Depending on the port, they usually run every few minutes. We've never had to wait more than about 15 minutes to get on a tender. In some locations, due to the size of the tender, you might wait on it for a bit for it to fill up, but it's reasonably quick.
Typically they run in a rotation to and from the ship all day and there's usually more than one so when one is at the ship, one is at the port and then they pass each other shuttling to and fro. What you DO need to be very careful of is the last tender that leaves the port. It will leave prior to the all aboard time so check very carefully when you head off the ship and make sure you are there at least 15 minutes prior to the last one.
They are small boats so you are going to feel the rocking more. I continue taking Bonine every day when we are on the cruise. You are going to have movement when the ship pulls out of port and it's better to have it in your system to prevent any problems.
Dumb question --- can you get seasick on the tender boat (like, while waiting)? I don't usually take Bonine on port days, but I might if the answer is yes.
I once got pretty seasick waiting for other passengers to load on to the Alilaguna in Venice...but that boat is pretty small.
Thanks.
I did not have ANY problems while on the ship, at all. I took Bonine starting the night before the cruise. I was pretty good on the tender boat TO Grand Cayman, but for some reason (perhaps it was all the Rum Cake at the Tortuga Rum Store???) I was sick as a dog.