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Good containers for hydrocaches


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That thread plus another similar one were what prompted my brain to travel down this road. While both have some good information, there are not a lot of specifics as to what works and what doesn't. Dry boxes tend to be one the expensive side compared to other cache containers and I'd rather not try to reinvent the wheel if there is knowledge already available.

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I've owned a number of underwater hides. I no longer bother with trying to sink a dry container. My most recent is an old burnt ammo can. I drilled additional holes so it would drain freely and added a divers slate for the log. A person could gaff it from a boat and stay dry, but so far, all finders have waded for it.

 

I've used battery canisters that were originally designed to hold large batteries for underwater filming. These are great for the purpose, but pricey.

If the interior is going to remain dry, cachers will have to take them to the surface, get dry, dry their hands thoroughly to open and close them, and then return them to their underwater location. Experience is that this is not actually going to happen.....

 

I've seen matchsafes inside ammo cans, tethered to the bottom. These were intended to be retrieved from a boat. Seems to work okay, but is actually less foolproof than the same ammo can with holes in it, and divers slate. An air-filled container wants to float, fights the tether, and people can lose control of it while handling. They have fight the buoyancy to reattach as well.

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I've seen, for micros, bison tubes and the soda preforms. Mostly in shallow water where you can reach them from a kayak. The larger swimming key/wallet holders do not stay dry.

 

The largest fully underwater cache I found was a 6" PVC pipe with a screw end fitting and a tool attached to open it. The tool also acted as a weight to hold it down. It was also tied to underwater roots or something with a rope (thin chain?) that reached the surface.

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The o rings on bison tubes will rot if they are in direct sunlight. The best ones have an inner clear container which often stays dry. For larger containers the best is to use 2 containers, such as a lock n lock inside of an ammo can, although the seal on the ammo can will leak after a few years. It will also rust in a salt water environment, even if its not in the water.

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I don't own a hydrocache, but the ones I've seen that have worked well have used a container-within-a-container approach, or have used underwater objects (not containers) bearing the coordinates to a container located safely on dry land.

 

Ammo cans work underwater if the gasket is in good shape and if no one traps anything (e.g., a plastic bag) between the lid/gasket and the rim of the can. Or put another waterproof container in it, and you should be okay unless someone gets water in it when they open/reseal the container (as Isonzo Karst described).

 

Good micro-size containers work when placed within a larger container. Some kayak caches I've done have used PVC pipe with a cleanout plug at one end. The small waterproof cache container is protected from physical damage by the outer PVC container. The log is protected by the small waterproof cache container (unless the kayakers have wet hands, etc.). One downside of this design is that finders sometimes need a wrench to open the outer PVC container, depending on how the previous finder closed it and depending on what exposure to the elements has done since it was last found.

 

One example that I've seen online (but not in person) is a PVC pipe with a ball valve at one end and a cap at the other. It is anchored to float with the cap up and the ball valve down, so even if the ball valve leaks, air pressure should keep water out of the PVC pipe. One downside is that a ball valve large enough for a Bison tube or a match safe or a bottle preform will be rather expensive.

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One design I've seen that actually worked and stayed dry used pvc pipe that had a threaded cap on one end and a glued cap on the other with an smaller watertight container (a bottle blank preform) inside it). It was constructed as follows: the threaded cap was secured to a heavier than water base in about two feet of water with the threads facing up. A foot long 1 1/2 inch pvc pipe was threaded vertically onto this base. The bottle blank was inside the tube with a couple of pieces of the "right sized" foam water pipe insulation as a "plug" below it.

To retrieve the cache you unscrewed it from the base and pulled it straight up. Once you removed the foam insulation, the bottle blank slid out. To replace it: rotate the pipe so that the opening is up, drop in the bottle blank in "cap down", replace the foam plug and then rotate the pipe threads down and screw it back into the base. Water can't enter the vertical tube because of air pressure while it's being screwed in (the foam plug doesn't have to be water tight, just snug enough to keep the bottle blank inside) and once it's threaded the whole thing is water tight.

You can easily imagine variations on the design where the entire assembly could be lifted and opened on land or in a boat...A watertight base connection is not crucial as it's the air pressure inside the tube that keeps out the water.

edexter

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I recently did maintenance on an underwater cache I placed two years ago. (PVC pipe, one end cap glued, the other threaded, with a preform bottle blank inside it) Cache was bobbing on the surface tied to a tree branch by a previous finder who reported the underwater restraint has broken. The cache spend at least part of the last winter frozen in ice. The "waterproof log" inside was still dry. This is a good design.

edexter

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