We went to Tulum about 10 yrs ago and it was very interesting to see.
The ferry ride was very rocky and I have heard many tales from others about how rough it was for them.
We are former New Yorkers, used to riding the subways. We were the only ones able to stand up, to see the view and take pictures. If you take any meds for seasickness, be sure to take it before the trip to Tulum.
I suggest doing the ships excursion, not going on your own. If you are on your own and get back late, the ship will leave without you. It will not leave until all the ships shore excursions are back.
sue
p.s. I lived in Staten Island for 18 yrs.