Dry Box...A Series of Tests

[mccabejc]

Bought a small Otter dry box to keep my keys and stuff in when I go diving. It occurred to me that the box would have some buoyancy when submerged, but I couldn't find any info on how much. Would I need more weight to compensate? Would it screw up my trim?

Well, I decide to perform a series of tests. Filled the sink with water. Put the box in. In spite of the strange looks from my girlfriend, I pressed on. And, in a stroke of genius, I went into the kitchen and grabbed one of those little postal scale looking things that you use to measure the weight of food. I then inverted it, and pressed down on the box floating in the sink until it submerged. Turns out I needed about 5 oz to get it under water.

So, my guess is that in salt water the box represents about 1/2 lb (8 oz) of buoyancy. Not enough to worry about.

To all of you who have been losing sleep worrying about this, go to sleep, and worry no more. This is my gift to you. No extra charge.

 

[MikeC]

Don't you have any small fishing weights or bullets hanging around? What are the dimensions of this box?

 

[mccabejc]

Brilliant idea. Fishing weights. Excellent. Yes, quite excellent.....

Dimensions are 4 3/8" x 2 7/8" x 13/8"

 

[MikeC]

Also what was the cost, rated depth??? Is there a lanyard attached??

 

[nwdiver2]

There are lead weights made for the small digital camera housing that would give you neutral buoyancy. The case is about the size of a small housing. Or use lead weights or shot in a piece of nylon stocking.

 

[Furner]

Wouldnt the contents of the dry box contribute to neutral, or even negative bouyancy?

 

[The Kraken]

Yes, they would.

 

[Furner]

Well then, adding lead to the box seems useless, unless you are planning to dive with an empty dry box, which wouldnt make any sense at all......

 

[mccabejc]

MikeC, the box is about $8 at DiversDirect.com, 100 feet rated, with a big ol' lanyard attached.

As far as contents contributing some negative buoyancy (or "sinkiness" as I like to call it), yes, in some cases. Actually I was planning to stuff a blueberry muffin in it for my breakfast, which, according to my tests, has a net "sinkiness" of approximately -1.2 ounces. In otherwords, it has some "floatiness".

Seriously, a single car key (at least my single car key) is sinky to the tune of less than an ounce. That leaves a net floatiness of the box plus contents of about +0.7 ounces. Hence my trip this evening to Wal Mart on the way home to get about 6 ounces of sinkers.

 

[The Kraken]

If one is trying to determine the amount of buoyancy the empty box would add to one's kit, it would make a great deal of sense to see how much weight would make it neutrally buoyant so that one could add that amount of additional weight to offset the buoyancy of the container. Therefore, adding weights of know amounts would enable the diver to determine, exactly, how much weight s/he would have to add to the weight belt or weight system in use.