I discount that. Still his maps are much more accurate than any other map and I would highly recommend that people wanting to catch fish on sections of KY lake that he has mapped buy his products.
Now maybe the Government has remapped KY lake but I doubt that. Most of the USGS 7.5 Topo maps were made using stereoscopic views and side by side aerial photographs of the KY lake area before the lake was damned up.
Modern Satellites could remap the lakes bottom if they could see it. I am thinking that the US Military can use it's spy satellites and super computer to get a true 3 d view of any land on earth these days. That's how they get the topographical data of foreign lands that's used by our cruise missiles.
So until you know where the new data for Navronics comes from you won't really know the accuracy of the data.
KY lake and other lakes with river flowing though them are going to be silted in in some spots and washed away in other spots over the decades. KY lake was formed in the 1940's so it's had 70 plus years to change.
My suggestion for the best way to fish KY lake with hydro-graphic type maps is to get the section of lake you wish to fish from www.kentuckyhydrografx.com and then get a small laptop computer along with the full version of a program called OziExplorer and then use that to figure out where you want to fish. Get the GPS longitude and latitude of the spots you wish to fish or make routes to each spot so that you can plan out the entire days fishing. Then use a gps unit to get to those spots. To really get on the right spots get a Humminbird side scanning sonar and use it to zoom in on some brush piles on these spots. Knowing the water temp you can figure out the depth of the fish and concentrate on those depths that match up with the lake contours and cover.
Make sure that your gps map datum matches the paper map or digital maps datums. This is CRITICAL. The earth not being perfectly round makes calculating your position on earth much more difficult. So the Datum used determines how accurate your gps will be compared to a paper map or digital map. If you use one map datum on your gps setup and the paper map uses a different map datum then your accuracy will really suffer. You can be off by 100 yards in some spots.
Nads 27 or NADS48 are two of the most common map datums used these days on our fishing maps.
I have the 2003 MapSource Fishing Hot Spot Digital Maps for KY Lake. These digital maps are loaded from a CD onto my computer than uploaded to my Garmin GPS hand held eTrex Vista unit. These maps have some icons on the display that are suppose to show were the Corps or KY DNR put in brush piles. I found that the location of the brush pile on my digital map was off by a few tens of yards. I though it was due to the different map datum but I checked that and all was OK there. It was just that they didn't mark the spot right. I eventually found a brush pile nearby but it was over 50 yards away. I was in map view and my boat's icon was sitting right over the brush pile icon. I looked around and had gone around in ever increasing circles around this icon on the map but could not located the brush pile that was suppose to be there. NOW GPS units are only accurate to plus of minus 3 meter 95% of the time. I found the brush pile by watching the water and noticing a turtle surfacing and then diving back down. I moved the boat over to where I saw the turtle and found the brush pile right there. My digital map had the brush pile in the wrong location. The map was off by about 50 yards.
Moral of the story is those digital maps are not always right on the money. They can be off by 50 yards in some cases.
I had the same thing happen to me on Patoka Lake. There is a fish attractor on Patoka Lake that I have never been able to find. I know the map location as I have it on my digital map of Patoka Lake on my eTrex Vista gps and I have it on my FHS map on my computer. I can see the longitude and latitude of this spot on my computer screen when I move the mouse cursor over the spot on the map on my screen.
But when I am out on the lake and use my map view to get my boat over this fishing spot I can't find the structure on my Depth finder. I am sure that there is a bunch of big tree trunks (logs) chained together some were in this area but I have yet to find it. But I found brush that grew along a series of ditches in this area which holds tons of crappie. So I never really had to find the deeper brush pile as I was too busy catching fish in the 15 ft depths. I found that it's true that the fish come out of the river and into the creeks and then follow the ditches to the shallow water areas. I found on spot with the help of my buddy where the distance from the river to the back end of the ditches is not more than 200 yard to 300 yards. So the fish are easier to find. Start out in the deep water and move toward the shallows until you make contact with the fish or vis versa. The fish are there almost year round. But the change their location and migrated from the deep water to the shallows and back again depending on the weather. Water temperatures, currents and the amount of light that penetrates the water are keys to finding these fish.
Originally Posted by R19
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