Team member tow boarding in approximately 30 meters (100 feet) of water. During tow boarding, two snorkelers are typically towed behind the vessel in clear waters where the bottom is visible. If they see something of interest, they let go of the tow board, and the vessel returns to the location for a closer look and possible dive. Tow boarding is very effective in clear water where coral growth is extensive. Archaeologists look for straight lines and shapes that do not look like natural objects.