Saw tooth profiles.

[ratcliffe]

May I ask what might be a really thick question ?

Please smack me if I'm talking rubbish as usual


If DIR diving subscribes to doing definite things in definite ways, with diving equipment, styles, procedures etc, then how can Deco on the Fly be an acceptible method ? Surely everything must be "written in stone" as to what you are planning to do ?

I am genuinely confused here, as I assume Deco on the Fly means that you can change it as you go, (as opposed to making it up as you go along, but you know what I mean) ?

Thanks!

[Clare Gledhill]

Deco on the fly means simply to swim as you deco - nothing more although the phrase is so often used incorrectly on here and other internet boards.

In a cave, lets say you want to do a nine meter stop for two minutes. You look ahead and the passage seems level so you indicate to your team that you are calling two minutes of deco, note the time, but keep swimming.

Lets say that after one minute the passage starts to go up. You will stop and sit out the remaining minute as to proceed would violate your decompression ceiling.

What you refer to is ratio deco (sort of) or decompression based on the actual dive. We have a knowledge of the decompression obligations we will face from certain profiles and by keeping an eye on average depth can decide how much deco we need to do on the dive.

If we want to pad it a little we can. If any member of the team wants to call additional time or additional stops we can. Writing your plan in stone would mean that you have few options if things don't go as planned - and that wouldn't by DIR either would it?

[ratcliffe]

Thanks Clare, your last comment was exactly where I was confused as neither method seemed to look right based on the little I know about the DIR approach.
So the DotF method is basically the same as bimbling about on the 6m ledge at Stoney doing something whilst your safety stop clears in the background, rather than stopping dead and counting 3 minutes. I appreaciate its more advanced that that, but its basically the same idea, just in the team environment, yes ?

Thanks for that, I've always assumed that DotF was much more than it really is, its just kind of logical really, and most divers probably do it on occasion without knowing it really has a name.

Just another unrelated question, but it interests me... you say that any diver can call some extra padding or additional stop if they decide it is needed, but what would happen if someone indicated that they were planning to not do a stop as they didn't think it merited it. (I know that this basically wouldn't happen with the way it works, but I just wondered how it would be handled). I assume the other diver would indicate back no, we are stopping here, and the first diver would accept that so that the team stays together ?

[Clare Gledhill]

Originally Posted by ratcliffe

So the DotF method is basically the same as bimbling about on the 6m ledge at Stoney doing something whilst your safety stop clears in the background, rather than stopping dead and counting 3 minutes. I appreaciate its more advanced that that, but its basically the same idea, just in the team environment, yes ?

Nothing more advanced than that at all my friend. It's not rocket science

Just another unrelated question, but it interests me... you say that any diver can call some extra padding or additional stop if they decide it is needed, but what would happen if someone indicated that they were planning to not do a stop as they didn't think it merited it. (I know that this basically wouldn't happen with the way it works, but I just wondered how it would be handled). I assume the other diver would indicate back no, we are stopping here, and the first diver would accept that so that the team stays together ?

It is important that everyone is happy with the deco called. If someone calls more than expected it MAY be questioned...

(as in - are you sure you worked that out right? - 50 minutes at 6 after a 10 meter dive seems a tad excessive )

...but we will stay there until everyone is happy to come up.

So your way of explaining it is pretty spot on.

[ratcliffe]

Thank you for the explanations Clare, I understand now

[Janos]

Originally Posted by Clare Gledhill

Sorry - been diving.

That's a very good excuse. How was the dive?

I guess my question about saw-tooths is that knowing what I know about deco theory, I would expect to do more deco for a saw-tooth profile than at constant average depth.

Eg, if I was in a cave that varied between 45m and 25m (with an average depth 35m) then I would expect to do more deco than if I kept a constant depth in the ocean, diving a wreck at a constant depth of 35m.

Would you change your deco schedule if you'd done a saw tooth profile?

Janos

[Ahmed Adly]

sheesh.... Even the average depth line is crooked!

[Clare Gledhill]

Originally Posted by Ahmed Adly

sheesh.... Even the average depth line is crooked!

That's the temperature Ahmed

[MATTBIN]

Clare
how do you work out the average depth? Is it a computer read out as you go, I dont think my Suunto gives that info, what computer do you use.

Matt

[Clare Gledhill]

I now have an Aladin Tec 2G which gives average depth but to be honest it is not that difficult to gauge it for yourself - certainly I've had to for the last 500 odd dives I've done. We wouldn't want to rely on a computer would we

In cave the variation is clearly more than it is on a square profile dive but try this. Have a look at the profile yourself and decide roughly what you think average is. It is easier when it is graphic like the profile but you can build a mental picture of the dive as you go with a bit of practice, that you can then base depth upon.

If you are not sure, just err on the side of caution. This dive was a dpeth average of 10 metres according to the computer but I would have called it on 12. If in doubt go lower.