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Posted by Rp @ Tz on September 12, 2000 at
13:00:35:
Posted from Host: c360878-a.marin1.sfba.home.com (24.20.188.103)
.Greetings,
We had an interesting discussion yesterday on the forum that I think deserves another round...and maybe a permanent place on the classics..
I started off the thread with a question about who really wears their non-divers watches rated to 30meteres in water...
please add your input..
Robert Burns asked this question:
Posted by Robert Burns on September 11, 2000 at 16:39:57:
:
: So do you (Rp) think that you can swim with today's 30 m....Rated watches? I thought
that it was just light "splashing" and washing your hands? How about the poster
that said he went Diving all the time,with his Zenith! That one kills me! Salt water,and
depths to 25 meters,with a Zenith!
Bob
_______________________________________
My response:
: Hi Bob,
: You can definitely swim in any watch rated for 30 meters....I’m assuming you mean on the surface of the water...but even if you dive you can’t get to 30 meters without an air supply, and most people who scuba or tank dive don’t go much below 100 feet which is the equivalent of 30 meters.....and the watch is safe to this depth
: The cases are designed to take the pressure........assuming the gaskets are in place..
: hope this helps..
__________________________________-
Steven Walker questioned my response as innacurrate:
Posted by StevenWalker on September 11, 2000 at 18:24:43:
: RP, I thought I'd never say it, but I think you're mistaken.
The WR ratings refer to static pressure, under lab conditions, not real life. The
following info is from the Seiko website, but is pretty much standard for all
manufacturers. I personally would not swim with any watch rated under 100 Meters
: Water-resistant to 30 meters (100 feet) - Will withstand splashes ofwater or rain but
should not be worn while swimming or diving.
: Water-tested to 50 meters (165 feet) - Suitable for showering or swimming in shallow
water
Water-tested to 100 meters- (330 feet) - Suitable for swimming and snorkeling. Water-tested to 150 meters (500 feet) Suitable for snorkeling.
Water-tested to 200 meters (660 feet).- Suitable for skin diving.
Diver's 150 meters (500 feet)- Meets ISO standards and is suitable for scuba diving.
Diver's 200 meters (660 feet) -Meets ISO standards and is suitable for scuba diving.
: :::::but even if you dive you can’t get to 30 meters without an air supply, and most people who scuba or tank dive don’t go much below 100 feet which is the equivalent of 30 meters.....and the watch is safe to this depth
____________________________________________\
Then B Hannigan added this:
Posted by B Hannigan on September 12, 2000 at 08:47:14:
...We've had a heated discussion over in Breitling forum. on this very topic of dynamic
vs. static pressure and I think the differences are WAY overblown. Any arm movement, water
current, shower head, water jet, or dive from a diving board, etc. simply cannot not add
much INCREMENTAL dynamic pressure ABOVE what a watch is already experiencing at even ONE
atmosphere of static pressure, or about 10 meters depth. If a watch is TRULY a 30 meter
watch, and properly assembled, then nothing you encounter while swimming or free diving
(from a board) should effect it (disregarding possible shock damage). My explanation is as
follows...
: Consider that pressure at sea level (or the weight of one atmosphere) is equal to about 15 lbs/square inch (i.e. a vacuum will raise a 1 square inch column of water about 33 ft. at sea level, and this column weighs about 15 lbs.). Furthermore, this weight increases linearly as we descend down into the sea., i.e. pressure 66 feet down is equal to twice that of sea level, or two atmospheres. Furthermore, consider that Bernoulli’s law tells us that total pressure at any liquid depth is equal to static pressure + dynamic pressure. Given that we already know what static pressure is at any depth, we then need only concern ourselves with dynamic pressure – How much more would we ADD, by anything we might do or encounter, above what we already expect? That is, if a watch is rated for 10 atmospheres, what might be the maximum pressure that that watch might ever encounter, due to other conditions or circumstances, at any lesser depth? What might this be, as a maximum? As a generous estimate (interpolating from various on-line sources), I would say that no person could generate a velocity of greater than 50 feet/second (or 34 mph), either INTO or UNDER water, and survive. This is approximately the terminal velocity of a free dive into a pool from 150 feet (for reference, a sky diver generates a terminal velocity of only about 170 feet/second, or about 120 mph). That is, nothing you yourself could do, and no condition you could ever survive, would generate a momentary or continuous water velocity greater than 50 feet/second. So, 50 ft/sec = 600 inches/second. Therefore, any movement into or under water at any velocity up to 600 inches/second, would load 600 cubic inches of water onto every square inch of watch surface area, or .3472 cubic feet (i.e. 600 / (12*12*12)). At 62.427 lbs./cubic foot of water, this yields a pressure of 21.67 lbs./square inch, or about 1.44 atmospheres (21.67 / 15 lbs. per atmosphere) maximum momentary dynamic pressure. Note that this is a VERY generous maximum, and I stand by my assertion that no one is likely to EVER encounter or generate an INCREMENTAL pressure greater than 1 ADDITIONAL atmosphere above what the watch wearer is already experiencing in any given condition. Again, unless the watch is improperly assembled or specified, a true 10 atmosphere watch would NEVER experience a momentary pressure greater than 10+1.44 = 11.44 atmospheres at any depth UP TO 10 atmospheres. So, for a 30 meter watch, rated to 3 atmospheres, if you are able to free dive to 33 feet (and generate one atmosphere static pressure), you have my immense respect because your are in world class condition. Add 1.44 possible dynamic pressure and you're still below the 3 atmosphere total loading capacity of the watch. RIGHT?