What is visibility?

[MaxBottomtime]

I always find it funny when someone says they had only 3' visibility. I ask them if they could see their fingers when they stretched out their arm. They're surprised when they realize that the viz was probably quite a bit better than 3'.

Visibility is very subjective with new divers. The estimates are always interesting.

I've had way too many dives when I couldn't see my hands.
We were diving at a local shore site once in pretty poor vis. We could barely see a shadowy figure more than a body length away. I estimated visibility at 4-5 feet that day. A guy who was diving with us said it was 15-20. I don't know what he was smoking.
I have some buddies who are like that. Whenever they tell me what the vis was on their dive I mentally divide it by two.

 

[JohnnyC]

So, the technical way is with a secchi disk as mentioned up thread. A more practical measurement for divers in limited visibility is the distance at which you can resolve your buddies communications.

In gin-clear water in a Mexican cave or in the crack at Silfra the visibility is essentially unlimited.

 

[chillyinCanada]

This is all, of course, assuming 20/20 eyesight.

 

[Bob DBF]

I always find it funny when someone says they had only 3' visibility. I ask them if they could see their fingers when they stretched out their arm. They're surprised when they realize that the viz was probably quite a bit better than 3'.

Or you are, when they say no.


I'm pretty accurate when I can see my fingers it's 3' or so, and if I see my fins its around 5', more viz than that its a lot easier to dive and not run into something. On the NorCal coast 15' or so is the viz I get a lot, once it starts getting 20'+ I enjoy it, but I can't estimate worth a crap.


Bob

 

[JackOfDiamonds]

Personally when I say 10ft of visibility I mean that past 10ft I cant see anything.

If I can see something , even if it looks like a blob, that still counts as having visibility.

 

[TMHeimer]

Personally when I say 10ft of visibility I mean that past 10ft I cant see anything.

If I can see something , even if it looks like a blob, that still counts as having visibility.

Yeah, I'll go with that. When I started out PADI said somewhere it's the distance you can see (make out?) another diver. So that's what I strive for, which is difficult when solo.
As far as predicting viz, I look mostly at waves (talking shore dives obviously). Bigger waves/surge over sandy bottoms can mess things up a lot. Sometimes clearing up at depth, away from the surge. Storms that recently passed through can leave some turbidity behind. Some "inlet" dives have better viz at incoming or high tide since water is coming in from the sea, not going out from bays that rivers enter into.

 

[Scuba Lawyer]

I guess its all subjective as to eyeball unscientific measurements. When I say visibility is 15 feet, I personally mean to convey that I can see things pretty darn well-ish at 15 feet lateral distance but beyond that things are indistinct.

How's that for specificity?

 

[MaxBottomtime]

Same here. I don't count blobs, shadows, visions, etc. If I can see color or clearly make out what I see, I count that as visibility.

 

[Ghost95]

Or you are, when they say no.


I'm pretty accurate when I can see my fingers it's 3' or so, and if I see my fins its around 5', more viz than that its a lot easier to dive and not run into something. On the NorCal coast 15' or so is the viz I get a lot, once it starts getting 20'+ I enjoy it, but I can't estimate worth a crap.


Bob

Very surprised if they say no!

 

[Scuba Lawyer]

On the NorCal coast 15' or so is the viz I get a lot, once it starts getting 20'+ I enjoy it, but I can't estimate worth a crap. Bob

I still remember one day (jeez it was 31 years ago) we had 50' vis at Sea Ranch. I had gotten abs the day before freediving so I took a tank out to go spearfishing the next day. Got the biggest lingcod of my life on that dive. If anyone has ever dove Nor Cal in the Gualala area they know how lousy vis can be. I still talk about how fantastic that dive was.