You can't upload on mine either. You still have to enter stuff manually when you get back to the boat.
This is supposed to be possible using a "user chip", but I know Mike Garside has been round this loop a few times with the manufacturers, but still cant get it to work yet.
Meanwhile, however, I get great fun out of doing all my route planning at home on the PC.
for some detailed examples of my handywork.
As you can see this sort of thing is particularly useful if you wish to share routing information with others.