Excellent idea Geoff
I'd suggest the TomTom *.asc format might be a good choice, as well as the *.gpx format used by MemoryMap amongst others.
There are a number of converters to switch between formats available here:
GPSBabel works converting your Garmin file:
It appears to retain the link to the boatlaunch website after conversion to GPX in MemoryMap, but comes up with an error when it tries to load the boatlaunch webpage (I can PM you the webpage error message if you wish).
Converting to the format for my car satnav gives some garbage '"' strings in the data strings but other than that works fine. When I have 5 minutes I'll probably go back to basics and manually convert the Excel file into a CSV to get it all looking pretty - I can send you a copy if you wish.