Sorry to go all the way back to this old post, but thought people might be interested to know that St Helena now has a wharf that, if needed, can be used by cruise tenders to provide shelter. It's in Rupert's Valley, the industrial port in the next valley to Jamestown, so not the nicest way to 'arrive' - but it's now much more likely that you'll get ashore and be able to go on your tours at least.