If you're a member of CAT, there is a video seminar on how to store/save/etc. I teach to save by lake. I am familiar with Lowrance, but I would think HB has something similar.
When deleting waypoints (after saving), the waypoints/trails/routes remain in memory. If you truly want to get rid of them, they must be PURGED! In other words, if you delete 1k wpts, reload for next lake, save, delete, reload for another lake, save, delete... the wpts are still in memory. If both reloads had a 1k wpts, there are 3k of wpts stored in memory. 1k deleted, 1k reloaded, 1k deleted, 1k currently loaded (3 different lakes). That equals 3k of wpts. It can easily be seen where wpts/trails, etc. will quickly overload memory. I have 1189 wpts just for Fork with 111 trails (that contain many wpts - these count too!).
To avoid this, do as previously mentioned: save by lake or region, delete, then purge. If you don't understand PURGE, then read documentation for 'Purge' in G2 or G3 documentation. It isn't in G1 documentation. The documentation states the reason for keeping deletes is to sync up units. I physically save, update the lake file on the computer, then delete and purge from both units. When I go to a specific lake, the only wpts/routes/trails on the unit are for that lake - optimum performance.
By the way, the HDS PDF documentation can be stored on the SD card and read using your unit. This helps if you're out on the water. You could also access the documentation via phone if air service is available. I prefer to read from the unit for easier eye strain and to not have to worry about air service.
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