I did that Es Vedra trip two years ago (I think) bought tickets and got onboard in front of Mar y Playa in Figueretas.Was told beforehand that the boat would be going via Formentera because of a problem with another boat (or something) fine with me...left about midday,20 euros.
The boat lingered a bit by Atlantis,the sun worship lot were not amused,can't say I blame them,
then slowly circled Es Vedra before heading back,pulled in closish at a couple of bays to have a look but chose Sa Caleta to stop for swimming.People had been fishing all the way but this was where they caught the biggest ones!
On the last stretch back they break out the Cava and are quite generous with it.
Very enjoyable afternoon,usually about 3 hours+ pretty sure it's still available,recommended.