16800 bezel rotation

[dskjl]

My 16800 mat dial 7.2 serial number bezel only turns counter clockwise is that normal or is the spring etc... installed incorrectly?

Advise with pics if possible on how to fix it if it is indeed abnormal would be great.

Thanks

[The GMT Master]

Originally Posted by dskjl

My 16800 mat dial 7.2 serial number bezel only turns counter clockwise is that normal or is the spring etc... installed incorrectly?

Advise with pics if possible on how to fix it if it is indeed abnormal would be great.

Thanks

As it's a diving bezel, it's only designed to be turned one way so that it doesn't get knocked underwater. Only the very early Subs had bezels you could turn both ways.

[Balboa]

Originally Posted by dskjl

My 16800 mat dial 7.2 serial number bezel only turns counter clockwise is that normal or is the spring etc... installed incorrectly?

Advise with pics if possible on how to fix it if it is indeed abnormal would be great.

Thanks

It turns only counter clockwise?

[jasonpage]

The idea is that, during a dive, you use the bezel to time your decompression stops as you ascend to the surface.

These stops give the nitrogen that's built up in your body during the dive time to slowly escape from your organs and tissue. If you simply pop up to the surface after a long dive all this nitrogen will be suddenly expelled and you get decompression sickness - aka the bends. It's not pretty! It's like opening a fizzy drink that's been shaken up. Unscrew the top gradually... no problem. Take the top off quickly... very messy.

Well it's the same when you're diving at depth for any length of time... only it's your vital organs. Consequently, it's a good deal messier.

This is why your bezel only turns anti-clockwise - so that if you accidentally nudge it while underwater your decompression stop will get longer (hence safer) rather than shorter (hence more dangerous).

Hope this makes sense.

[dskjl]

Originally Posted by Balboa

It turns only counter clockwise?

yup

[dskjl]

Originally Posted by jasonpage

The idea is that, during a dive, you use the bezel to time your decompression stops as you ascend to the surface.

These stops give the nitrogen that's built up in your body during the dive time to slowly escape from your organs and tissue. If you simply pop up to the surface after a long dive all this nitrogen will be suddenly expelled and you get decompression sickness - aka the bends. It's not pretty! It's like opening a fizzy drink that's been shaken up. Unscrew the top gradually... no problem. Take the top off quickly... very messy.

Well it's the same when you're diving at depth for any length of time... only it's your vital organs. Consequently, it's a good deal messier.

This is why your bezel only turns anti-clockwise - so that if you accidentally nudge it while underwater your decompression stop will get longer (hence safer) rather than shorter (hence more dangerous).

Hope this makes sense.

ahhh, Thank you for the explination.

[snow_rocks]

Originally Posted by jasonpage

This is why your bezel only turns anti-clockwise - so that if you accidentally nudge it while underwater your decompression stop will get longer (hence safer) rather than shorter (hence more dangerous).

Sorta, but not quite. The bezel is for tracking time underwater for the duration of the dive. If the bezel got knocked accidently, your dive time would be shorter, not longer (big problem!)

1680 had bi-directional bezel, one before yours.

[jasonpage]

snow rocks... you are absolutely right!

I was just about to go to bed and was looking at my own Sub when suddenly realised I'd been talking nonsense.

I rushed back to the computer... and I hope I haven't sent anyone to a watery grave.

As you say, you use the bezel to set your maximum dive time (based on your maximum depth and the volume of air in your cylinder).

Then if your bezel gets knocked your dive time will only ever get shorter - so you'll always have enough air to get to the surface!

Sorry if I've confused anyone.

[snow_rocks]

Originally Posted by jasonpage

snow rocks... you are absolutely right!


As you say, you use the bezel to set your maximum dive time (based on your maximum depth and the volume of air in your cylinder).

Then if your bezel gets knocked your dive time will only ever get shorter - so you'll always have enough air to get to the surface!

Still WRONG! Your dive time is the amount of time from the time you submerge until you surface. At 100 ft (33 m), you can stay a certain amount of time, not bottom time, (I think it's 20 min.) without any decompression stops. That is what the bezel is for, for elapsed dive time, not so that you have enough air. Not everyone consumes the same amount of air during the same dive. That is why there is a pressure gauge attached to the tank

[dskjl]

Wow, lots of information and freidly banter, thanks to all for your advise and explinations.

[Rikki]

Ok we'll get this straight it's to time your bottom time the deepest part of your dive. You have a safe bottom time at certain depths which varies on the depth. Say you're diving to 100' you have 25 minutes before you have to be back to at least 10' or if you go past that time and ascend you will get bent. You set the bezel to 25 minutes that time includes your descent and ascent time so if the bezel gets nudged it shortens the time giving a safety margin instead of a disaster margin. That's why it only turns i n one direction. Been diving for 40 years to depths of 260'. Rik the watchmaker

[jasonpage]

Sorry Snow Rocks but not quite sure of the point your making.

And Rikki... I think I see the point you are making. But I don't see why you think I'm wrong (second time around at least!)

My point is this...

Suppose I'm diving on air wearing a 12L cylinder filled to 232 bar. That gives me (12 x 232) 2784L of air. And I know the max depth I'm going to be diving to - in this case say 30m.

Using dive tables I work out that my no stop time (max time I can be at 30m without decompression) would be 20 mins.


I want to return to the surface with a reserve of 50L of air still in my cylinder. So I'm going to use 2734L for my calculations.

Most divers allow for a breathing rate of 25L per minute (this is quite generous but it allows for exertion). At my maximum depth (30m) the pressure will be 4 bar so I will be breathing (4 x 25) 100L of air per minute.

I know I'm staying down their for 20 minutes so on this basis I'll need 2000L of air. I'm planning to go in with 2734L + reserve. So I know I have enough air.

I now set my watch to 20mins. This records my dive time. If it gets nudged it gets shorter - hence safer.

By doing it this way - as long as I don't go deeper than my planned max depth - I can't get the bends and I can't run out of air.

This is a no stop dive - but one can plan a dive with deco stops in exactly the same way using the same principles. It's a very conservative way of planning a dive (it assumes for instance that you bomb down to your max depth and spend you whole dive down there) but it's very safe.

Anyway any confusion is entirely down to me and the inaccuracy of my initial post. That will teach me to nose around forums at 2 in the morning when I should be in bed!!

[snow_rocks]

Originally Posted by Rikki

Ok we'll get this straight it's to time your bottom time the deepest part of your dive. You have a safe bottom time at certain depths which varies on the depth.

This part of your post is misleading. Bottom time is not the same as dive time. You can spend all of your time at 30 m, or 1 minute at 30 m, then the rest of the time at 15 m; your total dive time (submerging and surfacing) is still 25 minutes, because you dove to 30 m.

The rest of your post is accurate, except the 10 feet of water part. Never heard of that.

As far as calculating volume of air (Jasonpage) for a dive, it makes since as an extra safety precaution, but most divers are sport divers (max. depth 130 ft), and with experience that a 3000 psi tank should get them on the boat with 500 psi still in the tank.

Obviously, we are covering more than the original question. Rolex corrected the bi-directional bezel with the uni-directional bezel for safety reasons involving the sport of diving!

[jasonpage]

Experience is not what gets sports divers back into the boat. That's what dive computers are for! With a dive computer you don't need to do this type of calculation. And you don't need a watch. But in the days before computers this is how it was done... and this is at the end of the day why divers needed watches.

And for the record, calculating the amount of gas you need is an essential part of the calculation.

Rikki's point about bottom time isn't as daft as you suggest (in my view). Once you've got three metres the dive is effectively over. You might have a brief safety stop here but any serious decompression will need to be done at greater depth.

Strictly speaking, of course, you are right about the distinction between bottom/dive time. But I think you are missing Rikki's point and (correct me if I'm wrong Rikki!) he is approaching this from a more practical point of view. As a diver, if you are doing anything even moderately interesting, 3m effectively is the surface - it's irrelevant to your calculations!!

The dive plan I gave by way of example was, as I said, very conservative. By using a "bottom time to 3m" as Rikki does you can start to trim it - to make your dive last longer and create a more realistic dive profile. So what he is saying does make sense from a practical point of view.

Again, all this is pretty academic. Especially in a watch forum! These are "old school" diving skills but in the days before dive computers a dive watch played an essential part in planning a dive.

At the end of the day, if you know how much gas you've got and you know (or simply decide) your max depth, all you need to dive safely is a watch.

And of course that watch should be a Rolex Sub!

[snow_rocks]

Okay, once again, dive time is not bottom time to 3 m or the surface, nor is it the time spent on the bottom or a given depth. It is the time spent from surface to a given depth to resurfacing.

Rik was correct in the 2nd part of his post, the 1st part is stated incorrectly.

I'll take my experience ('78 NAUI certified at Underwater Explorers in Ft. Myers) over a dive computer to get back into the boat. Seriously, are you kidding with that statement?

[Rikki]

Ok let's do this again hehe when I say bottom time I mean the max depth of your dive profile is what you use to calculate total dive dive. When you dive the axiom is plan your dive and dive your plan. The 10 foot stop is a safety stop being the last depth of a decompression dive that you stop at when doing a sequenced decompression dive. I always stop at 10 feet for a few minutes air content not withstanding as a safe stop. It's what I was taught at Naui and Ymca classes. Coming from New England originally,most all of my dives were decom dives in a dry suit with double 80's. Hope that gets it done Rik the watchmaker

[snow_rocks]

Originally Posted by Rikki

Ok let's do this again hehe when I say bottom time I mean the max depth of your dive profile is what you use to calculate total dive dive. When you dive the axiom is plan your dive and dive your plan. The 10 foot stop is a safety stop being the last depth of a decompression dive that you stop at when doing a sequenced decompression dive. I always stop at 10 feet for a few minutes air content not withstanding as a safe stop. It's what I was taught at Naui and Ymca classes. Coming from New England originally,most all of my dives were decom dives in a dry suit with double 80's. Hope that gets it done Rik the watchmaker

That makes more sense, especially concerning decomp dives. I don't envy your New England experience, with the dry suit, but the lobster was probably excellent!!!

[DRAWTOOL]

Originally Posted by jasonpage

Experience is not what gets sports divers back into the boat. That's what dive computers are for!

I have to disagree, in most cases it's the Beer and the Bikinis in the boat that gets them back in.

[jasonpage]

As I said, Snowy, technically you are correct. I just think you're missing the bigger picture here.

It's like when you say: "That is what the bezel is for, for elapsed dive time, not so that you have enough air."

Well, yes. A watch is there to tell the time. But of course, the moment you stick your head underwater time is meaningfully related to air consumption. And this is how we plan dives. I'm surprised that as an experienced diver you'd be quite so literal on this point.

Maybe we disagree on this. However, much of this stems from my original inaccurate post ... so what do I know?!