Yes, you tender in Half Moon Cay, but that is no problem at all. You will love the Island! Beautiful and very relaxing day. Great barbecue lunch! If you have to tender in Key West it is a long ride so be perpared and try and get a tender ticket as early as you can. Key west is a great place also!
We had to tender in KW and it was awful. The ship is a LONG way out. When we were there HAL rented an old fishing boat to take us in as the seas were VERY rough. We were packed in like sardines, 99% of the pax had to stand and you could barely breath much less move. It was extremely dangerous and a big mistake for HAL to do, IMO. It was very dangerous getting on and off the fishing boat. At the time many other Oosterdam pax complained on the boards of what I am saying here.
Only problem with tendering in HMC is that it prevents the ship from going to the island at all on some occasions.
When we cruised there in 2003 I referenced the port authority's website to see exactly where we would be docking. If you are unfamiliar with it, here it is:
Click on the month you are crusing to see details of your day in port. Those marked with (B) or (M) are docked with no tender. I think this is why I used the word "most" when referring to docking based on recollection of charts at the time of our cruise there.
You will see that on days with few ships in port, most are docked (which also depends on if ship is of suitable size). Obviously when supply of docks is less than demand of ships, some get to tender. (We docked at Mallory Square next to another cruiseship)\
Cruised on Maasdam in March 03 - Docked in Key West - we arrived in the late afternoon. However, we never made it to HMC or Grand Cayman because the seas were too rough to tender!