Where to book Grand Cayman semi sub?

I am trying to find something for my family of six (with four children ages 2 - 12) to do in Grand Cayman. In my research there seems to be a Seaworld Explorer semi sub ( not the 100 ft one but the semi one) but I can't seem to find an official website for it. Has anyone done this? How did you book it? How close was it to the cruise port(s)? Thanks in advance for your help.

You can book it through the cruise line or even after you get to the port independently.

We booked this right at the dock upon arrival. It's just down the street to the right as you leave the dock area. We did one late morning and there were only a half dozen people on it. It was great as you could move from one side to the other. When we got off there was a huge crowd waiting. It was a very nice time and not too expensive as I recall.

Thanks for the replies everyone.