It's worth skipping Palm and heading on south for another hour or so and visiting Petite Martinique or PSV. The snorkeling SW of PSV is decent. There's a small cut through the reef on the south side of PSV where you can get the dingy through. I'm sure I've got the coordinates somewhere.

And.... of course the snorkeling SW of Mopion is stellar.

If you can find a good place to anchor the yacht near Mopion, I'd love to get the coordinates! We took the dingy from PSV to Mopion.