No, you do mot have to register ahead of time. I believe they rely more upon "walk-ons" as their "office" is between the heavily traveled tourist sidewalk ans the roir boat itself. The "waiting area" is very small and crowded but there are so many things to do and see for the visitors before actual boarding.
I found a fantastic discount on Groupon! I purchased ticket on Groupon from my phone and I was able to download ticket on there :)
Your dont have to but if advise to do it
Not necessarily but recommended so that you can be sure of getting a spot on the boat.
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