We also did the "BOB" excursion in ST. Thomas last year and I'd say go for it,
it was so different and neat. You will have one diver for every 2 bobs, so if
you are having difficulties, they are there to help you, take pics of you,
point things out and lead the way, you go on a trail...

The actual time you have on Bob is about 20 minutes, you can snorkel either
before or after your turn or just stay on the boat.

Have fun!

Donna
Tuesday Chat Host
http://www.cruisemates.com