Misconceptions and Fallacies

[TomP]

Originally Posted by NJMike
I heard many years ago that if you get inside of a garbage (plastic?) bag on the surface, that that would deter shark attacks.

The last I heard they were looking at the garbage bag solution... basically you fill a great big black plastic bag with water and then get in it, keeping any blood or urine confined in it with you, so you neither look nor smell like anything edible. It doesn't "repel" them - they're just not interested.
Rick

A couple of years back I participated in a 'Survival at sea' team building exercise. The basic scenario was you are stranded at sea with only various debris, including trash bags, to aid in your survival. For the reasons listed by Rick as well as for heat retention, hopping into the trash bags was the best way to put them to use. The facilitator went on to say that such use was referred to as a 'Johnson bag'. Take a guess as to what happened next...

 

[roakey]

Since I'm one of the more strident opponents of the BWOD, I figure only Nixon can go to China.

Doesn't mean I think they're a good idea!

Roak

 

[roakey]

Myth #2: Once a cylinder has not gotten a + (plus) rating, it can never get a + rating.

Both are untrue.

Roak

 

[Midnight Star]

'Johnson bag'. Take a guess as to what happened next...

A chorus of ... "Our <blank> has just been eaten!", sung in Soprano F#?

-----

Mike.

 

[plot]

Regarding the trashbags... so if I'm in a vulcanized rubber drysuit... sharks will leave me alone as long as I don't have a pee valve?

 

[charlesml3]

1) Nitrox is something other than air with a different mix. I remember reading one thread here where someone was doing a partial fill with pure O2 and then adding air to reach the proper mix. They then "rolled the tanks" to mix them. Please..... It's just air.

2) One can learn what type of diver another is by posts on Scubaboard.com. Pretty much every discussion here winds up with one post that says "Well, I sure wouldn't get on the dive boat with you..."

 

[Walter]

They then "rolled the tanks" to mix them. Please..... It's just air.

No, it's not just air. The O₂ must be mixed with the air. This is accomplished by shooting the air in at high pressure. Rolling the tanks doesn't mix the air, but it does cool the mixture which results in a more accurate reading.

 

[Blackwood]

Plus, even though you are weightless when properly bouyant, you are still not massless and you are having to push more mass through the water. This may be a small effect, but it's not zero.

That reminds me of a good one:

Myth: When you are neutrally buoyant, you are weightless.

 

[charlesml3]

No, it's not just air. The O₂ must be mixed with the air. This is accomplished by shooting the air in at high pressure. Rolling the tanks doesn't mix the air, but it does cool the mixture which results in a more accurate reading.

That is just absurd. The air is shot in at high pressure because you're pushing it into a pressure vessel. Oxygen and Nitrogen do not have sufficiently different weights such as to stratify in the tank. Fill it slow. Fill it fast. Roll the tanks. It makes NO difference.

I cannot understand why people try to make more of this than it is. Nitrox is AIR with a different ratio of Oxygen and Nitrogen. Air will not stratify in a tank (or anywhere else, for that matter). Nitrox won't either. Why would it?

-Charles

 

[dumpsterDiver]

That is just absurd. The air is shot in at high pressure because you're pushing it into a pressure vessel. Oxygen and Nitrogen do not have sufficiently different weights such as to stratify in the tank. Fill it slow. Fill it fast. Roll the tanks. It makes NO difference.

I cannot understand why people try to make more of this than it is. Nitrox is AIR with a different ratio of Oxygen and Nitrogen. Air will not stratify in a tank (or anywhere else, for that matter). Nitrox won't either. Why would it?

-Charles

This is what I thought until I saw it with my own eyes at the shop. The shop monkey said it only happens on the HP tanks. I would have sworn this was total crap until I saw the readings change with my own eyes