What's the deal with run times?

[pressure tested]

just been having a look at dive plans etc and has brought a question up on run times. For example:

depth time run time
30m 20min 20min
12m 5min 25min
9m 4min 29min
6m 6min 35min
3m 5min 40min

So if you were to work just on run times here you would start missing 30-40 seconds of deco on each stop.

In the time it takes you to leave 12m after 25min in the water you come up to 9m, this will probably be done quite slowly taking maybe 30 seconds. You are then arriving at this stop at 25:30. you then leave following run time at 29min, you have not then actually done the 4min you are mean to, then you will do the same on the next stop, this will all add up so you are missing perhaps 2 or 3 min in the end. Can someone explain this, as I know some people dive with only the runtimes written out, no actual deco stop times. I have been going not on run times but just timing the stops when I get there, can someone explain this runtime stuff to me.

P.S I know the stop times are not right I made them up!

[DanE]

The run time column you have is the time you leave that depth.

The time column you have is the stop time at that depth including the time it takes to travel from the previous stop to this one. They are not the time you actually spent stopped at a depth.

When calculating your plan, you should be aware of the ascent rates that you need to use between stop depths as the deco algorithm takes these into account when calculating the stops.

Don't want to be a nagging nanny, but if you are just starting into the world of decompression diving then I would recommend taking some kind of decompression procedures course.

HTH
dan

[pressure tested]

So how should it look.

All of the run time profiles I have ever seen never include extra time it takes to move from one stop to the next. They miss this out, this means in theory you have to get from one stop to the next instantaneously, which can never happen. Or is it seen as O.k to take 30 seeconds or so to get from one stop to the next without adding any time to your deco?

I have, but I was told that the depth changes are shallow so you go from one to another, without adding any time for the transition, but this does not seem right. So you recon add a minute on the run time for each depth transition, then you'll be nice and safe??

[wreckweasel]

No, as the previous poster said, the runtime ALREADY includes your travel time. So leave the stop when your runtime is up and move up to the next stop at the ascent rate you specified in the software/table/deco model.

A little knowledge is a dangerous thing, n'est pas?

[DanE]

In true blue peter stylie, here's a plan I made earlier....

Dec to 32m (3) Nitrox 32 10m/min descent.
Level 32m 36:48 (40) Nitrox 32 1.34 ppO2, 26m ead
Asc to 21m (41) Nitrox 32 -6m/min ascent.
Asc to 9m (44) Nitrox 50 -5m/min ascent.
Stop at 9m 0:46 (45) Nitrox 50 0.95 ppO2, 2m ead
Stop at 6m 11:00 (56) Nitrox 50 0.80 ppO2, 0m ead
Surface (58) Nitrox 50 -3m/min ascent.


So, I leave the bottom at 40 minutes and ascend to my first stop at 9m (there's a gas switch on the way as well) It should take me just over 4 minutes to get to 9m. If I got it right then I will wait at 9m for 46 seconds.
Next I ascend to 6m at 5m a minute. So it will take just under a minute to reach 6m. The combined time of that ascent and the time I spend at 6m is 11 minutes. So if it took me 40 seconds to travel from 9m to 6m, then I have 10 minutes and 20 seconds a 6m.

WARNING: I'm not sure if I've dived this plan. It is just an example! Please - nobody follow it!

dan

[pressure tested]

Originally Posted by wreckweasel

No, as the previous poster said, the runtime ALREADY includes your travel time. So leave the stop when your runtime is up and move up to the next stop at the ascent rate you specified in the software/table/deco model.

A little knowledge is a dangerous thing, n'est pas?

True, you wouldn't think I had done the course. Something to be said for taking your time over these sort of courses, I should think, then I wouldn't have had questions like this.

[DanE]

It might be worth giving your instructor a call and chatting over this stuff again, it's quite important. Certainly better than misunderstanding it and getting bent or worse.

dan

[londonsean69]

At these depths, and with the conservatism of most computers/programs, 30-40 sec won´t make much difference.

But ask you instructor about it.

If you were not clear on it when you finished the course then you weren´t taught properly.

Either that or you did the course and have never done any run-time dependent dives since

[wreckweasel]

The truth of the matter is that computers model something in a simple way... and we're not simple things. So as sean says, 30 secs wont kill you. As long as your deco is pretty much the right shape/duration you'll get away with a few bits here and there as long as you're reasonably conservative (its not a race).

The advise to speak to your original instructor is good... no one likes to think they've got a student running around who's not fully informed of the course content.

//Z

[Mal Bridgeman]

Originally Posted by wreckweasel

A little knowledge is a dangerous thing, n'est pas?

Especially a little knowledge of French .... it's n'est-ce pas !!

Couldn't resist that one Zak.