Cinque Terre - ferries ever too full that you miss a scheduled time

[Travel To Be Free]

How full are the ferries the first part of September?  Are you able to get the upper outside deck easily?   Do you ever run a danger of missing a certain timed ferry or can you prebook a time?   

[marazul]

Not that full.  Yes, no problem getting the upper deck.  You do not have to prebook a time.  It is like catching a public bus, butyou  do have your round trip tickets so there are no delays buying them.  

The only danger of missing a ferry is if the seas are very rough because they might cancel.  So, play it by ear.  If the seas are rough, go back early, but ask at the ticket office.  They will tell you what they expect.  Your option in case of cancellation is the train.