I've been cruising the BVI for years and the only time that I've had mozzies is when the wind dies down completely. With normal trade winds any mosquitoes venturing out to the anchorage just get blown past the boats, their maximum speed is 1.5mph. I have screens aboard, but haven't had to use them. While docked it is a different matter, since that is ashore and usually in protected areas. But not at anchor or on a mooring.