Teva's are the one's I found on the internet. The pair I found are called Teva Neutron Advanced Watersocks. They cost 39.99. The description says "non-marking Spider Rubber outsole for grip on both wet and dry surfaces". So it sounds like they would work nicely for the sailboat too. I think I'll try them.
For Dunn's River Falls, I too used an old pair of sneakers. But my feet got very sore walking around after the climb because the shoes were still wet so I'm looking for something that will dry quicker.