I have a Humminbird 858c HD Di and just purchased a marine XL Navionics Platinum chip. I should receive it in a couple days. I'm going to an area that I fish 70% of the times but it hasn't been contoured yet. I want to get sonar recordings for this area because I'll be fishing it for 5 days starting April 7th. Can someone give me an idea about how long I can record and save to the card without uploading to Navionics. I don't know where I can get a WiFi connection to log on and upload. Also, can I record, save the data and continue to record the following day. Thanks for any and all help.

Record on a separate SD card. You can use up to a 32 GB card.
The size of your recordings depends on how long you are willing to wait for the upload to the Navionics server with the connection you have.

When you get the card, do an update so you will have current data and you will see how long that takes. That will help you consider how long you want to deal with a upload.

You can stop and start recordings as often as you want.
Each recording is a separate file.
Each recording is given a waypoint name with a "R" prefix. That indicates the location of the start of the recording.

I record in about 30 minute segments.

OK, thanks Wayne for your reply. I know it takes a lot of time to download to update a chip. I'll get a 32GB SD card and that should be enough to last me until I get home and can upload. Appreciate it!!

At what boat speed do you use to record for sonar charts you want to upload to Navionics?

You record at any speed you want. The depth and location data is what Navionics uses.
To get the highest definition data, you want the track points close together, so idle speed is best.
If you run 70 MPH, your track points will the far apart.
The data you provide is only as good as you choose to make it.

When I record, I go as slow as my boat will go-I want the highest detail contour lines.
When I am recording in timber/stumps, I use the trolling motor SLOWLY.
Additionally if you want your HD lines accurate, you need to do your tracks close together-unlike what the mapping companies do which creates errors between actual recorded locations.
That is the dreaded "Interpolation" that they don't admit they do, but is a physical fact.

You can do a less detailed recording, upload your data, download the Sonar Charts and rescan any errors you want corrected.
The accuracy of that program will be as good as those contributing.

That makes a lot of sense. Thanks Wayne for the reply.