Estimating Current

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TMHeimer

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I have thrown a stick in the water, but of course that is only the current on the surface.
 

Silty Sam

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I have thrown a stick in the water, but of course that is only the current on the surface.

Right. We can measure boat speed with the GPS, but that is surface current PLUS wind, depending on what is going where.
 

NAM001

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Anyone have suggestions for estimating or measuring current on a dive?

1KT IS 6000 FT PER HOUR OR 100 FT PER MINUTE. ROUGHLY 1.5 FOOT PER SECOND. PICK UP SOME SILT DROP IT ANS LOOK AT T TRAIL AND NOTE THE TIME. OR IF DRIFTING WATCH HOW FAST LANDSCAPE IS GOING BY AND GUESS THE DISTANCE IN FEET THEN PER SECOND DIVIDE IT BY 1.5 ADN YOU HAVE IT. THERE IS ALSO A MARINER 3 MINUTE RULE YOU CAN EMPLOY ALSO WHICH IS I BELIEVE SPEED TIMES 100 YARDS IS THE DISTANCE YOU GO IN 3 MINUTES. 1 KT = 100 YRDS = 300 FT MOVEMENT N 3 MINUTES OR SIMPLER 100 FT PER MINUTE

sorry for the caps
 

nolatom

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All good (and also funny) answers above.
Here's an old thread about how fast the average diver goes while finning comfortably/uncomfortably/maxed-out:
Average Speed for a Scuba Diver
It seems we amble along "averaging" about half a knot, and "fin purposely" to make one knot. This is a gross generalization and fitness/streamlining vary a lot. As a weekend duffer, I would find a half- knot current to be a lot, and at one knot I'd wonder why they let us jump in unless it was a drift dive, as I would struggle to just stay even with the boat, absent any handholds or wreck-type shelter.

"100 feet per minute is one knot" is the basic thing for a non-metric English major like me.. Then as Turisops and KWS point out, you can break that down into smaller pieces. Let's say most of us are 5-6 feet (or about 2 meters) "tall", as a rough measuring stick. 100 feet per minute is one knot, so in one second you'd make 1.66 feet, and in three seconds about 5 feet. So one of my lengths in only 3 seconds while passing a reference point, that's about one knot, aack why am I here. In 6 seconds, that's better, about half a knot. Ten seconds, that's about a quarter-knot, noticeable but okay. No, I'll never win a math prize but it's doofus simple for me.

Or, when in any doubt, always head up-current from the anchor line to begin with. If you get tired doing that, then be grateful you're not downcurrent.
 

tomfcrist

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Underwater, I classify current in the following categories: none, slight, swimable and hell no.

On the surface I use my GPS to calculate 1 minute drift as shown above...but I use a coconut as the marker. Drop the coconut and a GPS mark on the site. Drive boat to the coconut after a minute and see how far away you are from the drop point....100 ft per Kt of surface current.
 
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