Humminbird 858c question

[Shine Runner]

Using Navionics Premium card, it appears lake depths are off a few feet. I noticed on the 858c menu and manual there is a map offset. The manual doesn't say what it offsets.Doh Can some one tell me what is offset and how or if I can get more accurate readings for actual lake levels vs mapping info. The lake I noticed it on the most is at normal full pool. I could understand a mapping difference if the lake were higher or lower than normal pool. Thanks.

[wannabe fisherman]

I would think that actual lake levels vary and the levels on the map are coded into the program and can't be changed ie: map levels are normal pool and actual lake level is summer pool. a few feet different

[talltimber]

Your map offset is for aligning a map point to a point on the ground (horizontal positioning adjustment). I read here a while back someone thought that their lake was mapped at a lower pool and that their depths were off. If your map is off, alignment-wise, then if you're on a ledge(by the map) you might show a significant depth difference according to your depth finder. Your map would be showing you're in one depth, when actually in another. On bigger flats it might not show that it is off much. I've scraped the bottom with the skeg, and the map show I was in 8' water, drifting out of the river channel up on a shallow flat. My lake is still at winter pool (low). What I do is adjust my shaded area to five feet or so, by the current lake level. Say, the map shows ten feet deep and the lake is five feet low. I'll shade ten feet and shallower so it will stand out on the map when I get close to five feet of water.

[Humminbird_Greg]

talltimber is right about the Map Offset menu and about changing the water depths from the Navionics map cards. There is no adjustment for the water depths shown on the Navionics mapping cards (now if it were a LakeMaster mapping card there would be, but they only cover the North-central part of the U.S.A.). I’ve heard from several who use the shaded depth feature like he has to help alert them to low water areas.

[Shine Runner]

OK. Thanks. I am a unclear on the horizontal offset though. What point am I a selecting to offset to? Hate to just try it and not mess it up and have to reset to defaults again. I like the shading tool. I have been using it to help target certain break lines to troll.