Letter Re: The Get-Home Cache, by The Feral Farmer

Hi Hugh –

With respect to the recent article about buried caches, burying an igloo-type cooler sounds like a great way to lose an entire cache of stuff. First, the suggested six inches of soil covering provides nowhere near enough protection from a vehicle over an otherwise unsupported area the size of a cooler lid. With no earth-arching over the flat lid, I suspect (but can’t prove) that it would fail if a heavy vehicle tire went directly over it. Second, and perhaps a more valid concern, is that if placed anywhere other than a hillside with great drainage, it will float out of the ground during heavy rain unless it weighs enough to remain negatively buoyant.

The net buoyancy of an object is equal to the weight of the water its volume displaces minus the object’s weight. Using the cooler linked in the article (a 48-quart Igloo), you can see its dimensions are 26.08in x 14.63in x 14.5in, or roughly 3.2 cubic feet. 3.2 cubic feet of water weighs approximately 200 pounds (varies with temperature). That means such a buried cooler would be positively buoyant (i.e., would want to float) if the cooler and its contents weigh anything less than 200 pounds. Now some amount of positive buoyancy is probably okay, as the weight of the dirt above would help prevent floating to some extent. But keep in mind that we are talking about a rain event and disturbed (previously dug-up) dirt is much more porous than undisturbed dirt and therefore will turn into mud much more readily, and mud isn’t going to provide much protection from floating. For better safety it would be prudent to ensure that the cache is negatively buoyant by doing the math and weighing it or by performing the swimming pool test described in the link below.

This issue was previously mentioned right here on SurvivalBlog – Matt R.

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