Do I need to purchase a ferry ticket in advance?

Hi
Planning to take the following ferries: Stockholm-Aland, Aland-Helsinki and Helsinki-Tallin. I saw quite a number of posts say that its cheaper to buy the ferry ticket at the last minute. My question is, because I'll be traveling in August, is there any possibility that the ferries will be full (I don't plan on getting a cabin.) Also, some of the companies say there is a surcharge if you do this. It would stink to have to waste a day if the ferries were full.

Thanks in advance
srbsep

I can't answer that for sure, but I would warn you that it may make a difference whether you travel Thurs-Sun or Mon-Wed. Because the boats are much fuller on the weekends. Also, I think it's less likely that they'll run out of passenger-only tickets, if any are overnight boats , because when I was on the boat last month, there was only one other non-cabin passenger. (Beware, it's not comfortable. We curled up in opposite corners in the hallway, and people came and looked at us with varying degrees of pity and curiousity . . . )

isnt it cheaper to book a few days in advance (or earlier!)?

Before mid-june and most of august and later on the ferries will not be that busy, except some weekends. The peak season is in July, maybe the first week of Aug, but July is usually more busy here.