Trisno is right on. The Navionics Update card can be used with your Gold and Hotmap Premium cards. You cannot use the Update card with the Platinum+ card but you can update it online. I believe the cost on that is about $200 USD.

You will need 1 update card per card. Your old cards will still work. You can download anything you like for North America on the Update card and your only limitations are 2GB of data (which will hold Huron, Ontario, and Erie) and a 1 year time frame.

-Lawren