The Holiday is a Dolphin Watch ship with multiple trips daily (including the daily sunset cruise and Fireworks Cruise on Tuesday evenings in the summer during Harbourfest). The Holiday is located right in Shelter Cove Harbour right across from the
DVC Resort and is only a short walk. The 2015 prices are not yet out but it was $16 for adults and $8 for children during the season. -
http://www.hiltonheadisland.com/adventure/ In the photo on the web site, the DVC Resort is the land on the right side of the photo of the boat. The Holiday is a fairly large ship, so the encounter is not as up-close as the smaller boats but you will see a lot of Dolphin during the cruise and Captain Mark does a great job narrating the cruise. The cruise is about 90 minutes in duration.
There is also the Crabber J - which offers crabbing trips daily (in season). Our grandkids have gone on this several times and have a lot of fun. It is a catch-and-release program and the child who catches the most gets a Crabber T-Shirt.
We are also local to HH and I am looking out the window at the Holiday (and the DVC Resort) as I type this!