We did Trunk bay on our own, and no vests were required. Don't know about the ship excursion, but I don't see how they could make you wear one when most other people are not. Besides, the high salt content of the water makes it really hard to sink. I had a hard time diving down to get pictures, and I'm pretty skinny. The vests are a real pain as they interfere with your snorkel, but a good idea to wear if you are not a good swimmer. We found that a pair of Speedo goggles (just cover your eyes) made for a much more pleasant snorkeling experience. The view was clearer, and they were more comfortable. Of course, you have to be comfortable with having your nose out in the water rather than inside a mask. Even my 8 year old daughter finally gave up the snorkel and mask and just went with the goggles. I would always recommend wearing swim fins as they keep you from getting tired and enable you to overcome most currents, not that we ever encountered any type of current problems.