Anything wrong with a 100 WR watch?

I'm a watch lover myself and I'd like to take my dive watches with me when I go into the water. Watch manufacturers typically say that a 100m water resistant watch is not suitable for scuba diving, and there have been arguments about how moving a watch underwater will increase the pressure, hence the rating for WR is not applicable as the test was done when the watch sits still.

Here's what I don't understand. The dynamic pressure caused by you moving your arm is only a tiny portion of the total pressure. For every 4.5 m/s of velocity, that is equivalent to 1m of water pressure. I'm not sure how fast you guys swing your arms, but for me, dynamic pressure is certainly not a big component is the total pressure that the watch experiences.

So my question is, for a recreational diver who does not plan to go deeper than 40m, is a 100m WR watch adequate? Am I missing something here?

I have read reports elsewhere of people taking 100m watches diving without problems.

Personally, I wouldn't. The only dive watch I have is a "proper" one, a Citizen Aquamount which is 200m rated and is actually useful underwater because it records dive information as a basic backup to my computer.

Just taking a potentially expensive watch diving for pose value has no meaning and you might be unlucky.

Purists would argue that any "dive watch" that is only 100m rated is not actually a diver's watch in the first place.

I used to dive with my Timex Ironman and Atlantis (rated to 100m) down to 30+m regularly with no problems. I don't press any buttons though until the shallows where I use it to time my stops.

100M WR rating basically means you can swim in a pool without worry. Going on a scuba dive, it's a crap shoot whether or not it will survive. Dont bump it, dont touch the buttons if you are diving with this.

Casio warranty says for scuba use the watch should be rated for 200M WR or more.

For scuba use, I've always been told that you need to purchase a product that is rated to at least 3X the depth you plan to dive (not just watches.)

the_explorer:

Here's what I don't understand. The dynamic pressure caused by you moving your arm is only a tiny portion of the total pressure. For every 4.5 m/s of velocity, that is equivalent to 1m of water pressure. I'm not sure how fast you guys swing your arms, but for me, dynamic pressure is certainly not a big component is the total pressure that the watch experiences.

Click to expand...

So you take a long stride. Let's make this easy and say you have the watch on your fin and the drop is about 1m. In reality the watch would be higher up (and so moving faster by the time it reached the surface) but water drag starts slowing you at some point too.

The watch is going to smack the surface at about 4.5 m/s. What is the impulse pressure at that point? In other words, the pressure when a watch that was traveling 4.5 m/s through air strikes water that is moving 0 m/s. I honestly don't know. I suspect it is more than 0.1 bar for that instant of impact. The water must accelerate to move out of the way, and water isn't especially light. It could reasonably be 10 bar for a few milliseconds.

Where are you getting your movement = pressure calcs? THEM is probably correct that momentary impulses can be MUCH higher. All it takes is that micro-second of pressure to breach the seal. Once the seal is compromised, it's going to flood, even at mild depths.