We booked this Beagle Channel boat ride because of the time of the sailing 1500. It turns out the time given for this sailing is not correct. The ship sails at 1530 not 1500 has advertised.
The ticket sent via email had no location information. I had to get in touch with Ripio Turismo. It is not easy, we had to find café with wifi to email.
The only location information given was Touristic Pier" and go to Rumbo Sur Office" at 1430. The pier in Ushuaia has many booths and many people walking about. As a non-Spanish speaking person it was very difficult to find the proper booth. Two local people nicely took the time to help us. We then found out that all sailings are at 1530.
I believe you would be better off just contacting any one of these booths to do your booking or there was a place on the main street in Ushuaia. Or your hotel! The sailing it self was fine.