Suggestions for getting my first dive computer

[scubadada]

TBH I am just poking fun at the inadequacy of a system where staying down longer and surfacing directly is allowed but staying down the same time and doing the stops is not.

Maybe I should print out some tables that allow 30 minutes at 30m but 'recommends' a 20 minute safety stop. Then we'd all be golden

Neither SSAC And BSAC first level courses are where anyone stops their training. To have a choice of interesting sites requires more that 15 or 20m and with that comes deco training. There is no arguing that an entry level diver is qualified beyond those depths like suggested for PADI etc OW. This means that all the regular divers can do deco. Maybe that is why they all buy Suuntos.

Hi Ken,

It's good to be honest. I have no dog in the training contest. I was trained by LA County in 1970, the training was rigorous. This included contingency deco using the USN tables. I was recertified by PADI in 1997 when my son was 12. Though this may be incorrect, and I invite corrections, it appears that the BSAC Sports Diver certification includes simulated deco, but not real deco. More mentor training would be required before a Sports Diver would be able to dive to maximum depth and do staged deco. I applaud @offfi for his recommendation of Oceanic entry level computers. They offer 2 decompression algorithms, each with a conservative setting. From liberal to conservative these include DSAT, PZ+, DSAT with conservatism, and PZ+ with conservatism. This spectrum should satisfy almost anyone and could closely match all other decompression algorithms.

I still do not understand why you resist that divers understand decompression and decompression algorithms before they choose their first dive computer. It does not seem like you are against technology or knowledge, in general

Good diving, Craig

 

[KenGordon]

Hi Ken,

It's good go be honest. I have no dog in the training contest. I was trained by LA County in 1970, the training was rigorous. This included contingency deco using the USN tables. I was recertified by PADI in 1997 when my son was 12. Though this may be incorrect, and I invite corrections, it appears that the BSAC Sports Diver certification includes simulated deco, but not real deco. More mentor training wold be required before a Sports Diver would be able to dive to maximum depth and do staged deco.

<snip>

I still do not understand why you resist that divers understand decompression and decompression algorithms before they choose their first dive computer. It does not seem like you are against technology or knowledge, in general

Good diving, Craig

I am not against knowledge, but the fact is 90% or more of new divers are not educated at all about deco or the theory. Thus they are not ina possitionto evaluate the risks. Really all divers evaluate deco risk by experience. I am happy diving such and such setting because I have done it before and it was ok. I have seen other people do similar dives and it was ok. I have done other dives before with this computer and I was ok then.

New divers do not have that experience.

They almost certainly do not know people who have ended up in hospital diving profiles they would consider average.

BSAC Sports divers do not do deco before they are qualified. As Ocean divers it is not allowed. They do have to show that they can plan and execute a deco dive, it is just that the dive will not have been all spent at depth. ALso the limit during training being 20m means it is not 'for real'. 'Mentoring' is REQUIRED for depth extension but not for deco. However most, at least many, will be doing deco dives soon after. In my club I cannot think of a sports diver who has been a sports diver more than a season who had not done deco dives. That is not to say that they all do them all the time but they are genuinely competent to do them.

Similarly, on TDI courses I have done the plan may be 30 minutes at 45m but somehow something always comes up so the actual profile isn't quite so committed...

 

[scubadada]

I am not against knowledge, but the fact is 90% or more of new divers are not educated at all about deco or the theory. Thus they are not ina possitionto evaluate the risks. Really all divers evaluate deco risk by experience. I am happy diving such and such setting because I have done it before and it was ok. I have seen other people do similar dives and it was ok. I have done other dives before with this computer and I was ok then.

New divers do not have that experience.

They almost certainly do not know people who have ended up in hospital diving profiles they would consider average.

BSAC Sports divers do not do deco before they are qualified. As Ocean divers it is not allowed. They do have to show that they can plan and execute a deco dive, it is just that the dive will not have been all spent at depth. ALso the limit during training being 20m means it is not 'for real'. 'Mentoring' is REQUIRED for depth extension but not for deco. However most, at least many, will be doing deco dives soon after. In my club I cannot think of a sports diver who has been a sports diver more than a season who had not done deco dives. That is not to say that they all do them all the time but they are genuinely competent to do them.

Similarly, on TDI courses I have done the plan may be 30 minutes at 45m but somehow something always comes up so the actual profile isn't quite so committed...

So what are we arguing about? You dive your computer's algorithm and, either stay within NDL, or do the requisite stops. A more liberal algorithm simply allows you to stay within NDL longer, prior to required stops. Few would argue the more liberal algorithms are not safe, right?

 

[doctormike]

So what are we arguing about? You dive your computer's algorithm and, either stay within NDL, or do the requisite stops. A more liberal algorithm simply allows you to stay within NDL longer, prior to required stops. Few would argue the more liberal algorithms are not safe, right?

I haven't the slightest idea at this point what we are arguing about. Advice to just make the stops if you are over NDL doesn't seem to make sense in the context of the New Divers forum and the OP having less than 25 dives.

I don't think that more liberal algorithms are "not safe" in an absolute sense - any modern recreational dive computer should get most divers out of the water with a statistically tiny chance of DCS. But the only thing that the computer knows is depth, time and mix. And there is a lot more that goes into decompression stress than those three variables.

Any algorithm just draws a bright line through a grey area. But a more conservative algorithm is always going to give you less decompression stress than a more liberal algorithm. Whether or not that is clinically significant depends on all of those other factors that the computer doesn't know about.

 

[KenGordon]

So what are we arguing about? You dive your computer's algorithm and, either stay within NDL, or do the requisite stops. A more liberal algorithm simply allows you to stay within NDL longer, prior to required stops. Few would argue the more liberal algorithms are not safe, right?

I am saying you do not need an aggressive computer to get the bottom times you require.

I am also arguing that divers in general and new divers in particular do not know the level of risk from decompression and so cannot judge whether a computer is safe or not. That will depend on THIER idea of safe. If that is zero risk of a bend then none are safe.

This is a probability thing. Enough people doing a 4 minute longer NDL will lead to extra bends. So that NDL was not 'safe' for that diver that day.

Now if those long NDL divers did some extra time at 3 to 6m they will reduce the chances of a bend. I believe you have said you do that.

Similarly, if a conservative computer diver did the same bottom time and did the mandatory stops they will get out the water at about the same time with about the same risk.

And yes, a diver needs some training to do that but that is about the diver and not the computer. And in any case the limits are likely to be gas in the case of a new diver.

Consider the concequences for a minute. When are you likely to discover what aggressive means? How about a four dive a day live aboard with non nannying guides. I was one one in Egypt a couple of years back. Anyone getting bent would have meant a 24 steam back to a chamber. My mate who got bent on a nonstop dive last year was lucky that he was in the U.K. so had a helicopter take him to a chamber and then had all the technology and skills available a major economy to treat him with my a couple of hours. Do we fancy this in some resort someplace after a long time bouncing about on a boat?

 

[Neilwood]

I am saying you do not need an aggressive computer to get the bottom times you require.

I am also arguing that divers in general and new divers in particular do not know the level of risk from decompression and so cannot judge whether a computer is safe or not. That will depend on THIER idea of safe. If that is zero risk of a bend then none are safe.

This is a probability thing. Enough people doing a 4 minute longer NDL will lead to extra bends. So that NDL was not 'safe' for that diver that day.

Now if those long NDL divers did some extra time at 3 to 6m they will reduce the chances of a bend. I believe you have said you do that.

Similarly, if a conservative computer diver did the same bottom time and did the mandatory stops they will get out the water at about the same time with about the same risk.

And yes, a diver needs some training to do that but that is about the diver and not the computer. And in any case the limits are likely to be gas in the case of a new diver.

Consider the concequences for a minute. When are you likely to discover what aggressive means? How about a four dive a day live aboard with non nannying guides. I was one one in Egypt a couple of years back. Anyone getting bent would have meant a 24 steam back to a chamber. My mate who got bent on a nonstop dive last year was lucky that he was in the U.K. so had a helicopter take him to a chamber and then had all the technology and skills available a major economy to treat him with my a couple of hours. Do we fancy this in some resort someplace after a long time bouncing about on a boat?

This applies to my diving - I knew before starting to dive that I would want to do these sorts of trips. I also knew that my fitness wasn't probably the best and that I am not as young as I used to be (who would have thought it?). Do I want to push the limits when medical assistance is an unknown time away? As you say, the risks diving in the UK are fairly benign in that an airlift is probably not far away and there are sufficient chambers readily available and within reasonable reach. Therefore if I get bent, I am reasonably safe by comparison to diving elsewhere in the world where access is not as readily available.

I also understand that decompression theory is accepted by the "experts" as just that - a theory. The experts don't know 100% what the entire mechanism for DCS is or how to accurately predict, for a particular individual, when that person will exhibit DCS. They have best guesses based on statistical analysis and empirical data which provide a "best guess" as to when a statistical majority of people will be "safe" based on a number of parameters such as time, depth, ascent rate, "risk factors" such as sawtooth profiles etc.

The whole subject , for me boils down to one simple fact (which I don't think anyone can actually argue) - what is unknown for all divers (that have not actually been bent) is exactly where your personal threshold for DCS actually is on any given day. Although NDL is a hard and fast number provided by whatever algorithm we choose to use, the threshold for DCS is not. It is at best a line in the sand and one that can shift depending on a number of factors on the particular day such as fatigue, cold, hydration etc. The worst thing about that line in the sand is that no one actually knows where it sits on any given day until they have gone over it and got bent or done hundreds of dives where they have analysed their own bodies for signs and symptoms (which may or may not be masked by other things such as muscle pain from lifting heavy gear). If I can't see where the danger line (DCS threshold) is, I choose to place my safety line (NDL) as a conservative distance from where it might be as opposed to making a more liberal assumption.

Your choice with regards to risk/reward may vary from mine.

 

[drrich2]

In which case a computer that offered 2 algorithms, one liberal for more benign condition diving, and one more conservative for more adverse condition diving, would seem the logical choice, at least from that perspecitve?

Richard.

 

[Neilwood]

In which case a computer that offered 2 algorithms, one liberal for more benign condition diving, and one more conservative for more adverse condition diving, would seem the logical choice, at least from that perspecitve?

Richard.

I don't know where my threshold for DCS stands as a relatively new diver and as a 45 year old who is probably not as fit as I should be, I choose to make my choice as safe as I can.

When I say that UK diving is relatively benign it is due to the nature of emergency help (it is, to an extent, readily available at short notice) which would mitigate the effect of a DCS hit. The diving itself presents issues that are risk factors for DCS such as cold water, cold surface conditions, changeable weather conditions etc.

 

[Diving Dubai]

When I go on Liveaboards, even though when asked when I last dived I can say within the last 10 days, I alther my computer to make it more conservitive for the first couple of days.

Many people underestimate (in my opinion) the effects of traveling

Not only flying and feeling tired, but the change in climate, the change in diet and obviously dehydration. Often people are excited to be on vacation and only dive on them so may be more inclined to burn the candle at both ends (at least at the beginning)

We "know" That all of the above can have a contributory factor. Personally I'd rather have to come shallower a little earlier in the dive (generally I don't hit the NDL limit on the first couple of days though) than be medivaced off ruining the rest of the holiday for me and my wife.

Totally agree with @neilwoods philosophy

 

[stuartv]

I don't know where my threshold for DCS stands as a relatively new diver and as a 45 year old who is probably not as fit as I should be, I choose to make my choice as safe as I can.

Do you have an adjustable Conservatism Factor? Do you set it to its highest value? If you don't, are you really being as safe as you can? If you don't, how do you, personally, decide that the amount you are safer is enough, but more conservatism is not required?

When you set your computer to be "more conservative", are you decreasing your changes of DCS from 2% to 1%? From 0.2% to 0.15%? To borrow an earlier poster's analogy, how do you know whether you have moved from 1m away from the precipice to 2m away, or if you have moved from 1km from the precipice to 2km away?

I'm sincerely NOT trying to bash you or make light of how you choose to set your personal boundaries. I AM trying to highlight that it seems like some people are very quick to bash others for diving a "liberal" computer to its NDL while lauding others who choose a "conservative" computer, and yet none of us has any evidence to present that shows that one is truly any more effective at preventing DCS than the other. From the evidence that I'm aware of, these differences seem to be closer to the 1km vs 2km example than the 1m vs 2m example. I would love to see actual data on the subject, if anyone has any.