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Underwater Scuba Accessible Only Cache


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^_^ My friend and I are planning to do an underwater scuba accessible only cache. Since the terrain will be at least a 5 and who knows about the difficulty, we want to stock the cache with some great items to find / trade.


This cache will be a saltwater / underwater cache located in So. California’s Pacific Ocean.


We need ideas for the contents of the cache as well as ways to tether items to the cache so they don’t float away. Since this cache will be underwater and continuously exposed to the elements were are looking for items that meet the following characteristics:


Will not cause any harm to marine life

Will not endanger a swimmer / diver

Will withstand the exposure to water for a long period of time

Must not be corrosive

Should be neutral and or negatively buoyant (should not float)

Should not contain any sharp edges (necessary to retrieve and put into a BCD or goody bag with out damage of puncture or tear.)

Should not be larger than a brick.

Should weigh < 3lbs



Any recommendations / suggestions are greatly appreciated.



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I often leave matchsafes in caches (they make good micros - they also make good matchsafes). If you opened them so that they filled with water they would be fairly neutral, and meet all your other requirements. They cost about $1, so they're not exactly primo swag, but they're okay swag. Geocoins at about $6 (USA and other) would also meet your requirements and definitely be great items to find. Though I'm not sure about the metals and salt water immersion.

Edited by Isonzo Karst
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I don't live anywhere NEAR the coast, (actually, either one..) but I feel the need to point out a couple of things:

First and foremost, seawater is very corrosive. Yeah, yeah - I'm not telling you anything you don't know already. But you're talking about tethering things to the cache. Which means to me; that they're not going to be IN the cache, so they would be out in the corrosive element, so to speak. Is that a good idea? Is that really what you have in mind?

If so, then I will step off and let you go with it.

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Very true Charlie, but if someone filled a cache with them, could you behave yourself, or would it be like Lays potato chips (you wouldn't take just one)?


Obviously, items that are less susceptable to corrosion would be high on the list, but if the cache could be reliably made watertight, then other items could be included ...

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If the cache is watertight, then it has to be brought to the surface to open. Then it needs to be in shallow (less than 30ft) of water, or the diver's dive profile gets real funky. Down, up, down up. A good way to get bent. From the OPs question, he's thinking access the cache at the bottom (or at the cache level underwater) which is the right way for diver safety. Obviously gold coins are the perfect solution. :unsure:

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:D We have started to build the cache container.


This is 4” ABS with an end cap on one side and a threaded end cap on the other. The tube is approx. 12” long with about 5”s of concrete in the caped end. The threaded cap is tethered to the main tube with 60lb fishing line and a swivel to allow the cap to rotate freely. There is also a shackle ring mounted to the end cap which will be used for tethering to a concrete block. Once all the concrete is dried I’ll get some pictures posted.


The cache will not be water tight and accessible only underwater. This is for the safety of the divers so they don’t have a bounce profile and end up getting bent. The depth should be between 35 & 45ft. :D


:D We plan on using a diving float and lift bag to get the cache down to its new home. We estimate the concrete block we are making will weigh between 50-60lbs with an eyelet on the end of the block. :D


:D If anyone is willing to donate some gold coins I’ll make sure that they get placed in the cache. :D


So far some of the ideas for the contents of the cache are the following:


Gold Coins :D


Gold jewelry

Plastic gift cards

Plastic Calling cards

Travel Bugs (not sure how corrosive they are)

GeoCoins (not sure how corrosive they are)

Diving related gear (Dive lights, glow sticks, air cards, oring kits, etc)


We are still working out the logistics for the various waypoints to the cache and the heading’s required for underwater navigation using only a compass. For those divers out there do you trust your kick cycle estimates in order to determine distance underwater or do you prefer the line / grid approach?

Edited by Cabellero42
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Here are some ideas for the diving related gear / swag, what do you think?


Diving Related Gear:

Air Cards

Abalone bar

Aluminum Lobster Gauge

Key chain scuba tank

Mini Scuba Tank o-ring kit

Soft Brass o-ring tools

Tank Valve Covers DIN / Yoke

BCD Fin holder

Hose clips

Hose protectors

Tank Bangers

Goody bag / mesh drawstring bags

Mini dry box

Fish ID card

Underwater notebook


Mask strap cover

Swivel / carabineer

MISC BCD clips / accessories


Mask straps

Fin straps

Snorkel keeper

Chem sticks / lights

Weight belt clips

Ankle weights

Soft belt / BCD weights

Tank Pressure Checker



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