Buoyancy Question

Paleface · Nov 22, 2011

I have a buddy that is diving double steel 95's. He called to tell me he had a bad dive. Said he forgot to turn on he isolator valve on and as he was diving he started to ascend and could not stop until he grabbed the down line,let all the air out of his wing and drysuit, but still was to buoyant.
I guessed he was not weighted properly and he said no all it was is that he breathed up one tank instead of breathing them both down equally. The guys he was diving with also agreed he says.
This doesnt make sense to me, the weight of the air is the same weather it comes out of one or both tanks. If any thing it would roll you,but not send you up. I tried to explain my way of thinking and he blew me off like I have no idea.
Am I missing something here???? Thanks Keith

randy88k5 · Nov 22, 2011

I have never heard that argument before. I have left an isolator valve closed on doubles before, and I did feel a little rolling to one side, but nothing that you couldn't fight against. It did not cause me to ascend uncontrollably. I suspect the person might have been in a position that allowed air to be trapped in a certain section of the wing or drysuit. The air in that section rendered the particular dump point that he was using ineffective.

tyesai · Nov 22, 2011

Paleface:
This doesnt make sense to me, the weight of the air is the same weather it comes out of one or both tanks.

Divers have a way of denying common sense.

Captain12Pk · Nov 22, 2011

Well th easy solution (if your friend was right about the closed isolator) would have been to reach up and open the isolator. Potentially I guess he could have been 7ish lbs heavier on one side than the other, but I can't see the problem you described being the result of a closed isolator. my guess is he had something else going on.

IXÎYÎ£ · Nov 22, 2011

Paleface:
...and he said no all it was is that he breathed up one tank instead of breathing them both down equally. The guys he was diving with also agreed he says.
This doesnt make sense to me, the weight of the air is the same weather it comes out of one or both tanks. If any thing it would roll you,but not send you up. I tried to explain my way of thinking and he blew me off like I have no idea.
Am I missing something here???? Thanks Keith

Nope, you're not missing a thing. Your buddy is wrong. Period. He can prove it easily in a pool by draining one tank with tanks isolated, measuring the buoyancy of the pair and then opening the isolator to allow the tanks to equalize. As you have intuitively - and accurately - surmised, the buoyancy of the twinset won't change a whit.
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tbone1004 · Nov 22, 2011

only thing I could think of is with the isolator closed the left bottle would have been the heavy one and because of that he couldn't vent, but he's full of ****, With it closed he would have had at least half of the volume left, so he was either underweighted or added too much air and couldn't dump. Has nothing to do with the buoyancy of the tanks.

Paleface · Nov 22, 2011

Thanks for the replies!! As he explained more he didnt realize until after the dive when he went to turn off his isolator valve the air rushed into the other tank. When I mentioned that maybe he didnt get all the air out of his drysuit or wing,he assured me that he did when he was holding onto the down line. He dives with no weight and says all the people he dives with that have doubles dont wear lead.
I have 8 dives on my double 100's and I wear 4lbs in fresh,8lbs in salt water. He says I shouldnt need any weight,well I do. I know it depends on your rig and gear but we have a similar set up. I would rather be a little heavy. My last dive I had to pull an anchor and as I was being pulled through the water with the current you get a little light where it is good to have that weight at the end of the dive.
The thing that worries me the most is that he dives with some experienced divers including an instructor. Someone should be giving him some better advice or maybe he is just not asking and drawing his own conclusions. Keith

RonFrank · Nov 22, 2011

Reaching all the valves on doubles should be easy when wearing them.

Dumping air depends on the bladder but also should be easy with practice.

Lots of divers who wear doubles wear weight. This more true if they have doubled AL80s which is more common for new doubles divers.

Your fried sounds like a bit of an idiot. Sounds like he needs to listen more.

Bubbletrubble · Nov 22, 2011

Paleface:
He dives with no weight and says all the people he dives with that have doubles dont wear lead.

That statement says a great deal about your friend.
When determining proper weighting, a diver does not point to someone else and say: "Look, his gear configuration looks the same as mine so I'm going to wear exactly the same amount of lead as he does."

If you want to guarantee proper weighting, an in-water weight check is in order. There is no substitute. This is scuba diving 101. I find it surprising that a person diving doubles (which is a setup more appropriate for a relatively experienced diver) doesn't know this.

Paleface · Nov 22, 2011

Bubble- I truly think he is aware of a weight check and has done so. He has several dives on his doubles and is taking his intro to tech I believe. I dont know what to think about his mind set on this situation.I will talk to him again after Thanksgiving to try and find out more.

Buoyancy Question

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