Temperature & Computer Algorithms

[Soggy_Diver]

After a weekend of diving in Tobermory, I have some questions about deep cold water dives and the algorithms that computers use to work out no decompression limits (better late than never!).

Cold water dives should be planned as if they are 10 feet deeper than their actual maximum depth. My dive computer, a Sherwood Profile, measures temperature, but as far as I can see from the specs, it does not take temp into account in calculating the time to the no decompression limit. Is that typical of dive computers, or is this because the Profile is a very basic computer?

To compensate for the temperature on cold water dives, I subtract a few minutes from the time to NDL that I see on the screen to bring it in line with a dive that is 10 feet deeper. Is that how other people are dealing with this?

 

[fisheater]

Why not ask the Sherwood representative whether or not your computer it takes temperature into account? It may, but it may not say one way or the other in manual.

 

[Diver0001]

After a weekend of diving in Tobermory, I have some questions about deep cold water dives and the algorithms that computers use to work out no decompression limits (better late than never!).

Cold water dives should be planned as if they are 10 feet deeper than their actual maximum depth. My dive computer, a Sherwood Profile, measures temperature, but as far as I can see from the specs, it does not take temp into account in calculating the time to the no decompression limit. Is that typical of dive computers, or is this because the Profile is a very basic computer?

To compensate for the temperature on cold water dives, I subtract a few minutes from the time to NDL that I see on the screen to bring it in line with a dive that is 10 feet deeper. Is that how other people are dealing with this?

As far as I know that's exactly what most people do. The method is unofficially known as "pad by gut feeling".

Most computers don't account for temperature. IIRC there was one from UWATEC that tried that along with a bunch of other bubble related penalties (maybe it was called Z-something but I'm not sure) but it was giving people such conservative numbers that it never became very popular.

The best way to get a ballpark figure for your NDL on a cold day is still the tables.

R..

 

[rstofer]

I don't know anything about your computer but my Dive Rite NiTek Duo allows me to enter a 'safety factor' between 0 and 2.

0: calculations are based on Buhlmann ZH-L16
1: calculations are based on one altitude rank higher than the dive was actually made
2: calculations are based on two altitude ranks higher than the dive was actually made

SF=0, 60 foot dive, NDL 49 minutes
SF=1, 60 foot dive, NDL 44 minutes
SF=2, 60 foot dive, NDL 39 minutes

But, it's up to me to change the SF.

Richard

 

[siikik]

I would have to say that a computer can't accurately adjust for temperature. After all, it is reading ambient temperature and has no clue what you are feeling. Perhaps you're in a dry suit and the cold water isn't affecting you. Too many unknowns and there would be far too many things to configure on the computer which may or may not eventually get it right... I've been on dives in the same spring with the same westuit and one time I'll be cold and the next I'll be fine, probably because I did just a wee bit more work. My point is there is no consistency so forget asking a computer to figure it out.

The only reference I've heard of suggesting any changes to dive tables is from a NAUI course that says that if you feel cold on a dive, you should add one full repetitive group letter to the dive. I suppose the equivalent setting for the computer would be to set it to the next lowest setting for nitrogen loading and/or PPO.



Ken

 

[Mr Carcharodon]

Did your dive computer ask you if you were wearing a 3mm wetsuit or dry suit before the dive. Did it ask you if if felt cold during the dive? If not how do you think the adjustment is going to be made?

 

[Soggy_Diver]

:thumbs-upThanks everyone, for your responses. My next question was going to be, if dive computers don't consider temp, why don't they? But you have answered that already.

 

[elan]

Did your dive computer ask you if you were wearing a 3mm wetsuit or dry suit before the dive. Did it ask you if if felt cold during the dive? If not how do you think the adjustment is going to be made?

Yes absolutely, My friend was diving Brockville in poor fitting rental 7 mm suit and got shaking after a second 30 min dive in 70F water. Yet we dove in Tobermory in 46F in dry suits and after the 3rd dive for 40 mins still felt like we could jump back in with no prob cold wise.

 

[GrandpaScuba]

... My dive computer, a Sherwood Profile, measures temperature, but as far as I can see from the specs, it does not take temp into account in calculating the time to the no decompression limit. Is that typical of dive computers, or is this because the Profile is a very basic computer?
...

All the high-end computers from UWATEC, starting with the Aladin Air-X and moving on through the "smart" series (SmartCom, Smart-Z, Smart-Tec...) and now into the Galileo series, all use water temp in their algorithm. These air-integrated computers also use "how hard you are breathing" in the algorithm and now, with the Galileo series, they also use your heart-rate, if you are wearing the included heart rate monitor.

 

[ianr33]

All the high-end computers from UWATEC, starting with the Aladin Air-X and moving on through the "smart" series (SmartCom, Smart-Z, Smart-Tec...) and now into the Galileo series, all use water temp in their algorithm. These air-integrated computers also use "how hard you are breathing" in the algorithm and now, with the Galileo series, they also use your heart-rate, if you are wearing the included heart rate monitor.

Could you point me towards the science behind the algorithms used?

or are they a complete WAG?