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Old 03-29-2013
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Cloud shadow on water vs Rock/coral head in water

they both look dark. When sailing in the shallow water in Caribbean, does anyone know a trick to distinguish these two?

Sometime you can look at the sky for clues. But most of the time is hard, and you only have a minute or so to make the decision even you are standing at the bow.

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Old 03-29-2013
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Re: Cloud shadow on water vs Rock/coral head in water

Polarized sunglasses help. Cloud shadows are much bigger. Try using parallax. Move your head around. The time of day also matters.

Also check your charts for the Co abbreviation.

Navigate Through a Coral Reef Safely--Use These Seven Tips
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Old 03-29-2013
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Re: Cloud shadow on water vs Rock/coral head in water

I go around cloud shadows when I'm not sure it's a cloud shadow. Last time I crossed from Nassua to the northern Exumas (the Devils Back Bone) my track line was rediculous. The light was funky that afternoon and half of what I saw was actually cloud shadows, better safe than on a head I alway's say.
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Old 03-29-2013
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Re: Cloud shadow on water vs Rock/coral head in water

Cloud shadows move and even though you may be moving, the cloud shadows move at a different rate, almost like cross track error. In situations where you can't tell, slow down and the above will become more apparent. Your depth sounder and chart should give you an idea if what you are looking at is even shallow enough to hit and most often it isn't, unless you are where you shouldn't be. I remember places in the Bahamas where it seemed as though we would be aground in seconds, but the water was actually 90 feet deep!
In areas without charts, like the atolls in the SoPac, we only moved during the hours when the sun allowed us to see through the water, sometimes only 4 hours a day, anchoring until the next day.
You'll get the hang of it pretty quickly, once you are doing it daily, but once in a while everyone gets fooled. Carry a good stock of Rolaids.
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Old 03-29-2013
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Re: Cloud shadow on water vs Rock/coral head in water

Cloud shadows move with the the wind, Usually easy to determine which is which is which. Also they are much larger than heads. A cloud would be like a reef and most of those are well charted in the Bahamas.
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Re: Cloud shadow on water vs Rock/coral head in water

Yup. Polarized sunglasses and with the sun at your back.
The higher the glasses and eyeballs are from the deck, the better.

If the least bit unsure, miss them all, including dark grass.
Dont think for one nano-second that charts will always be correct for reefs and coral head in the Bahamas or TCI, etc. ... they do 'grow' and sometimes die off. Even the explorer charts will sometime have it wrong.
Use your eyeballs when on 'thin' water.
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Re: Cloud shadow on water vs Rock/coral head in water

I wonder how many people hit heads that thought they were cloud shadow or dark grass.
I grew up on a sail boat in the Key's. I worked on coral reef research vessel for 4 years, and I own a dive and snorkel boat in Key West as well as a house in the bay Isalnds of Honduras, with a veiw of the reef. I drive a 7 foot draft tug boat back and forth across Biscayne Bay for a living, and bla bla bla, I'd like to think I can read the water pretty good. I still go around dark spots if I'm not sure what it is, and it happens. I've never hit a coral head though.
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Re: Cloud shadow on water vs Rock/coral head in water

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Originally Posted by Capt.aaron View Post
I wonder how many people hit heads that thought they were cloud shadow or dark grass.
I grew up on a sail boat in the Key's. I worked on coral reef research vessel for 4 years, and I own a dive and snorkel boat in Key West as well as a house in the bay Isalnds of Honduras, with a veiw of the reef. I drive a 7 foot draft tug boat back and forth across Biscayne Bay for a living, and bla bla bla, I'd like to think I can read the water pretty good. I still go around dark spots if I'm not sure what it is, and it happens. I've never hit a coral head though.
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Re: Cloud shadow on water vs Rock/coral head in water

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Originally Posted by rockDAWG View Post
they both look dark. When sailing in the shallow water in Caribbean, does anyone know a trick to distinguish these two?
Only "trick" I know of is the same advice given to those who want to know how to make it to Carnegie Hall...

"Practice, practice, practice..." YEARS of it... And even then, as Aaron and others have mentioned, you will not always be absolutely certain at a glance...

If you see any hint of brown in the coloration, trust me, it isn't the shadow of a cloud... (grin)
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Re: Cloud shadow on water vs Rock/coral head in water

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Originally Posted by jackdale View Post
Polarized sunglasses help. Cloud shadows are much bigger. Try using parallax. Move your head around. The time of day also matters.

Also check your charts for the Co abbreviation.

Navigate Through a Coral Reef Safely--Use These Seven Tips
Thanks for the excellent link
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