LowVizWiz:
1. If you are not "flying" your computer waiting for it to tell you when it's time to go up wouldn't you know before hand what your NDL is?
No. A lot of people doing multi-level reef dives don't know exactly what depth they'll hit max., or on average, though they likely have a max. depth in mind, and dive till they run low on gas, NDL or things to see, or get cold or bored.
2. If you feel it is an unnecessary reduction and you have the gas to extend the dive what is stoping you?
If you violate your computer's NDL, you go into deco. The large majority of rec. divers aren't deco. training, and aren't advised to deliberately go into deco. with just a plan to ride a computer. And on a charter, if you get caught going into deco., they might just sit you out for the day from what I understand.
This illustrates my point perfectly, If you know those differences going into the dive and have plenty of gas to complete the dive:
Is the only factor stopping the diver the brand of computer they have on their wrist?
Would having a computer that said it's okay to stay another 12 minutes or less (Not 17 minutes
) make it all of the sudden ok to complete it?
They don't know the exact differences going into the water, and based on others' reports, issues like rate of ascent and surface interval impact the NDLs in a way that most divers on a boat can't predict in advance. So you can't just say an Oceanic gives x more bottom time than a Suunto. Therefore, you can't plan precisely in advance.
Yes, having the computer that says another 12 minutes is okay makes it okay, at least for most, since that's a model that works well in the real world (where a lot of people dive Oceanics), and it doesn't put you in deco., lock you out, or trigger boat staff to bench you for the day.
My point is people aren't planning their dives and diving their plans, rather they want to strap on a computer and jump in the water. Once they are at the bottom and find out they have different BTs they do not know what to do.
It's much easier to blame the gear than address the lack of knowledge.
Diving to near NDL, or low gas, a given turn pressure, a duration (e.g.: 1 hour dive) or 'Eh, I've had enough' may just be the plan, and adequate for some common recreational diving.
Let's take live-aboard example. You may not know exactly what site conditions will make optimal, or just how deep you'll decide to go, and if the captain says be back in an hour, you may not want to be back in 55 minutes.
Yes, a person with enough knowledge and seasoned experience could work around the issue of mixed computer diving, but it's easier to avoid bring a more conservative computer into the mix. More practical for a low of divers.
And for the diving a lot of people do, it works fine.
Rather, I intended to compare actual bottom times allowed between a well-liked computer and one that isn't.
I see your point. From what I'm told, technical divers are not likely to 'ride' their computers' NDL output on loosely structured exploration dives on coral reefs, and can set their Petrel to the kind of dive they intend to do (assuming they're not running it in gauge mode and diving tables cut with VPlanner maybe?). Most Suunto owners are doing rec. dives, trust the computer's advice on NDL, and make out fine doing it that way. It's just than an Oceanic offers more bottom time via a liberal algorithm and people also seem to make out fine with that.
I'm not saying Oceanics are 'better' than Suunto, since there are more factors that weigh into the desirability of a given computer. But all other things being equal, I think most divers would consider more bottom time better than less, if people diving with 'more' in wide-spread real world diving aren't getting bent more.
Richard.
