I've been on two boat trips on the intercoastal waterway. One was a dinner cruise and the other was a couple hour party from a trade show I was attending. Both times, the boat left from the dock across the street from the Diplomat Hotel. There's several boat trips you can take from there.
I was hoping we'd go out into the ocean, but we only went down the Intercoastal waterway. It was lovely tho, but I don't have any good pictures of the views because they were evening trips and everything came out too dark. There are huge lovely homes and mansions along the water as you go south toward Miami. The sunset was outstanding.