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Old 06 November 2013, 11:52   #11
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Also worth considering what other options divers have to take down with them ?

Ie what depth can you take a pyro flare to ( without it being in some from of cannister) ?

My ( limited) understanding is that if you're at 50+m you really do need to know what your doing.......

If this guy was 'found' with a laser that didn't exhibit the same optics/ line of light/ safety the greatland flares are designed to emit then it can only be a plus for the greatland ones.
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Old 06 November 2013, 12:20   #12
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Many items specify depth 'tested' in still water. When moving around, the pressure will be higher.

I was once told that a 35m dive (which I only did once for PADI assessment) needed equipment rated at 200m and that a watch rated for 50m when diving would have leaked long before 50m was reached.
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Old 06 November 2013, 13:03   #13
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I have one of Scots (SPR) green lasers, nice bit of kit it is too, I can't see it being a big problem to knock up a watertight (200m) canister. The laser is tiny so a canister wouldn't add much bulk or weight. Might be a marketing opportunity there Scot
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Old 06 November 2013, 13:27   #14
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There are canisters on the market that hold a PLB. I think that there's one for the double ended flare too. I think if I was diving, I'd like to have the Greatland in mine above either of the others...
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Old 06 November 2013, 13:31   #15
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Pressure doesn't change when you're moving about. I'll see if I can remember boules law. At 30m the water pressure is 4 time greater than on the service.
We all live for the most part at 1 bar which is 14.8 psi at 30 m it's close to 60 psi. No amount of moving about will change that
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Old 06 November 2013, 13:43   #16
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Sorry it's boyles law. Something to do with partial pressure of gases under pressure and it's different for different gases but that's another lesson
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Old 06 November 2013, 13:54   #17
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Quote:
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Sorry it's boyles law. Something to do with partial pressure of gases under pressure and it's different for different gases but that's another lesson
You're sort of right. The problem arises when, for example you jump off a boat into the water, if the bit of kit that's rated to "x" meters hits the water first, it could be subject to pressures far higher than the static water pressure. A bit like doing a belly flop. Similarly if it gets a knock or a bang whilst underwater, the shock could be greater than its rating.
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Old 06 November 2013, 14:15   #18
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The engineer in me said "static pressure stays constant, but total pressure increases with the square of speed. I wonder what difference it makes..."

At 30m down, at 2mph: 0.2%.
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Old 06 November 2013, 14:29   #19
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You might have to factor in that things are lighter in salt water or is this getting a bit silly and off thread, LOL
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Old 06 November 2013, 19:39   #20
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Pressure doesn't change when you're moving about. I'll see if I can remember boules law. At 30m the water pressure is 4 time greater than on the service.
We all live for the most part at 1 bar which is 14.8 psi at 30 m it's close to 60 psi. No amount of moving about will change that
Actually, it does. When you swing your arm underwater, you encounter resistance. That resistance is an increase in pressure against your arm. The seal in the watch or flashlight or canister experiences the same thing.

jky

Oh, and as an aside, a green laser can be a pretty good surface marker without actually shining it on an aircraft. Swung around in a circle, it would make a pretty obvious focal point for the pilot to home in on.
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