Visability -- Measurement

[Sam Miller III]

12 hours and no interest -- post deleted

SDM

 

[Lopez116]

Interesting. I've always kinda wondered that myself. I usually check Laguna Sea Sports' website and deduct a bit off their estimate as I'm sure they have a vested interest in reporting good viz


Sent from my iPhone using Tapatalk 2

 

[Sam Miller III]

Now you know....

Look forward to accurate reports from our water soaked barrister "The viability was 17-1/2 feet vertically and 22-3/4 feet horizontally" or reports of that nature

SDM

 

[Bob DBF]

Up here in NorCal we just look down and check if we can see our fins.



Bob

 

[Sam Miller III]

To Bob DFB
Who does not log dives and wears an old fashioned double hose regulator....

It is reported that if you see a gloved hand in front of your face you bite the glove --If the biting creates pain then the hand is yours if no pain it is your buddies....

And always remember in that horrible low visibility NorCal water bubbles should rise to the surface


SDM

 

[Divebum Don]

Sam, we've had this discussion at many de-briefings. It seemed that regardless of the actual Vizz, many folks can't seem to tell 5 feet from 15 feet with a tape measure. Did a test one time with many divers asking them to guess the diameter of a pipe lying near by (it was 12 feet around). Variation was in the answers was astounding, from 5 to 20 feet. Secchi dish is best.

 

[j2s]

some times I take a small carpenter's ruler (the ones that slide out ) w/me on a dive when I know the viz is low, but don't tell any one. I slide it out and when the end disappears that's the 'VIZ'........Then I ask the other divers what they thought the 'VIZ' was........Calibrated eyes humans do not have !!!!!!

 

[Divebum Don]

Reposted without permission from thread originator, Dr. SDM

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

"I estimate the visibility was 20 feet...." I have heard words to that effect for more years than I care to remember

I have discovered that more often than not the estimate of visibility can be off by a huge factor both plus and minus.

To accurately measure visibility a SECCHI DISK is the answer

In the past (since 1865) the SECCHI DISK was used to measure clarity and visibility underwater.

I still have mine from when I was instructing the Advanced Diving program at Orange Coast College in Coast a Mesa, California-- a long time ago......I taught at OCC for 14 years and only the ADP -LA Co, NAUI and PADI in its infancy. I presented my my last ADP there in 1984..

I made mine from 2 inch round disc of aluminum, with a 1/8 inch hole drilled through the middle, half of each of one side painted black the other side one half painted white. The disks are secured at 5 foot (or predetermined) increments to a length of line, about 30 feet long or longer if needed--in today's water probably considerably shorter.

Drop it into the water and where it disappears is the vertical visibility.
Hold or secure underwater to a fixed object and swim horizontally until it can no longer be seen is the horizontal visibility.

When finished roll it up and stick in the BC pocket along with the rest of the many tools of a recreational diver

No stinken batteries, no stinken computers, no stinken digital guages, no stinken print outs, just a length of string some black & white disks and the Mark One Human Eye Ball. And an accurate measurement of visibility can be made rather than estimated .

I might suggest that you might want to visit and chat with John Rice at the HB Sports chalet -- he was one of my stucents so many years ago and may still have his Secchi disk kit.

FYI from google:
The Secchi disk originated with Fr. Pietro Angelo Secchi, an astrophysicist, who was requested to measure transparency in the Mediterranean Sea by Commander Cialdi, head of the Papal Navy. Secchi was the scientific advisor to the Pope. Secchi used some white disks to measure the clarity of water in the Mediterranean in April of l865. Various sizes of disks have been used since that time, but the most frequently used disk is an 8 inch diameter metal disk painted in alternate black and white quadrants."

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


j2s, I'm a carpenter and tradesman, "Guess'timating is second nature for me, the pipe I mentioned was 50' long, the same Q was asked of the divers as to the length of the pipe?? between 12' and 70' was the variation, we had fun!
P.S. The tube section referred to was one of the new sections installed at the new Terranea Resort while under construction.

Don

 

[MaxBottomtime]

Most divers with fins on are about six feet long underwater. Unless the vis is measured in inches I usually estimate it in body lengths. I have around 400 dives at Marineland and have seen some incredible vis in blue water on a handful of occasions. The best I have ever seen there (I began diving there after Marineland closed in 1987) was a little over thirty feet. That was an incredible dive. Visibility at Marineland is usually five to fifteen feet, with fifteen feet being great vis. I have read reports from other divers saying they had fifty feet or more. I think some feel if they can see a dark outline or shadow in the distance then that is the visibility. I only count what I can clearly make out.

I made a dive at Shaw's Cove in surge and less than six feet vis one day. There was no way anyone could see more than a single body length. A guy on another board who was in the crevice at the same time argued that it was easily forty feet.

 

[keithbt]

Reposted without permission from thread originator, Dr. SDM

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

"I estimate the visibility was 20 feet...." I have heard words to that effect for more years than I care to remember

I have discovered that more often than not the estimate of visibility can be off by a huge factor both plus and minus.

To accurately measure visibility a SECCHI DISK is the answer

In the past (since 1865) the SECCHI DISK was used to measure clarity and visibility underwater.

I still have mine from when I was instructing the Advanced Diving program at Orange Coast College in Coast a Mesa, California-- a long time ago......I taught at OCC for 14 years and only the ADP -LA Co, NAUI and PADI in its infancy. I presented my my last ADP there in 1984..

I made mine from 2 inch round disc of aluminum, with a 1/8 inch hole drilled through the middle, half of each of one side painted black the other side one half painted white. The disks are secured at 5 foot (or predetermined) increments to a length of line, about 30 feet long or longer if needed--in today's water probably considerably shorter.

Drop it into the water and where it disappears is the vertical visibility.
Hold or secure underwater to a fixed object and swim horizontally until it can no longer be seen is the horizontal visibility.

When finished roll it up and stick in the BC pocket along with the rest of the many tools of a recreational diver

No stinken batteries, no stinken computers, no stinken digital guages, no stinken print outs, just a length of string some black & white disks and the Mark One Human Eye Ball. And an accurate measurement of visibility can be made rather than estimated .

I might suggest that you might want to visit and chat with John Rice at the HB Sports chalet -- he was one of my stucents so many years ago and may still have his Secchi disk kit.

FYI from google:
The Secchi disk originated with Fr. Pietro Angelo Secchi, an astrophysicist, who was requested to measure transparency in the Mediterranean Sea by Commander Cialdi, head of the Papal Navy. Secchi was the scientific advisor to the Pope. Secchi used some white disks to measure the clarity of water in the Mediterranean in April of l865. Various sizes of disks have been used since that time, but the most frequently used disk is an 8 inch diameter metal disk painted in alternate black and white quadrants."

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


j2s, I'm a carpenter and tradesman, "Guess'timating is second nature for me, the pipe I mentioned was 50' long, the same Q was asked of the divers as to the length of the pipe?? between 12' and 70' was the variation, we had fun!
P.S. The tube section referred to was one of the new sections installed at the new Terranea Resort while under construction.

Don

I would like to understand how use use 2 inch disc when the secchi disc is 8"...If we go on a dive and I use an 8" disc to measure vis and you use a 2" disc to measure vis then we will not come out with the same visibility numbers....The bigger the object the farther away I can see it....by the way I know John...I stopped going there because of short fills...I'll still go if I need to fill late night (6pm-9pm) though.