Hi Keith, welcome to Cruise-Chat!
As Dave noted, you can't ever be certain of the pier locations. Have you checked out Carnival's diving excursions that are available? They will be more expensive, but they will include the transportation. They will also make sure you make it on the excursion by allowing you to be the first ones off the ship if tendering for early excursions. The ship will also wait for late arrivals if you take the afternoon excursion if available.