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How to hide an underwater cache?


Darren V
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Something that is usually designed to hold water?

Not necessarily true. Something designed to hold water in, is not always designed to keep water out -- the opposite is also true. There is a pressure factor many don't think about. 10 ft. under water is far different pressure than 6" under water.

 

Ammo cans work reasonably well. You really ought to test it to the depth you need. Weight it down deeper than what you need it for, and leave it for a week to a month. Do multiple types of containers at the same time and eliminate "work".

 

EDIT: Then pray that somebody doesn't compromise the seal. A seasoned diver probably would not.

Edited by Gitchee-Gummee
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I suppose it depends on the depth. Among plastic boxes Otter Box is a better brand than Lock N Lock. We have one to protect expensive electronics in water situations. I don't know to what depth an Otter Box can be safely submerged.

 

Otter boxes are not waterproof for long immersion. They have a gore-tex hole in them for pressure equalization. It will let water vapor in, which will then condense until the pressure is equalized, which means that the box will fill with water over a period of a few weeks.

 

Ammo cans can be waterproof. For my underwater cache I use a polycarbonate water bottle suspended upside-down, which eventually fills about half full with water. Use waterproof inkjet paper for the log and all is well.

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I've heard of another variation of the upside-down bottle design suggested by fizzymagic, although it's more expensive and more work. Basically, it's a length of PVC pipe with a cap at one end and a ball valve at the other end. The cache is anchored so the end with the ball valve is pointed down, and the end with the cap is pointed up. Even if the ball valve fails (unlikely) or is closed improperly (more likely), air pressure will keep the container from filling completely. If the PVC pipe is large enough, then you can stick a smaller waterproof container (e.g., a match holder or Bison tube) inside it, for a "belt and suspenders" solution.

 

I've also found a submerged ammo can that was dry inside. The big weakness is if someone traps a plastic bag between the gasket and the sealing edge when they close it. The plastic will wick water into the container. (The same goes for many other waterproof containers, of course.)

 

And a weakness of all submerged containers is when seekers get moisture in them when they open them. It's hard to remove the human element from the game...

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I did an underwater cache in one of these. Unfortunately it got stolen before it it even got published. Before I put it out I submerged it in a bucket of water for a week and it never leaked a drop. You can get them at Wal-mart in the camping section.

 

drybox.jpg

 

testing it in a bucket of water its only good if you are going to hide at shallow depths

 

as you go deeper you need to take into consideration and account for the pressure changes

 

this is a container we found 20' down

 

8dab88f3-9f6e-4009-9ef6-d152ffb81e4b.jpg

Edited by t4e
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I did an underwater cache in one of these. Unfortunately it got stolen before it it even got published. Before I put it out I submerged it in a bucket of water for a week and it never leaked a drop. You can get them at Wal-mart in the camping section.

 

drybox.jpg

They have smaller ones now that will hold most cell phones, so they are big enough for SWAG. I have a under water cache that I use the w/p match boxes, they keep logs dry.

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If you're targeting scuba divers, depending on what the location is like and how deep the cache is, the usual recommendation is to design the container to deliberately allow water to enter and pass through it. That's because divers will be tempted to open the cache under water and so will do it at some point. It also eliminates any problems coming from pressure differences, but also means you have to think of something special for a log.

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I did an underwater cache in one of these.drybox.jpg

My wife saw those and bought me one, thinking since it said "Waterproof" it must be a good container. I tossed in a couple odds and ends and threw it in the bed of my Toyota. After a couple weeks of bouncing around with all the other detritus back there, it had standing water in it. I couldn't find any breach points, and the seal appeared OK. Not sure where the water came from. I just know I won't be using one of those as a cache container.

 

The submerged cache I hid was an extra thick baggie, in a Lock & Lock, in an ammo can, affixed to a weight. It passed the two week swimming pool test with flying colors, but failed the human test. The way it was set up, seekers were supposed to snag the cache and haul the whole works up out of the water from the security of their kayaks. Someone unhooked the can from the rope and dropped it. It got lost in the weed covered bottom. He brought me back my ammo can.

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My wife saw those and bought me one, thinking since it said "Waterproof" it must be a good container. I tossed in a couple odds and ends and threw it in the bed of my Toyota. After a couple weeks of bouncing around with all the other detritus back there, it had standing water in it. I couldn't find any breach points, and the seal appeared OK. Not sure where the water came from. I just know I won't be using one of those as a cache container.

 

 

i can only speculate that it was from moisture built up inside the container due to temperature differences

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What type of container would be best to use for an underwater snorkel/scuba cache?

We have one in our area thats about 20ft down in a river. Its an ammo box with a thermos inside and a matchsafe inside the thermos and its full of rocks for weight. Its been there a month and we visited it again yesterday and everything inside is dry as a bone. The can looks rough on the outside but perfectly dry on the inside.

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i can only speculate that it was from moisture built up inside the container due to temperature differences

In Florida, that's a very distinct possibility. Condensation does weird things down here. I expected to find a few drops, maybe. What surprised me was the volume, (enough to fill a film can), and the lack of apparent entry point. My best guess was that something heavy had rolled up against it and temporarily deformed the lid, allowing a gap to form, but there are no stress lines suggesting that. :unsure:

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If you're targeting scuba divers, depending on what the location is like and how deep the cache is, the usual recommendation is to design the container to deliberately allow water to enter and pass through it. That's because divers will be tempted to open the cache under water and so will do it at some point. It also eliminates any problems coming from pressure differences, but also means you have to think of something special for a log.

 

Actually scuba divers invented this great thing back about 100 years ago called a slate. This works rather well when it is used with something called a grease pencil.

 

Here is a link showing how to make your own divers slate. It also lists variations of pencil ideas that will work and even includes a way of securing these items together. (so they dont float away)

 

http://www.scuba-diving-smiles.com/dive-slate.html

 

I believe that something along the lines of a pelican case will be MORE than sufficient for the depths associated with recreational diving. The benefits of the pelican style cases in that they have bleeder valves on them to equalize the pressure.

 

If you are going to place something underwater it has to be able to handle the pressure at depth (2 atmospheres at 33ft, 3 at 66ft etc...) and also must be negatively buoyant. Ensure that the weights are properly secured to the case. If not all divers know how expensive lead can be and might be tempted to abscond with it...

 

Hope this helps.

Edited by devildoc5
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If you're targeting scuba divers, depending on what the location is like and how deep the cache is, the usual recommendation is to design the container to deliberately allow water to enter and pass through it. That's because divers will be tempted to open the cache under water and so will do it at some point. It also eliminates any problems coming from pressure differences, but also means you have to think of something special for a log.

 

Actually scuba divers invented this great thing back about 100 years ago called a slate. This works rather well when it is used with something called a grease pencil.

 

Yup, that would be one of the options, and is what the most well known local scuba cache uses. What I haven't figured out about that combination yet is how durable the actual writing is, and how the pencil itself would hold up under water.

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