Navionics cars in lowrance unit

How often do you need to update and or get a new card? I’ve been noticing the topo lines don’t match up to the depth I’m showing on sonar and everything else. Is this possibly because I need to update my unit/navionics card?

You get one year of free unlimited updates from the date of purchase. After that, you need to renew the card. You can purchase the renewal on the Navionics website. As far as periodic updates, I usually update mine every couple of months, or whenever I go to a new lake I haven't been to before.

Your Nav. card doesn't tell you at what pool your lake is at today. The card was made at full pool. I always check the lake level of the lake that I am fishing. If the lake is 10 ft. low; the shoreline is at the 10 ft. contour. If you are fishing a hump showing on the map to have 20 ft. of water on top; your depth finder will read 10 ft. on top when you arrive at the hump.

There is no card that changes the depth of the contour lines with the rise and fall of lake levels. I find this very simple to live with; because I use the contour lines to locate irregular features and adjust my findings depending on the lake level. As above; if I was looking for irregular features to fish in 20 ft. of water, I would be using the 30 ft. contour lines to do that search. When I get to the lake with WayPoints already in place on the 30 ft. contour map, we will be fishing in 20 ft. of water out and around those features on the 30 ft. contour line.

I've wondered about this.

Are we saying they survey a lake's bathymetry (depth) whenever they can regardless of pool level and then adjust their contour data for full pool before making their map cards?

Can't imagine they only schedule a lake's bathymetry (depth) survey when they know it's at full pool. if thats the case then they'd never survey some lakes that seem to rarely be at full pool for any length of time.

They do exactly what you are talking about on some lakes. You can tell that the shallow water coves have been adjusted. One of there worst jobs was done on Toledo Bend as far as the computer Nav. Apps. goes. Many of the deep water coves just stop giving contours and goes to a BLUE map. It is those lakes that have been adjusted that the Lake Master card is much better. Lake Master seems to have these allowances figured out better than Nav.. I have even noticed that the Hard Drive on the depth finder being much more accurate than the Nav. Card; but not often.

It's too bad the LakeMaster cards don't run in Lowrance. But I believe that LakeMaster is owned by the same parent corporation as Hummingbird so they're joined at the hip and not likely to make their cards compatible with Lowrance, etc. Too bad - they're likely leaving money on the table by not supporting anything other than Hummingbird.