When navigating in areas with uncharted coral reefs it is a good idea to wait until the sun is high and behind you – from 10AM to 4PM. (This is why charter companies encourage you to anchor no later than 4PM.) Height above deck is an advantage to the spotter and vision can be improved with polarized sunglasses. Calm, grey days are the most difficult when trying to look deep into the water. As a rule of thumb in reading the water:
- Dark blue tones mean deep water, 20 fathoms or more.
- The blue becomes lighter with decreasing depth, and the turquoise (green-blue) is a warning of shoaling. it is the color of the coral sand covering a flat expanse of reef with 4-6 feet of water coverage.
- Dark brown indicates coral heads.
- Brown or yellow indicates reefs with a depth of 3 or 4 feet over them.
- Green-brown means a grassy bottom.
- White means very shallow water.