How do you determine Visability?

[WaScubaDude]

Aside from WAG (wild ass guess) do you know good ways to determine accurate vis?

[mwhities]

I give my buddy the end of my line on my 100ft spool and have hime swim till I can't see him anymore. I have it marked every ten feet. If it's more than 100ft, I say the viz was 100ft+.

[SkuaSeptember]

1. count kick cycles to the furthest object I can see clearly
2. look up at dive flag or boat periodically and check depth.
If either of these two methods are applicable, the viz is great!
3. Can I see the full body length of my buddy? If yes, vis is ok
4. If #3 is no - can I see my fins? If yes, vis is marginal
5. If #4 is no - can I see my hands at arms length? If yes, vis is poor.
6. If #5 is no - can I at least see my gauges when held close? If yes, its a braille dive, but WTH I'm already wet, maybe it'll get better.
7. If #6 is no - probably gonna call the dive.

[rox@ucf11]

I just guesstimate

[cmburch]

As a building contractor and taking part in other recreational activities, I'm pretty good at estimating distance. I make a comparison to commonly known distances. So I also guesstimate. For example, 6' person, 8&10' sections of wood or multiples of, 25' car, 25yd pool or firing range, 50m pool, 50-75yd range, 100yd field, 1/4 mile track, etc. Also shorter lengths such as inch, centimeter, millimeter, foot, 2 foot, yard can be estimated similarly by comparison.

Visibility for me is the distance that I can I still make my buddy out - that I can recognize that he/she is actually my buddy (not a nondescript diver) or the distance that I can recognize whatever I am hunting.

[Dive-aholic]

Like cmburch, I'm pretty good at estimating distances by comparing known objects. My usual reference is body length of a 6' tall person.

As for what determines distance for me, if I can still see a hand signal, then that's the distance of the visibility. Once I can no longer be sure what hand signal I'm looking at, then we're out of the operational distance even though I may still be able to see the diver signaling me because at that point I'm can't respond and am no help to that diver.

[CaptainRon]

I just rate visibility in my log as good, fair, or poor. What I rate good in a local lake would be poor in the Cozumel so my method is all relative.

[cummings66]

I don't guess at it, I'll say how many feet I had because I don't believe relative is what I want to know 10 years from now. I'd like to be able to know that the new construction they did dropped vis 5 feet for example.

So, I use common things like the height of a person, or I find an object under water I am heading towards and count my kicks to get there. That tells me how far it is.

I don't use vertical measurements because they're often wrong, vis is measured horizontally. There is no guessing involved, for me at any rate.

[CompuDude]

I estimate the distance I can make out distinct objects.

[WaScubaDude]

Originally Posted by Dive-aholic

snip....
As for what determines distance for me, if I can still see a hand signal, then that's the distance of the visibility. Once I can no longer be sure what hand signal I'm looking at, then we're out of the operational distance even though I may still be able to see the diver signaling me because at that point I'm can't respond and am no help to that diver.

This sounds great and I think should be the standard for what constitutes visability, then just have to answer the distance question.

Haven't worked out an underwater system, but in the NW forests there is some rule of thumb, seriously, You hold your thumb out at arms length, close one eye and a tree the size of your thumb is something like 1/2 mile away.

Maybe measure the distance away a 6ft upright diver would be the same height as your outheld thumb, or frammed in the thumb and finger "L". Just have to let your buddy know you don't really mean to signal him that he is a "L"ooser.