Updating navionics cards
Historically, there have been some special adapters for for "C-Card" to CF, SD to CF, and other variants.
If you can avoid an adapter in conjunction with a chart plotter it is generally a good thing -- one less possible point of failure.
Now, recognise that a Navionics Gold chart covers a greater area than a single Admiralty Chart Pack and suddenly, in comparison, it doesn't sound quite so bad.
At the end of the day a Navionics "upgrade" is really a new set of charts.
So, if you want to be sure your charts are bang up to date, at some point you have to bite the bullet and go out and buy new.
Older chart plotters, up to about 2013, sometimes used Compact Flash (CF) media cards.
Other chart plotters us either a SD card or a micro SD card that may plug into a "sleeve" with SD card dimensions.
And now that you can download updates from the net and update the charts yourself from a PC its going to get even cheaper. When I bought a new Navionics chart it didn't show the causeway to Eriskay, or the bridge to Scalpay, both of which had been in existence for about ten years, at the time.
As a bonus, it showed an island in Loch Scavaig which doesn't exist, so I suppose I got something for nothing.
All the Navionics cards currently for sale are micro SD / SD media (most commonly) and in CF card media (for the older plotters).