Speed of current

[CaptSaaz]

I've been on a few dives where there has been current. I mean more than drift dive current in Cozumel... Current as in, deflate you BCD so you hug the bottom to give you a chance to hold on to something and not get swept out to sea or pushed to the surface uncontrollably type of current.

Question is... how do you measure current? Is there a device to measure the speed of the current like an anemometer for wind speed that you can carry down?

 

[Thalassamania]

A knot is 1.68781 feet per second. That's about 4 seconds to travel the distance from your head to the end of your fins if you're moving at one knot.

 

[Doc]

Good advice above.

Yes, there is such a device, but it requires you to have it anchored (as a reference point). I have no idea what the US Navy paid for them, but it had to be insane.

You could easily jury rig a simple version with any hinged pointer airpseed gauge, like the kind that are on back yard rain gauges. Test it, measure it and move it underwater in a swimming pool. Calibrate it like that.

In Tobago, we actually laser measured a chute called "The African Express Turnoff" and then timed it. I recall it was approx 4.5mph and we tumbled thru it.

 

[Bobbin-along]

We teach students the following:

6 feet in 10 seconds is 1 knot.

Which is offically Thass' definition of a knot but in easy to see terms. THis is useful for measuring current before you get in, and if you are stationary in the water and a piece of kelp goes by and you time it floating from head to foot, or head to fin depending on your actual height.

 

[sschlesi]

According to Thalassamania's numbers it's about 6' in 3.5s or almost 17' in 10s. 6' in 10s is well under half a knot.

 

[Thalassamania]

According to Thalassamania's numbers it's about 6' in 3.5s or almost 17' in 10s. 6' in 10s is well under half a knot.

T'aint my numbers, came from Rubber Bible I keep on my desk. I can't hardly remember PI to that many digits, that why I use ²²/₇.

 

[nereas]

I've been on a few dives where there has been current. I mean more than drift dive current in Cozumel... Current as in, deflate you BCD so you hug the bottom to give you a chance to hold on to something and not get swept out to sea or pushed to the surface uncontrollably type of current.

Question is... how do you measure current? Is there a device to measure the speed of the current like an anemometer for wind speed that you can carry down?

Please apply to the DDs forum as an honorary guest. They are also into such gadgetry. Although knowing their RMV does not interest them much, knowing how fast they are being swept along by the current is right up their alley, as it were.

 

[nereas]

We teach students the following:

6 feet in 10 seconds is 1 knot.

Which is offically Thass' definition of a knot but in easy to see terms. THis is useful for measuring current before you get in, and if you are stationary in the water and a piece of kelp goes by and you time it floating from head to foot, or head to fin depending on your actual height.

1 kt = 6076.1155 ft/hour

which equals 6076.1155 ft / 3600 seconds

which equals 1.6878 feet per second

which equals 16.878 feet per 10 seconds

I believe you are off, at least according to the math.

 

[Thalassamania]

You mean like this:

Test diver Riza Lacour burns up the speed course, measuring a fin's top speed with a digital underwater speedometer.

 

[nereas]

T'aint my numbers, came from Rubber Bible I keep on my desk. I can't hardly remember PI to that many digits, that why I use ²²/₇.

With a moniker like THALASSAMANIA

I therefore trust that is a Greek Orthodox New Testament Bible,

and preferably in Greek?