Low vis searching in the real world

[Cthippo]

I have a couple of local wrecks I want to do soon in very low vis water (1-2 feet on a good day). Both of them I have dove on this year and not found, despite having good coordination. I understand the theory of doing a circular line search, but how do you do it in the real world?

What are you using for an anchor?

Have you added a ring or other attachment point on the anchor line to keep the search line from getting tangled? How far off the bottom?

Are you knotting your search line to mark off distance? How far between knots?

Does watching your compass to know when you have done a full circle work or is there a better method?

What if the anchor line is not vertical?

Any other clever tips?

 

[happy-diver]

I've got no hope

But I can see

 

[Edward3c]

I have a couple of local wrecks I want to do soon in very low vis water (1-2 feet on a good day). Both of them I have dove on this year and not found, despite having good coordination. I understand the theory of doing a circular line search, but how do you do it in the real world?

What are you using for an anchor?

Have you added a ring or other attachment point on the anchor line to keep the search line from getting tangled? How far off the bottom?

Are you knotting your search line to mark off distance? How far between knots?

Does watching your compass to know when you have done a full circle work or is there a better method?

What if the anchor line is not vertical?

Any other clever tips?

Is a circular search the best for what you’re looking for.
Does The object stick up much from the bottom.
Are you using floating or sinking line.
Answering these and others will help.

My suggestion is you practise on land to see how things work. Working with lines/rope underwater is a recipe for entanglement.

 

[Celt]

Simplest method. Drop a heavy weight in the centre of the search area with a floating rope to the surface buoy. Drop down and attach your line and reel to the weight. Move out that you can see the weight and drive a peg. Swim around the weight till you come back to the peg. Pull the peg and move out the same distance and drive the peg and swim around the weight in the opposite direction till you get back to the peg. Keep the line tight. Repeat.

 

[Jim Lapenta]

If you've dived them, but not found them, how do you know you were actually on them? Seems contradictory.
What type of wrecks are they?
Are they in an area where they can be fished? If so, that opens a whole new can of serious risk.
How deep?
How reliable is the information? It's common for captains to give misleading numbers to protect their honey holes.
Circular searches can be excessively time consuming and inefficient.
Grids or even semi circular can be more effective.
I always tied of to the anchor or near it by putting in a stake and taking a heading. Then sweep in arcs for a set distance or distances. If the object was not found, back to the start point and go off another heading.

 

[Cthippo]

I can say for certain both exist. One is an old fiberglass boat and I got footage of it with an underwater camera from a kayak some years back, so it certainly was there and I doubt has been removed.

The other one I have been running side scan over and am certain has not gone anywhere.

Both are in 15-25 feet of water depending on tides, and with the sonar and some patience I should be able to drop almost on top of them, but when you can be 2 feet from something and still miss it, I need to have a backup plan.

I'm also thinking about the person whose G/F lost their phone in the lake. If I was to take on a task like that, how would I do it?

 

[boulderjohn]

Low visibility searches are pretty tough.

I have done several searches in visibility that poor, and I cannot claim to be proud of the success rate. The first time, we did a circular line search with a guy in the middle turning the line, letting a little more out each time we complete a circle. I said "we" because there were two of us on the line, spaced about 5 feet apart. We found the object of our search when my buddy ran into it--literally bumping it with his forehead without seeing it. I think that if it had been between us, we would have missed it.

Other times I have tried a line search, the line ended up getting entangled on something.

I have done several searches using a compass and kick cycles to cover a grid with mixed success. I have decided you really need two people with a compass--one doing the navigation and one doing the searching.

I met a man who did police searches in poor visibility. In one case, they had two divers on each side of a line, with their hands holding both the line and each other. Suddenly his buddy's hand pulled away, and then he ran head-on into something. He tried to turn, but he was trapped. It turned out he had swum into the back seat of an upside-down car. His buddy had run into the intact front door.

 

[rjack321]

Put the shot line right in the middle of them. There is no need to "search" if you get the shot right.

 

[Celt]

A circular search is very accurate, once the jumps match the viz and you’re certain you’ve covered the area, approximately 30 feet in poor vis. 15 feet of line. To big a sweep gets messy. On the last sweep if the object isn’t found you have to decide what direction you wish to move the weight. Drive the peg on the outside perimeter in the direction you wish to move and tie off the reel. Go back the line, put a bag on the weight and bring it to the peg and start another circle, unfortunately covering ground already searched is unavoidable with a circular search in order not to miss ground.