Sharing a Dive Computer

[jbtut]

jbtut since you did not provide any parameter if I am diving nitrox and you are diving air you are going to absorb more nitrogen them I will even though you are above me.

Currents do not change the density of water. Depth and time are the main factor on nitrogen absorption you may want to re-read your o/w book and take a class on deep diving or the advance class.


Dive agencies have put in a lot of time and money in to make the sport safe and fun, so they know a lot more about diving then you do. You need to get more diving experience and knowledge before giving advice out on safety.

This is from SDI, Netdoc you may want to re-read the SDI Instructor manual.
Steve, SDI/TDI HQ
Dive Industry Professional
SDI Standards are very clear: Each diver MUST wear a personal dive computer. The ONLY exception noted is a discovery scuba.

Sharing a computer is against just about every industry standard I can think of.

FYI, I just spoke with our V-P Training, Sean Harrison, and after he stopped choking on his inhaled coffee, he confirmed the standards for me. No ambivalence at all.
__________________

Best Regards,
Steve Lewis
Marketing & Communications Director
SDI/TDI/ERDI
steve.lewis@tdisdi.com International Training :: Home :: :: English

I assumed same air mix. If you change that, the other premises fail.

Currents and water temperature DO change density and pressure of water at given locations. However, to be more accurate pressure is the critical variable, not density, although pressure differences are often results of density gradients. Cold water is more dense than warm water. Currents are the result of pressure differences. Just like air flowing around an object creates high and low pressure areas, so do all fluids. Including water. Think about it, if this was not the case, sailboats could not function, you could not swim, fish could not swim etc.

Sure dive agencies spend time and $ researching diving. They may even know more about physics than me. However, all the time and money in the world can't change physics. No matter how hard they try, writing something in a book can't change the physiology of the human body or the physics of fluids.

If you like to blindly follow what some agency recommends without understanding the science behind it, that's fine. Arguing based on agency recommendations is like having a bible verse war with two different religious texts. It's meaningless and no one can win. By blindly relying on a manual you'll probably be safe within their guidelines, so long as the guidelines are safe. However I'd suggest you learn the basic science behind what's happening and make an educated decision. Then we can discuss the science rather than quoting bible verses. If the premises I stated are accurate, the result is accurate. If we add the premise of the same air, is there any other premise that fails or failure in the chain of reasoning?

 

[NCadiver]

1. There's no possible way that a diver who stays at a shallower depth than another diver for an entire dive will take on more nitrogen. (Save for exceedingly unusual circumsances where currents might cause one area of water to be denser than another or something similar)

5. What a particular dive agency says or doesn't say has zero bearing on whether something is safe or not. It may very well be good advice, but physics and physiology determine whether something is safe or not.

I assumed same air mix. If you change that, the other premises fail.

Currents and water temperature DO change density and pressure of water at given locations. However, to be more accurate pressure is the critical variable, not density, although pressure differences are often results of density gradients. Cold water is more dense than warm water. Currents are the result of pressure differences. Just like air flowing around an object creates high and low pressure areas, so do all fluids. Including water. Think about it, if this was not the case, sailboats could not function, you could not swim, fish could not swim etc.

Sure dive agencies spend time and $ researching diving. They may even know more about physics than me. However, all the time and money in the world can't change physics. No matter how hard they try, writing something in a book can't change the physiology of the human body or the physics of fluids.

If you like to blindly follow what some agency recommends without understanding the science behind it, that's fine. Arguing based on agency recommendations is like having a bible verse war with two different religious texts. It's meaningless and no one can win. By blindly relying on a manual you'll probably be safe within their guidelines, so long as the guidelines are safe. However I'd suggest you learn the basic science behind what's happening and make an educated decision. Then we can discuss the science rather than quoting bible verses. If the premises I stated are accurate, the result is accurate. If we add the premise of the same air, is there any other premise that fails or failure in the chain of reasoning?

That not what you said, You said there was no possible way I show you there was. Their are a lot of diver out their were one will be on nitrox and the other will not. And if they are both on nitrox your statement still will not hold up.

What part of physics do current have on nitrogen absorption in the body.

True agency can't change the physiology of the human body or the physics of fluids but they have researched it and came up with best practices for diving with in those parameters.

Where do you think they came up with these recommendations they used the science of physiology of the human body or the physics.

In the end you have not come up and standard for diving or NDL tables for use or publishing.

 

[halocline]

jbtut since you did not provide any parameter if I am diving nitrox and you are diving air you are going to absorb more nitrogen them I will even though you are above me.

Currents do not change the density of water. Depth and time are the main factor on nitrogen absorption you may want to re-read your o/w book and take a class on deep diving or the advance class.


Dive agencies have put in a lot of time and money in to make the sport safe and fun, so they know a lot more about diving then you do. You need to get more diving experience and knowledge before giving advice out on safety.

This is from SDI, Netdoc you may want to re-read the SDI Instructor manual.
Steve, SDI/TDI HQ
Dive Industry Professional
SDI Standards are very clear: Each diver MUST wear a personal dive computer. The ONLY exception noted is a discovery scuba.

Sharing a computer is against just about every industry standard I can think of.

FYI, I just spoke with our V-P Training, Sean Harrison, and after he stopped choking on his inhaled coffee, he confirmed the standards for me. No ambivalence at all.
__________________

Best Regards,
Steve Lewis
Marketing & Communications Director
SDI/TDI/ERDI
steve.lewis@tdisdi.com International Training :: Home :: :: English

I think it's clear from his post that there's an assumption that both divers would be on the same gas. I also think that his point was exactly what you also stated, which is that time/depth is responsible for N2 loading, despite his errant comment about currents. Given the general agreement in your post, I find it a little bizarre that you, as a communications and marketing director for a scuba agency, would reply with as snitty a tone as you did. I don't think it's very professional, to be honest. Leave the snide remarks to us civilians!

These forums are about free and open discussion, which is a fairly strong (and refreshing) contrast to the regimen and sales vibe (education-for-profit-and-increasing-market) that typify the materials of your organization and your competitors in the recreational dive industry.

That said, thank you for participating.

 

[jbtut]

That not what you said, You said there was no possible way I show you there was. Their are a lot of diver out their were one will be on nitrox and the other will not. And if they are both on nitrox your statement still will not hold up.

What part of physics do current have on nitrogen absorption in the body.

True agency can't change the physiology of the human body or the physics of fluids but they have researched it and came up with best practices for diving with in those parameters.

Where do you think they came up with these recommendations they used the science of physiology of the human body or the physics.

In the end you have not come up and standard for diving or NDL tables for use or publishing.

I have not compiled my own NDL tables, have you personally? Even if I had, it makes no difference in this particular discussion. Although I do have a degree in physics I work in another field and I'm not an expert on absorption of nitrogen. However, the basics are fairly simple applications of general physics. More pressure allows a fluid to absorb more gas. Releasing pressure causes offgassing. Just like cracking a beer. Nitrogen happens to be the most common atmospheric gas with a Henry's constant relative to water(and other tissues and fluids in our body) in the range that gives scuba divers problems. It appears from brief research that different tissues absorb nitrogen differently such as fat absorbing nitrogen faster than muscle. However none of that is relevant to the conversation unless you have a dive computer that measures physiological attributes of the diver relevant to nitrogen absorption. All the computer knows is depth, time, and gas mix, and works off some algorithm.

Ultimately, using the same air, a diver who dove a shallower dive would have a more conservative dive profile. That's really the only factor relevant to whether two divers can use a single dive computer safely. (Note that I said "can", not "will"). A relevant response might be "divers don't pay attention and they mess up the plan of keeping the non-computer wearer at shallower depth." (which also happens to be exactly why I said that I would not share a computer).

Quoting agency text lends nothing to the dialogue other than letting us know what the agency thinks. Why an agency has come to that conclusion might be relevant. But you haven't made any attempt to explain that.



As for the water pressure fluid dynamics issue, I'm actually sort of interested to see what the differences are. I don't have any drift dive trips planned and I think it will be easier to measure in a river at higher velocity first. Once it warms up I'll take a more accurate pressure gauge and test around obstructions in a river to see if there is enough difference to measure and if so how much. If there are not significant pressure variations around objects in a river, it's unlikely that there will be in the ocean. But it seems reasonable to me that there might be as much as a 3psi difference and that would be roughly 6 feet difference in adjusted depth readings.

 

[NC Wreck Diver]

Everyone's advice is correct. Rent or buy a second computer. It's a must. The computer updates your exact profile every few seconds, extremely accurately. It is impossible for you and your wife to share this. Speak to your instructor, they will give you sound advice. When you both dive with separate computers, the more conservative one rules. I like to dive with my tables in my BCD pocket, and also a separate timing device too. It's a backup to the computers you will be using.

Safe diving to you both.

 

[halocline]

The computer updates your exact profile every few seconds, extremely accurately.

Sure, but the end result is the application of a theory that has a fairly wide margin for error, and with lots of contributing factors that have nothing to do with dive profile.

Two divers on the same dive could have very different likelihoods of getting DCS depending on physiology, hydration, behavior after the dive, all sorts of things. The computer doesn't know any of this, it just knows your dive profile.

That's why safe diving means staying well away from the mythical border between NDL and required deco, or in dives where you're near that border, doing some optional deco along the lines of what a computer or software or tables would require for dives that enter into deco.

 

[NCadiver]

I think it's clear from his post that there's an assumption that both divers would be on the same gas. I also think that his point was exactly what you also stated, which is that time/depth is responsible for N2 loading, despite his errant comment about currents. Given the general agreement in your post, I find it a little bizarre that you, as a communications and marketing director for a scuba agency, would reply with as snitty a tone as you did. I don't think it's very professional, to be honest. Leave the snide remarks to us civilians!

These forums are about free and open discussion, which is a fairly strong (and refreshing) contrast to the regimen and sales vibe (education-for-profit-and-increasing-market) that typify the materials of your organization and your competitors in the recreational dive industry.

That said, thank you for participating.

No it is not he said "There's no possible way that a diver who stays at a shallower depth than another diver for an entire dive will take on more nitrogen." I add a scenario that change his statement to be false and as long as the divers follow their on table or computer they won't have a problem unlike the several people who have shared computers.

You need to re-read the post I am not communications and marketing director for a scuba agency. I am a diver trying to promote safe and fun diving for all levels of diving.

True these forums are about free and open discussion but bad advice is bad advice and should be point out.

 

[Blackwood]

This thread is far too long and full of piss to read through, but I believe I'm in NetDoc's camp.

If two divers are so far apart that they'll have significantly different inert gas loading, they aren't buddies.

A few feet here is in the noise, especially given the coarse resolution (10 ft) in most dive tables.

I stand corrected! There is an agency that allows sharing a computer. Any others?

Every agency that teaches the use of desktop software for dive planning.

 

[stargost]

This is cool, 12 pages for this subject !
As the op has eventually bought 2 computers, instead of sharing, he should give one to a poor guy who doesn't have one and is forced to share.
Now, main issue, (if I still have followed), the op has bought a suunto and a VEO250, BUT he dives in cold water ... this is BAAAD idea, he should have bought a uwatec one, as it is the only one which incorporate temperature in the algo model and as someone above as stated, it matters.

Oh but hold on, this is not correct, he should keep the gekko, sale the veo, and buy another suunto (at least a D9 to get parity with the uwatec price). Muuuuch better, doesn't matter about about the temperature, but it is good for my Air Liquide stocks, and for poor Finish engineers in general: with Nokia not doing that good in the handset business, they may have to find jobs at suunto. I wonder if you need to be a diver to work there, and how is it to dive in the baltic sea during winter time...

Sorry for the non-sense, couldn't resist

 

[halocline]

You need to re-read the post I am not communications and marketing director for a scuba agency. I am a diver trying to promote safe and fun diving for all levels of diving.

True these forums are about free and open discussion but bad advice is bad advice and should be point out.

I wasn't referring to you, although looking back, your post is the one I quoted. I guess I got confused because the signature at the end of the post was from a guy named Steve Lewis, who identified himself as the Marketing and Communications Director for SDI/TDI etc. If that's not you, and those statements I quoted are not yours, sorry. Maybe you should consider making his quote in your post more obviously a quote, because right now it just looks like your statement and sig.