Just out of interest I ran it through my Navionics App... Caye Caulker to Laughing Bird Caye is 85 Nautical Miles and at a sailing speed of 6.5 knots would take 13.5 hours each way non-stop. By powerboat running at 30 knots it would be 3 hours each way but you would have no internal organs by the time you were done.

Google Earth is a very handy tool that will allow you to see most of the waters of Belize and also by using the measuring tool you can estimate distances.

Trips to the atolls are very expensive if it's just for a swim due to the high cost of fuel.

If you want to do day trips from Caye Caulker I suggest contacting Raggamuffin Tours.