Estimating Current

[tursiops]

Tides can be predicted over 100 years in advance.

True for astronomical tides. In those areas where other things (western boundary currents, topographic changes, eddies, strong winds, waves, etc) influence the tides, particular the currents, things are not nearly so nice. I'm using "tides" in the common, generic sense of water moving up-and-down and sideways, on a daily or half-daily basis...not the more technically accurate meaning of astronomical forcing only.

I certainly agree that the tables are only a rough guide....

 

[Mikkelse]

I previously found this article on the topic interesting/informative.

 

[tursiops]

I previously found this article on the topic interesting/informative.

Nice link!
FYI, USN SEALS abort a mission if the sustained currents are greater than 1.5 knots. if that is a strong current for them, is is WAY strong for me!

 

[Silty Sam]

Southpoint Divers, a Key West dive op that has taken me to the Vandenberg several times often posts the on-site current in their daily dive reports. I will ask them how they do that, and report back...

 

[Silty Sam]

Southpoint Divers, a Key West dive op that has taken me to the Vandenberg several times often posts the on-site current in their daily dive reports. I will ask them how they do that, and report back...

Here's some insight from Southpoint Divers in Key West:

"Usually it is a guesstimate made while setting our line system by one of our instructors or dive masters who is out there every day and pretty experienced. We usually call the dive around what we estimate to be 3 knots or so, depending on the level of experience and comfort of most of our divers. We hang a spare air reg to about 15ft on a heavily weighted line and if it is pulled more than 40 degrees or so from vertical we will usually call it without even getting in."

 

[tursiops]

Here's some insight from Southpoint Divers in Key West:

"Usually it is a guesstimate made while setting our line system by one of our instructors or dive masters who is out there every day and pretty experienced. We usually call the dive around what we estimate to be 3 knots or so, depending on the level of experience and comfort of most of our divers. We hang a spare air reg to about 15ft on a heavily weighted line and if it is pulled more than 40 degrees or so from vertical we will usually call it without even getting in."

That's nonsense. 3 knots would exert maybe 200+ pounds force on a scuba diver trying to hang onto a mooring line. No way.
I simply would not trust their current "guesstimates" nor their supposed safety procedures.
It would probably take a 200 pound weight on the spare air to hold it to 40 degs in a 3 knot current.
With the more likely 20 pound weight, a 40 deg tilt would likely be achieved with only a 1 knot current, which is MUCH more likely.
And at just 1 knot, the poor scuba diver hanging on the line would only have a 20-25 pound drag on them. Doable.
So they should stick with their hanging-rig tilt as a measurement, and totally throw out the "currents" they think they are seeing.

 

[Scraps]

You need some sort of fixed object to judge current by eye. Most people over-estimate current when guessing it based on feel.

At the bottom, time how long it takes you to drift 5 yards. Pick an object five yards downstream of you. Most people can eyeball a reasonable approximation of the distance of a free throw. If you drift over that object in less than 5 seconds, you have an unswimmable, irresistible 2 knot current but you were too busy getting swept along to time it anyway . . . 9 seconds is a strong 1 knot current . . . 18 seconds is about a half knot . . . 36 seconds is about a quarter knot.

The only number you need to remember is it takes 9 seconds to drift 15 feet at one knot. You can do the math from there in your head for slower currents.

 

[Nemrod]

I have also dived the Vandenberg with Southpoint as my booking store. Nice people, clean boat, no problems. There was a rooster tail coming off of the buoys and it was drug nearly under but we dove.* The next year there was no current at all.

*That was the trip that three dufuses laughed at me and my suggestion that they tether their (3) GoPros and selfie sticks. The sort who use a word that starts with "f" as an adjective, noun and adverb as well as verb. I soloed with my camera/strobe rig but went in with it cross strapped. So I could use my hands on the down line. They lost all three GoPros with sticks and only I and one other fellow made it down to the wreck for a dive. Not sure if the current was above the Seal Team limit but I felt it was at least moderate or so, lol.

N