Yes, thank you for your inputs. The ship has excursions that have Tulum and beach stops, so they can do it. They are $150/head. Worldwide, I've usually researched enough to venture on my own and make it back to the ship on time. So with a large group of 8, I am trying to pinch every penny and see it all (culture and beach). You should my med cruise especially my stop in Livorno, Italy (Saw Florence & Pisa all in one day via trains, buses, cabs).

It looks like I will seek to be first off ship. Catch the ferry to Playa del Carmen. Catch the first possible ADO bus to Tulum. Do the Chevy Chase or more at the Temples/Ruins. If really cool, hang out if not go to beach.
What I haven't heard yet is if there is a beach walkable from the ruins?? As always, If public transport fails me, I'll have dough necessary to hail a cab and haul butt back to the ferry dock.

Interested in more inputs...Thanks