Spot on. MicroSoft Explorer can read the cards, but the operating system is not MicroSoft i.e. not FAT32 or DOS. RayMarine kit will not recognise the card if it is formatted using a MicroSoft operating system. If you can work out what OS they use to format the card, you could copy all their charts free.
B careful eek, Sandisk especially as they usually come with something
Any markings? If not then just maybe personal stuff like camera. More likely something backup - Oct 06 you could buy 2MB cards easy so a 512MB?
For nav/charts they have some very clever low level stuff and tend not to be the latest sizes. It's FAT formatted, but the clever bits are on the MBR and below which makes them a devil to copy
Stingo should be put in a basket or low shelf and retained in a junior compact flash capacity until you need fish or biltong, but you already know that
I'd stick it in your digi cam. I use that size in my Nikon. I don't use larger ones as this size is usually enough for a job and bigger ones always have the risk of a catastrophic loss of data.