Misconceptions and Fallacies

[Walter]

The assumption that one or the other is a fallacy is a fallacy in itself.

My belief is that in the case of "nitrox makes you feel better" that the diver has been experiencing sub-clinical DCS and that the lower N2 content of nitrox improves how they feel.

If, OTOH, the dives were shorter, or the diver had a better ascent and stop procedure, then he would not experience sub-clinical DCS on air and wouldn't see an improvement when going to nitrox.

I used to see a difference in fatigue level with nitrox when I first started diving. After starting to do deep stops the difference disappeared.

Like a lot of decompression questions, there's no guarantee that the above interpretation is correct, but it consistent with what I know about decompression.

There is no evidence that fatigue is a symptom of subclinical DCS. Diving with nitrox does make some people feel better than diving with air, but give them air, tell them it's nitrox and that'll make them feel just as wonderful.

 

[Codyjp]

being overweighted means that your BC is bigger, bigger BC=more drag. More drag=more air... probably a negligible aruement though.

 

[MikeFerrara]

Yeah. When people talk about divers going around feet down at a 45 degree angle finning heavily just to keep depth, they normally refer to them as "overweighted", when in reality the true problem is that they don't have enough air in their BCD to be neutral. They may or may not be overweighted.

There's more to it.

I agree that the probelem isn't necessarily that they are over weighted but they are almost certainly out of balance and therefor can't get trimmed. The center of buoyancy is above their center of gravity...ie the top half wants to go up and their bottom half wants to go down. If they are foot heavy, which is common because many have most of their weights below the bc bladder, they must be negative in order to swim forward without also swimming up (due to the foot down attitude). The end result is not only that they swim in a head up trim but since they are negative they either have to inflate or keep kicking when they stop. The answer is to get those centers in the same place and due away with those apposing forces.

The assumption that the problem comes from being overweighted comes from the fact that if you are neutral, you don't beed any air in your bc and your bs won't be more buoyant than the rest of you. In the tropics where you don't need mych exposure protection that will compress with depth, it's pretty close to being true in most recreational gear. If you don't have any air in the BC, you don't have to worry about it making your top half buoyanct.

 

[lifeisfullofgooddives]

How about the myth.... that I won't throw you overboard for throwing your mask in my camera bucket..

 

[Gary D.]

One of my favorites Misconceptions and Fallacies

"The water that is trapped between you and your wetsuit is what keeps you warm."

Everyone knows it not the water, it's the pee.

Gary D.

 

[Gary D.]

Just because you caught it in the ocean, doesnt mean it's safe to eat.

It could be one of those Brown Trout from the Butt Dump they're talking about.

Gary D.

 

[MikeFerrara]

There is no evidence that fatigue is a symptom of subclinical DCS. Diving with nitrox does make some people feel better than diving with air, but give them air, tell them it's nitrox and that'll make them feel just as wonderful.

Fatigue is a symptom of DCS. I suppose that would make it clinical DCS though.

Back when I had heavy teaching schedules I experienced extreme fatigue and some nasty aches more than once that were atypical enough that I'm pretty sure (after the fact) that I was mildly bent...but bent, even though, my computer/tables were plenty happy.

Surfacing with less of an inert gas load is what solved the problem. Using nitrox and/or appropriate ascent gasses are sometimes part of that but so are ascent stratagies that I knew nothing about when I first noticed the problem.

My experiences aren't what you would call evidence like a peer reviewed studdy but I felt bad enough for long enough after enough diving weekends that I had to make it go away anyhow. I did. The bottom line is that you need to find the gas/ascent procedure conbinations that work for YOUR BODY for the dives that you're doing.

 

[The Kraken]

Misconception:
"Being overweighted automatically increases air consumption."

The fact is that if your buoyancy control is good, being overweighted has a zero or negligible impact.

Mike,

This is one with which I must disagree with you. Buoyancy and mass are two different things. You can be neutrally buoyant with a 2000 pound anchor attached to you, but try moving that thing. Takes quite a bit of effort.
It's no different than having 50 pounds of lead on you. You may be neutrally buoyant, but you have to make that mass move and you have to stop it. It takes more energy (ie more calories which require more oxygen) to move 2000 pounds than it does 10 pounds.

The laws of inertia at rest and at motion . . . and so forth . . .

the K

 

[heliflyer]

How about the myth.... that I won't throw you overboard for throwing your mask in my camera bucket..

:no

 

[del_mo]

One of my favorites Misconceptions and Fallacies

"The water that is trapped between you and your wetsuit is what keeps you warm."

Is this a trick?

http://www.cavediggers.com/Main_Page/Articles/Wetsuits/wetsuits.html