Search patterns... help!

[Zept]

The story so far: I'm doing the PADI Rescue Diver course. Took us three searches to find our missing diver (actually a pair of fins) on the first day. By the third search we were thoroughly frustrated and our instructor was practically saying, "I put them there. Go and fetch them."

Our main problem is finding a way to keep our expanding square the right shape when there is a slight current. Vis at the site is poor (1-2m) and the bottom is silt with the odd rock or feathery hydroid, so it's difficult to tell whether we are drifting. So...

1) Any tips for detecting currents?

2) What's the best way to compensate for the current?

We are running the square with one person navigating and the other (on the outside) looking for the fins. We ought to be able to find them... we are not completely incompetent... but so far it seems to be 90% per cent chance, 10% per cent skill.

Any advice would be much appreciated!


Zept

 

[SDAnderson]

The real world intrudes yet again, or maybe there's a lesson here...

Why would you use a square pattern in low vis with a current? That would seem to be a huge PITA. It would seem that an expanding circle or sweep pattern would be easier to control and more effective.

Steven

 

[Zept]

We tried a circle the next day with no more success. It was easier to control but we couldn't cover as much ground -- with only one person on the search track, rather than two, we were only expanding about 1m per circuit.

In a real-life situation, based on my experiences so far, I would go for the circle -- less speed, but more certainty. However I would still like to master the damn square! I expect I'll have to get it right to finish the course. Also, in real life I don't carry a reel, so it would be good to have more confidence in my squares.

Zept

 

[Jonathan]

I'm with reefraf - definitely sounds like a job for the expanding circle. Even using the square you are only going to be going 1-2 m at a time.

My first search on rescue diver ended when the "bodies" got so cold they came and found us! But it was 2m viz and they had buried themselves in a trench!!

Second attempt was a laugh - we were by a container (Wraysbury) and my buddy decided to ignore my briefing and stayed anchored on one corner of the container, which I found out when I swam into the container..... Ouch!

 

[ikan bilis]

did a search and recovery during my advanced course using squares and circles...couldn't find anything.

turn out that the instructor didn't throw in the stuff he wants us to find...you can imagine what happened to him post course.:mean:

in poor vis, i think i will go for circle, at least the reel will guide me back to my buddy.

 

[Butch103]

Even though it was/is tedious, the expanding circle is the only way to go in low vis situations bar none...............

 

[Rick Murchison]

With a soft bottom that's markable, dragging a knife tip to mark the square is quite effective, and serves the dual purpose of ensuring you don't expand beyond your visibility each time around. If searching in zero vis, a line is required, and a handler is optimal. In the real world we'd use a harness and, if at all possible, surface supplied air.
Rick

 

[SDAnderson]

Rick Murchison once bubbled...
With a soft bottom that's markable, dragging a knife tip to mark the square is quite effective

Wouldn't you be concerned that currents or a change in visibility would cause big problems with this?

Steven

 

[devilfish]

reefraff once bubbled...
It would seem that an expanding circle or sweep pattern would be easier to control and more effective.

Steven

Whatever pattern circle or sweep, never do search while expanding, sends diver away from "home" then when low on air, any emegency they have to swim. Always start the far distance estimated or agreed upon and always to the search pattern while "coming home".

 

[Rick Murchison]

reefraff once bubbled...


Wouldn't you be concerned that currents or a change in visibility would cause big problems with this?

Steven

No.
Doing it right you're never out of sight of your marked track - and having the marked track to use is a hedge against currents in an expanding square search, for the same reason.
The key is "markable bottom" - too soft or too hard won't work, and the expanding square in a current without some way to mark your pattern is a bad idea. (you can use markers stuck in the bottom, too, sometimes... depends on the bottom composition, vis, etc)
Again, in the real world, doing a real recovery, the pattern used will be dictated by the conditions, we'd use a harness and line, tenders, and if at all possible, surface supplied air.
Rick