Computer recommendations for New Divers

[Gary_Ward]

You have made a blanket statement that I don't believe holds up to scrutiny. If I were to follow your advice driving a car on a road, in traffic, with an 80km per hour speed limit then going 79km and hour would be safe but going 40km per hour would be more safe. I believe however that going 40 would make you less safe because your car would be an impediment and would likely get hit by someone going twice as fast as you, going with the flow of traffic in my example is more safe.

Following the same analogy with diving if staying under M values is the rule then applying conservative gradient factor must be more safe right? But the more conservative you make the safety factor the more the profiles begin to look like Deep stop profiles, which, debatably, have been shown not to be safer because you continue to on-gas some compartments doing the deep stop. Again there is a window in conservatism, like going with the flow of traffic, that produces a more safe profile.

If that were true, then there would be zero incidences of people with no underlying preconditions getting bent when following the dive profiles of their computers. We all know that is not true. I have had personal experience of a mild bend in less than 60 feet of water, for less that 50 minutes, but I was working like a dog to recover and refit an anchor. How is this possible if the dive computer models were followed? Because the models and computer do not take into consideration the bodies demand for air/oxygen, due to workload or stress and do not take into consideration additionally inturned inert gas. I don't have the science, I don't have the time or the inclination to look for it either. But I would still rather be safe, be conservative and not fly to the edge on the seat of my pants.

 

[Gary_Ward]

So for new divers my advice is always the same. buy something affordable now that meets your actual and foreseeable needs, because even a little way down the road, your views and tech may change.

But heck, if you can afford a Teric and want one, then I'll happily sell you one of those too

Best Response Award Winner.

Thank you

 

[pauldw]

Once, riding the shuttle bus along the South Rim of the Grand Canyon, the driver was talking about people who like to stand right at the edge of the canyon, play around flapping their arms like a bird while standing on one leg or whatnot, and then get a surprise when a wind gust or a crumbling edge sends them flying. Step back from the edge, and you're a lot safer. The algorithm doesn't matter if you're not diving the edge. Step back from the edge, and use whatever computer you can understand at a glance.

 

[Angelo Farina]

You have made a blanket statement that I don't believe holds up to scrutiny. If I were to follow your advice driving a car on a road, in traffic, with an 80km per hour speed limit then going 79km and hour would be safe but going 40km per hour would be more safe. I believe however that going 40 would make you less safe because your car would be an impediment and would likely get hit by someone going twice as fast as you, going with the flow of traffic in my example is more safe.

This example is not really pertinent, as 80 km/h is not a safety limit, it is a legal limit for not being fined. It was already set much lower, with a proper margin, below the real safety limit, which is perhaps 120 km/h.
Staying on the road, think to the safety distance from the car preceding you: let's say that, for a given speed and road conditions, your car can stop in 80 meters. Keeping 100m is reasonably safe, keeping 120 is even more safe. Keeping 150 is even more safe. And so on... At a certain point, there is no more increase of safety, so increasing it further is pointless, but the safety never REDUCES for staying away from the safety limit...
And here again my engineering training kicks in. It is a problem of optimization. Defining the optimal safety margin should be seen as the compromise between increased safety and increasing costs. For solving an optimization problem, you need to convert the value of additional safety in the same unit as the value of the additional costs. Then you run some optimization algorithm and you find your answer. But it will always be a tradeoff, hence you must respect people who set the optimal point different by your, giving more value to safety and less value to the costs related to making a shorter dive or a longer deco.
In no case a choice which weights more value to safety can result in less safety, it would mean that you are running with a wrong algorithm.

 

[dmaziuk]

If that were true, then there would be zero incidences of people with no underlying preconditions getting bent when following the dive profiles of their computers.

No. Read the DSAT report: the entire 1st chapter is dedicated to explaining why "DCS is not an accident" and how a model that results in consistent 1 DCS hit in 5K dives is better than one that results in a hit "sometimes".

 

[loosenit2]

If that were true, then there would be zero incidences of people with no underlying preconditions getting bent when following the dive profiles of their computers. We all know that is not true. I have had personal experience of a mild bend in less than 60 feet of water, for less that 50 minutes, but I was working like a dog to recover and refit an anchor. How is this possible if the dive computer models were followed? Because the models and computer do not take into consideration the bodies demand for air/oxygen, due to workload or stress and do not take into consideration additionally inturned inert gas. I don't have the science, I don't have the time or the inclination to look for it either. But I would still rather be safe, be conservative and not fly to the edge on the seat of my pants.

You appear to be responding to something I did not say. I did not say conservatism was bad, I said there is a limit to how much conservatism was good.

 

[loosenit2]

This example is not really pertinent, as 80 km/h is not a safety limit, it is a legal limit for not being fined. It was already set much lower, with a proper margin, below the real safety limit, which is perhaps 120 km/h.
Staying on the road, think to the safety distance from the car preceding you: let's say that, for a given speed and road conditions, your car can stop in 80 meters. Keeping 100m is reasonably safe, keeping 120 is even more safe. Keeping 150 is even more safe. And so on... At a certain point, there is no more increase of safety, so increasing it further is pointless, but the safety never REDUCES for staying away from the safety limit...
And here again my engineering training kicks in. It is a problem of optimization. Defining the optimal safety margin should be seen as the compromise between increased safety and increasing costs. For solving an optimization problem, you need to convert the value of additional safety in the same unit as the value of the additional costs. Then you run some optimization algorithm and you find your answer. But it will always be a tradeoff, hence you must respect people who set the optimal point different by your, giving more value to safety and less value to the costs related to making a shorter dive or a longer deco.
In no case a choice which weights more value to safety can result in less safety, it would mean that you are running with a wrong algorithm.

How is it any different that diving limits? NDLs are well below the real safety limit because of conservatism allready in exactly the same way you say speed limits are. They are both probabilistic models. Traffic engineers determine rules based on probability of accidents and then set limits that reflect a level of risk that is acceptable. Decompression (or No Decompression Limits) do exactly the same thing. In fact Bulhmann revised his 16LA to B and C to reduce risk in the same way.

"Staying on the road, think to the safety distance from the car preceding you: let's say that, for a given speed and road conditions, your car can stop in 80 meters. Keeping 100m is reasonably safe, keeping 120 is even more safe. Keeping 150 is even more safe. And so on... At a certain point, there is no more increase of safety, so increasing it further is pointless, but the safety never REDUCES for staying away from the safety limit..."

What you said above is exactly my point. Some conservatism is good, but too much does not help any more and in some cases may actually cause other problems or more risk.

 

[Angelo Farina]

How is it any different that diving limits? NDLs are well below the real safety limit because of conservatism allready in exactly the same way you say speed limits are. They are both probabilistic models. Traffic engineers determine rules based on probability of accidents and then set limits that reflect a level of risk that is acceptable. Decompression (or No Decompression Limits) do exactly the same thing. In fact Bulhmann revised his 16LA to B and C to reduce risk in the same way.

"Some conservatism is good, but too much does not help any more and in some cases may actually cause other problems or more risk.

We agree perfectly on this. There is an optimal amount of safety margin.
Unfortunately I know a number of "tech" diver who choose computers where they can modify these margins to what they call "aggressive" deco plans. Which for me are simply "unsafe" deco plans...
So they spend a lot of money on these advanced computers, just for diving less safely than using cheaper, less tunable basic computers.
I do not see the advantage of doing this...
Instead I appreciate the large, colourful display of these more expensive devices.
I would by happy to pay 199 eur, instead of the 99 eur I paid, for a "super Leonardo" featuring a large, colour display and a wireless data transmission. I do not feel any need of making the deco algorithm less conservative (nor more conservative). It is already "safe enough" for me...