Timex Ironman Question

[Marek K]

I agree with (most of) the others; the 100M Timex should be fine for what you're going to be doing.

The reason most scuba watches are rated 200M or more is that there can be dynamic pressures in addition to the depth pressure -- like if you hit the watch against something at depth, the additional force might be enough to rupture it. As far as I understand.

And yes, try not to press any of the buttons underwater; the seals around the buttons are almost certainly not designed for that (another reason why these kinds of watches aren't recommended for scuba). They'd probably work anyway, but no certainly.

Um, just in case the watch does crap out on you underwater, it might not be a bad idea to have a back-up timing device with you... like another cheap 100M Timex... otherwise you'd have to abort the dive immediately, and might not be sure how much bottom time you'd had.

--Marek

 

[p1medicshawn]

I own both the Ironman and the G-Shock. I have had both to 150' in the warm Carribean and the COLD Canadian waters. Both have functioned without any problems. I do prefer the G-Shock because of it's lighting and the band seems to be a little larger than the Ironman. Have a great trip and enjoy yourself! Just remember, it's only $35.

 

[CompuDude]

I agree with (most of) the others; the 100M Timex should be fine for what you're going to be doing.

The reason most scuba watches are rated 200M or more is that there can be dynamic pressures in addition to the depth pressure -- like if you hit the watch against something at depth, the additional force might be enough to rupture it. As far as I understand.

You've got the right idea, in general, but it's a smidge off.

The issue at play is indeed static vs. dynamic pressure. When they pressure test watches, it's done under static conditions: They put it in a pressure tank and squeeze until it pops. Under those conditions, the watch is perfectly still in the center of the tank, and pressure is hitting it equally on all sides.

Now go into a pool and put your hand in the water. Feel the pressure? Great. Now move your hand sideways 3 feet, in a normal swimming way. Feel how much more pressure there is on the leading edge? You just multiplied the pressure on that leading edge by well over 4x (I don't have the exact math handy). So merely moving an object in water is going to dramatically increase the pressure it has to deal with, as well as setting up low pressure and higher pressure areas unevenly around the watch. Hitting something is not even required, just moving it around underwater while already at a high pressure level. Suddenly your 60' dive, multiplied by 4 (and it could very well be 10) is exerting 240' of pressure on your watch.

Suddenly 100m doesn't seem to give you very much margin...

 

[WeekendDiver]

I have a $5.95 walmart watch which I use for it's stopwatch function. (timing ascents). it has been on with me on pretty much every dive down to 150ft. the writing on the case is worn off but it stll works just fine. And pushing the buttons U/W is not a problem. Obviously i have a 'puter and a bottom timer also, but they don't show seconds....

 

[Marek K]

You've got the right idea, in general, but it's a smidge off. [...] The issue at play is indeed static vs. dynamic pressure. [...] merely moving an object in water is going to dramatically increase the pressure it has to deal with

Wow... when I'd heard the issue was static vs. dynamic pressure, at first I did assume it was pressure differences while swishing the watch around in the water. But then I thought, nah, the pressure can't be that much higher when moving. And hitting the watch on something is dynamic!

But your explanation makes a lot of sense... when moving the watch in water, you're multiplying (rather than just adding to) what is already high static pressure.

Is the pressure increase factor dependent on depth, or just velocity? Are we really realistically talking about 10x pressure increases with normal motions?

What's the over-engineering factor?

I'm one of those guys who uses a 100M watch (butt-ugly Timex Helix DM). No problems, even with occasionally pressing the buttons underwater. But, again, it's a back-up (with its depth gauge) to my computer.

--Marek

 

[Dixie Sands]

I had an ironman fill with water at 180ft but until that point it had served me well for 3 years.

 

[CompuDude]

The static pressure increases with depth, the dynamic pressure increases with movement. It's possible there is a slight increase in dynamic pressure with depth as well, as the water itself becomes more dense, but that's a far less significant number. I really don't know what the numbers are, but suffice to say I buy a 200m watch. The $10 I save buying 100m vs. 200m is not worth the hassle of a potential dead watch at some point. I don't care about the money, just the hassle!

There is an amount of over-engineering, as witnessed by the number of people who dive with 100m watches all the time. But I'd prefer to spend a few bucks more and not have to wonder if my watch is going to die this dive or it'll make it one more time.

Besides, Costco had 200m Casio G Shocks on sale for $40 a couple years ago, so I'm all set.

 

[Dermochelys]

If I can find an inexpensive 200 meter I'll get it, but for this one week I think I'm going to stick with what I've got. Plus, if it does break I can buy something in Hawaii and I won't be heart broken that I lost $35. Thanks for all the input though, bringing up the static pressure vs. dynamic pressure is a very good point.

 

[Dermochelys]

Ok, here is the report on the Timex Ironman 100 meter. I was only able to do 2 dives with it in Kauai over the past week. The first dive had a max depth of 45 feet and the second only 35 feet. On both dives the watch did just fine, I even pressed the buttons underwater at depth with no ill effects. I'll be in the market for a real dive watch, but for this trip it worked great. For anyone not going deep I would say that this makes for a fine, inexpensive watch. Thanks again to everyone for your input.

 

[Marek K]

The static pressure increases with depth, the dynamic pressure increases with movement. It's possible there is a slight increase in dynamic pressure with depth as well, as the water itself becomes more dense, but that's a far less significant number.

OK, so, the dynamic pressure component is relatively constant, for a given "swish" velocity?

So what is that dynamic pressure, vs. velocity?

Because when I swish my hand through the water, I don't think I'm feeling even 1 ATM's worth of pressure... but then, I'm not sure what 1 ATM of pressure feels like...

--Marek