Visibility

[MaxBottomtime]

I usually estimate using body lengths. With fins, most divers are about six feet long. I don't count shadowy figures as visibility. If I can clearly make out what a shape is then I count that distance. On one amazing shore dive I actually measures lengths in the sand using my fin tips. We had 40 feet vis and it was the best I've ever seen on a shore dive in SoCal. When I read reports of 50-60' vis around here I just shake my head.

 

[Agility]

logged a fair few terribles during our most recent trip, which was to Fuerteventura

Oh, I did not know visibility was an issue around the Canary Islands, I hope it will be better when I get there in two weeks :blessing:

 

[DeeperOut]

When diving in challenging visibility environments, I use a marker buoy or an anchor line for descent. I have set up different color markings for 1 meter and 5 meter increments, or just tie knots in the marker buoy. Although visibility differs vertically and horizontally due to sediment distribution, this is a rough reference that I find useful. If I am not in need of reliable measurement, body length is a basic reference.

Agility - dived Tenerife in August , visibility was routinely 20-30 meters, 10 to 7 on choppy sea days. Depends on the weather you get and how well the guides pick the sites due to conditions.

 

[emoreira]

Visibility can be measured formally with what is known as a Secchi disk, which is a disc divided into black and white sections. Viz is defined as how far away you can distinguish the two areas from one another,

Secchi disk - Wikipedia, the free encyclopedia

Adding to what TSandM wrote, the method defined by Secchi was for vertical visibility or transparency, and the values measured are referred as Secchi depths. In our case of divers we usually mean horizontal visibility which is worst of what could be measured with the Secchi method, as vertical transparency in influenced by light absorption with depth. The Secchi disk could also be used to measure horizontal visibility with two divers or attaching the disk to a fixed point underwater and measuring the horizontal distance with a reel. This is normally too much for a dive. Considering that in sea diving places visibility can vary a lot from one day to another, doing this is useless. In quarries or lakes, visibility also changes but in longer periods, so, it could be assessed a fresh water dive spot visibility with this method as part of the dive spot advertising.

 

[Pane]

Oh, I did not know visibility was an issue around the Canary Islands, I hope it will be better when I get there in two weeks :blessing:

It varied a lot by weather and currents. But we had pretty lively seas most of the time.

apart from the sometimes murky and choppy conditions, we had some pretty cool dives. We didn't see a lot of colorful stuff, but numerous large stingrays, butterfly rays and several angelsharks.

 

[DA Aquamaster]

Another thing to consider is that the vertical visibility can be greater than or less than the horizontal visibility, and the visibility can change in different layers, especially above, below or in the mixing layer of thermoclines.

 

[Wookie]

The rule of thumb I've always heard and taught is that horizontal visibility (which is all that counts) is about twice vertical visibility. If I can see the bottom clearly in 100 feet, I can count on 50 feet of vis. Obviously, this has to do with ambient light, and assumes that the vis is the same throughout the water column, which is not always the case. Back when I cared about such things, I'd spend at least part of my dive doing kick cycles to figure out how far away things were, as measured by my kick cycles. Now, if I can't see the bottom from the boat, I don't bother getting in.

 

[fire_diver]

Most people just guess what the vis is, and most guess wrong. Compounding the problem is the threshhold people set. What one diver calls 10 foot another will call 20, on the same dive.

 

[Hostage]

Well thank you on the feed back, it answered my question!