Suggestions for getting my first dive computer

[KenGordon]

Can please post some citations of your evidence for this?

Also, for the record, I have never told anyone to buy an aggressive computer. I have said (repeatedly) that it does people a disservice to tell them that any aspect of their computer is something they should not worry about. Telling people "don't worry about that. It won't matter to you" or "you aren't smart enough to understand that bit" is just wrong. Give people the info and let them decide for themselves what is important to them.

The algorithm may not matter - to YOU. AI may not be useful - to YOU. AI may not be worth the price premium - to YOU. But, I think is simply wrong to make those judgments and then foist them onto other people. Especially new divers who don't have the experience to appreciate that some "expert's" statement that "AI is not worth it" simply means that it is not worth the price, based on that person's needs and budget. It's too easy for them to take a simple statement like that as "there is no value to anyone in having it" - which is patently untrue.

You say "the algorithm doesn't matter" and they don't appreciate that it doesn't matter to you because you are trained for deco, and/or it took you 5 years to get to the point of being able to stay down to your NDL, or whatever your various reasons. You don't know the OP. You don't know that your reasons fit them. If you have facts to support your statement that the algorithm doesn't matter, then share them with us all. If it's just that you have some "feeling" that it's significantly more likely to get them bent, then you could at least do them and the rest of us the courtesy of making it clear that saying the algorithm doesn't matter is based on no facts and just a feeling that you have. A hunch. Something you "think". Whatever. If Simon Mitchell "thinks" something about deco. Or David Doolette. Or a list of others, I would take that seriously. If your credentials are on par, that what you "think" should be taken as legitimate evidence by a new diver, with no facts cited to support it, then please share them. Otherwise, I will continue to try and share what facts and hard data I can, so that new divers can make their own informed choices, instead of just taking my or anyone else's word for what matters (or should matter) to them.

Earlier in this thread it was explained that resort diving is actively designed to prevent the punters getting into deco.

The logic is not a feeling. If the dive is limited by design, gas, or other limit then the NDL does not figure.

Ps I like AI.

 

[packrat12]

Stuartv - There is a line based on physiological parameters and physical parameters which when crossed you WILL get hit with DCS. A 'liberal' computer will take you closer to that line. A conservative computer will be further away from that line. On a generic statement that is a FACT. The best we can do is model where this line is. Many models use the M-Value line to approximate this. It is possible that the true (personal for that moment) line has already been crossed or may be even not near it. You just do not know. The incidence of DCS is very low. How much of this 'low' is because most of us ignore some form of nits until it becomes 'full blown' DCS? You might want to read and understand the article "Understanding M-Values" by Erick Baker more. It appears that you do not understand the difference between a safety margin and how it pertains to a liberal or conservative algorithm. There are many ways to calculate NDL times and each will come up with different results. As long as they do not cross you line, you will not get DCS. But that does not mean the same as one having a safer profile or not. The one that stays further away from the 'true' m-value line IS safer.

Many of us, and I am sure Ken Gordon is one of them will put the algorithm of a computer towards the very bottom of our selection. Functionality, readability etc are much higher and will provide a much better user experience then a difference in liberal vs conservative computer.. A few extreme divers believe that they are cheated out of minutes if they cannot be the longest in a dive. Funny way of diving. Many are probably also the type that want to reach the deepest depth on the dive also. Maybe it is my maturity in diving but I care for neither now. I like to reach certain points in depth and time but I will often not even reach my planned depth or time in a technical dive. I am there for enjoyment. BTW, the Shearwater computers are very conservative without GF adjustment in my experience. Even adjusting GF it may not be the most liberal anyway. And from the sounds of it, why not just recommend everyone buy a Shearwater Perdix - It is what most of the 'I want a liberal computer' group sounds like. After all the Perdix will take any diver from novice to expert without ever having to buy another one!

 

[KenGordon]

btw, how about you show me evidence that an aggressive computer is never going to give an NDL that leads to an injury?

This is clearly a rubbish rhoterical position so how about you stop using it?

 

[drrich2]

"Also the obsession with NDLs is bogus, the proper thing is to just do (short) deco dives.The training that means that people cannot do that is inadequate. All these inadequate divers needing hand holding leads to a poorer experience for those that are not trained to the lowest common denominator when they visit holiday destinations."

Inadequate or not, basic ow and aow training today for legions of people does not deem planned deco. diving as acceptable. It's been my impression of Caribbean dive boats they don't want customers doing deco. dives on recreational trips.

A person headed to Florida and the Caribbean planning recreational boat dive trips with deco. would find getting a compatible instabuddy difficult and could run afoul of boat operator policy.

There's more to the world than Florida and the Caribbean. Those of you who've been far ranging, how does that work at Red Sea, Palau, PNG, Yap, the U.K., etc...?

 

[scubadada]

Because I genuinely think those thelling them to buy aggressively computers are hurting people. Given a significant population diving to longer NDLs some will get bent. Something like one in five of these new divers will have a PFO and so eventually they might get bitten by diving to longer NDLs.

Also the obsession with NDLs is bogus, the proper thing is to just do (short) deco dives. The training that means that people cannot do that is inadequate. All these inadequate divers needing hand holding leads to a poorer experience for those that are not trained to the lowest common denominator when they visit holiday destinations.

I'm sorry, Donald Trump thinks he lost the popular election in the US because 3-5 million people voted illegally. Of course, he has absolutely no evidence to support his beliefs. You think that more liberal, commercially available, dive computers result in DCS. You, also, have absolutely no evidence to support your belief. Being intuitively obvious to you, does not make it true. DAN Project Dive Exploration has been running since 1999 and probably has had the best chance of demonstrating any significant difference in the rate of DCS associated with decompression algorithm. This evidence has not been forthcoming. It may be that all commercially available decompression algorithms are sufficiently safe that no difference between them can be demonstrated.

I appreciate your comment regarding decompression, I do relatively short deco on about 5% of my dives. With the exception of some of your continuing BSAC training, deco is not taught or recommended by other agencies for recreational diving. Regardless, we are discussing first dive computer purchase for relatively new divers, diving within generally accepted recreational parameters.

 

[KenGordon]

I'm sorry, Donald Trump thinks he lost the popular election in the US because 3-5 million people voted illegally. Of course, he has absolutely no evidence to support his beliefs. You think that more liberal, commercially available, dive computers result in DCS. You, also, have absolutely no evidence to support your belief. Being intuitively obvious to you, does not make it true. DAN Project Dive Exploration has been running since 1999 and probably has had the best chance of demonstrating any significant difference in the rate of DCS associated with decompression algorithm. This evidence has not been forthcoming. It may be that all commercially available decompression algorithms are sufficiently safe that no difference between them can be demonstrated.

I appreciate your comment regarding decompression, I do relatively short deco on about 5% of my dives. With the exception of some of your continuing BSAC training, deco is not taught or recommended by other agencies for recreational diving. Regardless, we are discussing first dive computer purchase for relatively new divers, diving within generally accepted recreational parameters.

How does an example of a diver doing a profile on a recreational diving computer within NDL limits yet still getting bent sound as evidence? How about about 30% of all bent divers being within such limits (in the U.K.) sound?

We are not talking about different algorithms, but the setting for those algorithms. Are you also going to claim that the likelihood of DCS somehow decreases with time spent at depth?

Disolved gas increases with time, the disolved gas models say there is an upper limit on how much overpressure is safe. Thus longer exposure is more dangerous. That is a core feature of these models. It is widely accepted that the very early black and white limits are not correct and that there is a spread of probability of a bend and both sides of the 'limit' can lead to either outcome.

Nobody can actually run a proper comparative study on recreational diver DCS as other factors usually swap the figures. Thus a very large number of samples would be required, not just the few hundred that NEDU used for the deep stops study.

Can you provide evidence that there is zero risk from diving these profiles?

Let me be clear, I think people get bent on conservative NDL dives too, just they are less LIKELY to be bent than on the aggressive ones.

 

[scubadada]

How does an example of a diver doing a profile on a recreational diving computer within NDL limits yet still getting bent sound as evidence? How about about 30% of all bent divers being within such limits (in the U.K.) sound?

We are not talking about different algorithms, but the setting for those algorithms. Are you also going to claim that the likelihood of DCS somehow decreases with time spent at depth?

Disolved gas increases with time, the disolved gas models say there is an upper limit on how much overpressure is safe. Thus longer exposure is more dangerous. That is a core feature of these models. It is widely accepted that the very early black and white limits are not correct and that there is a spread of probability of a bend and both sides of the 'limit' can lead to either outcome.

Nobody can actually run a proper comparative study on recreational diver DCS as other factors usually swap the figures. Thus a very large number of samples would be required, not just the few hundred that NEDU used for the deep stops study.

Can you provide evidence that there is zero risk from diving these profiles?

Let me be clear, I think people get bent on conservative NDL dives too, just they are less LIKELY to be bent than on the aggressive ones.

As you point out, divers get bent following all decompression algorithms and some of these episodes are unexplained. Clearly, there are many variables, both personal and environmental, that contribute to these events. As I pointed out, it may be that all commercially available decompression algorithms are sufficiently safe that no difference between them can be demonstrated. Being a physician and scientist, I am sensitive about having evidence to support the conclusions I draw and the advice I give. You have beliefs, no evidence is necessary. There is risk in all diving, those of us who dive, accept it.

 

[KenGordon]

"Also the obsession with NDLs is bogus, the proper thing is to just do (short) deco dives.The training that means that people cannot do that is inadequate. All these inadequate divers needing hand holding leads to a poorer experience for those that are not trained to the lowest common denominator when they visit holiday destinations."

Inadequate or not, basic ow and aow training today for legions of people does not deem planned deco. diving as acceptable. It's been my impression of Caribbean dive boats they don't want customers doing deco. dives on recreational trips.

A person headed to Florida and the Caribbean planning recreational boat dive trips with deco. would find getting a compatible instabuddy difficult and could run afoul of boat operator policy.

There's more to the world than Florida and the Caribbean. Those of you who've been far ranging, how does that work at Red Sea, Palau, PNG, Yap, the U.K., etc...?

All the warm water places I have dived try to prevent deco diving by choice of site, gas supply and dive times. More so in the Caribbean than in Egypt. In the U.K. you have the boat for the day mostly and they are not concerned with your plan other than wanting to know how long to wait before calling the coastguard.
Some UK skippers will give advice (tell white lies) designed to prevent high risk dives. Some will have a full and frank discussion about the pros and cons given who they have on the boat. No skipper wants bodies, many have had bodies and know what it is like.

The answer to short NDLs is not longer NDLs. It is Nitrox, and potentially doing stops. Otherwise risk goes up. But if NDLs never figure because the dive op has decided the route starts deep, get shallow and stays shallow then gas becomes the limit and the computer algorithm becomes unimportant.

What is deco? What are the OPs trying to prevent? They want divers who are not bent. Do they really care if that requires 3 minutes compulsory deco on a Suunto or 3 minutes of DSAT safety stop for the same bottom time?

 

[KenGordon]

As you point out, divers get bent following all decompression algorithms and some of these episodes are unexplained. Clearly, there are many variables, both personal and environmental, that contribute to these events. As I pointed out, it may be that all commercially available decompression algorithms are sufficiently safe that no difference between them can be demonstrated. Being a physician and scientist, I am sensitive about having evidence to support the conclusions I draw and the advice I give. You have beliefs, no evidence is necessary. There is risk in all diving, those of us who dive, accept it.

You seem to be claiming that diving is safe and that those following computers will not get bent. But people do get bent. I am saying that following a computer is no guarantee of safety but that some profiles are riskier than others. The longer the bottom time the higher the risk. That is widely accepted. Do you dispute that? Is it too much of a leap to see that those exploiting the longer NDLs are at greater risk, all other things being equal?

Do you have evidence that longer NDLs are as safe as shorter ones? That is the advice you give.

My advice is buy the cheapest one because these things do not actually matter.

 

[dmaziuk]

"Also the obsession with NDLs is bogus, the proper thing is to just do (short) deco dives.The training that means that people cannot do that is inadequate. All these inadequate divers needing hand holding leads to a poorer experience for those that are not trained to the lowest common denominator when they visit holiday destinations."

Inadequate or not, basic ow and aow training today for legions of people does not deem planned deco. diving as acceptable. It's been my impression of Caribbean dive boats they don't want customers doing deco. dives on recreational trips.

A person headed to Florida and the Caribbean planning recreational boat dive trips with deco. would find getting a compatible instabuddy difficult and could run afoul of boat operator policy.

In my limited experience I have not had a Caribbean boat operator ask. I had one DM warn about computers possibly "not like" the 130' bottom on El Aquila wreck, plus when I'm dripping wet or too lazy to write down dive time and max depth in the boat's paper log (when there is one), I've shown them the computer so they'd write it down themselves. When I run into one that has a policy issue, I'll find myself another boat.

I did, thanks to one of these threads, skim through my PADI OW manual the other day. In 20/20 hindsight it is fairly clear that PADI OW course is teaching no stop diving, and that in the context of no stop diving, a mandatory stop is regarded as diving beyond one's training and as emergency procedure. It isn't really based on risks of DCS, at least not directly -- the stated policy is we train you for no-stop, you're not qualified to do stops. Put a bunch more dollars in, get tech trained, and then we won't have a problem with your yes stop diving, regardless of how you might come up with those stops.

The part where a computer will actually calculate a safe ascent schedule for you and you only need to make sure you have enough gas (and a plan for if the computer packs it as per Murphy's Law) is not part of that policy. How this rationally leads to the obsession with NDLs is quite beyond me, so "bogus" would be one correct word to describe it.