Buoyancy Change Mystery… #askmark @ScubaDiverMagazine


Buoyancy Change Mystery… #askmark @scubadivermag
Dreoni
@dreoni_
#AskMark Hi Mark! I got a mystery for you. I was diving properly weighted in the morning dive but then on the next dive I needed 2 extra Kgs and I was still a bit floaty at the end with a fully deflated bcd. In the 2h between the dives I ate, went to the WC and my semidry dried a bit. The tank was the same capacity but a different one (both 15L steel). I ended both dives at 50bar. I had a bit of water in my BCD. My buddy did not change its weight and was fine. So It's something to do with me/my equipment. I counted the lead afterwards and indeed I had 2 extra Kgs. I asked around the dive shop and I got: water in my bc, different tank weights or air pocket in my semidry. Any other ideas on what could have made such a drastic difference?

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David123p51
David123p51
7 months ago

Eating won’t change your buoyancy “that much” challenge accepted!!

rvanderhulst86
rvanderhulst86
8 months ago

I could indeed see some air in the semi-dry as an issue (I always need to be sure to burp my wet suit before going in to the water, otherwise I will have issues getting down the first time but at around 5 m I will release the excess air and the problem is fixed). Also a buddy of mine has two 12 L steel cylinders and needs about 2 kg extra weight for one of the two, otherwise he also can’t get down

Amadeuss
Amadeuss
9 months ago

Ambient temp and wetsuit.
The hotter it gets it will get mote buoyancy. I bet he could remove those 2kg 20min into the dive when suit cooled down.

hady morad
hady morad
9 months ago

#askmark here’s one for you. i dive to 55 meters on air on a regular basis (i’m technically trained). one time i was diving to said depth and everything was fine until i passed 50 meters. out of nowhere i went into full on panic mode for no reason what so ever. i ascended to 45 meters and i was fine so i stayed there for a couple of minutes then tried to go back down to 55 but i panicked again so i called the dive, did my deco (with 50% and 100%), and got out. my buddy at the time told me that i need helium in order for that not to happen again. i honestly don’t know what happened or why so i’d love your input on that

Scuba Diver Magazine
Scuba Diver Magazine
Reply to  hady morad
9 months ago

My first thoughts are nitrogen narcosis as the effects seem to be pressure related. Down at 50m your partial pressure of N2 is 4.74 which is well above where many divers feel the effects or nitrogen narcosis. That increase in Nitrogen that’s absorbing into your blood changes the chemical balance and can have a range of effects on your brain’s chemistry.

Adding helium to your breathing gas would help as it would dilute the N2 and O2 in your gas mix, which is already getting close to dangerous levels at 55m

hady morad
hady morad
Reply to  hady morad
9 months ago

@Scuba Diver Magazine yeah that’s the thing. i was always able to manage the narcotic effect at that depth even if i descend faster than usual. this time i couldn’t. i think carbon dioxide buildup could could be added to the equation because the dive was from a zodiac and i was hooking everything up while battling chops on said zodiac (which was a bit of labor). i was thinking maybe some carbon dioxide plus slightly faster descent rate was the reason i got that narked. what do you think? thanks!

Rob Wesler
Rob Wesler
9 months ago

#askmark Question regarding refs…my girlfriend has asthma and while she has been cleared to dive to several doctors, she is extremely sensitive to breath ability on refs, particularly when we get to 60+ feet (she is PADI AOW). Price is not really a concern, so we are looking for the best breathing reg- any suggestions would be welcomed. Love your posts! Rob

Scuba Diver Magazine
Scuba Diver Magazine
Reply to  Rob Wesler
9 months ago

I’d look for a balanced or overbalanced 1st stage with high airflow and breathing adjustment. Something like the Scubapro Mk25EVO or Mares regulators with the VAD+ system have great airflow.

Regulators with a nice breathe that spring to mind are the XDEEP NX700 (but they’ve had recalls recently), Atomic Regulators are always a good choice, Scubapro A700 or the D420

Robert Elzey
Robert Elzey
9 months ago

#askmark I live in the USA. This winter I bought 120 HP steel tanks. They are heavier then the 80’s I’ve been diving with. I’m 6’ 4” 265 lbs. With this new set up in freshwater I’m 7 lbs negative without adding any lead. If I add a 3 mm it makes it neutral with out adding any lead. On dives that I don’t wear a 3 mm or more. Any suggestions that I could do to make me more buoyant without having to add more air in my BCD.
Thank you
Rob Elzey

Kilbofragins
Kilbofragins
9 months ago

What about breathing issues, if you struggle a bit and take more air into the lungs it can exaggerate the issue, so you end up fighting it the whole dive, especially if you’re a relatively new diver.

Bill Thomas
Bill Thomas
9 months ago

Were both dives to the same depth?

McrsftHater
McrsftHater
9 months ago

Hi Mark! I dove with one guy about the average body shape and he put 12 kg of lead on himself. I told him that it’s probably too much but he replied that he tried to put less and couldn’t get underwater. How it that possible?

Ricky
Ricky
9 months ago

Love the music. So suspenseful

Tim Gosling
Tim Gosling
10 months ago

My bet is the change of cylinder. I have a pair of 12.2 litre Fabers that are half a kilo different but it can be more extreme. I have data on 15 litre Fabers that range from 16kg to 18.4kg.

DTT
DTT
10 months ago

the worst time i had with buoyancy was on a liveaboard in the red sea. i now think it was because i was wearing a vest under my 3mm. i think it was trapping air and caused all sorts of issues. i’ve never had that problem before or since. why i didn’t take the vest off and try it i’ll never know

Timo Buhmann
Timo Buhmann
10 months ago

Sure you can have a 2kg change by steel cylinders. I have two cylinders 12 liter steel long from two manufactures. One is 13.3kg and on is 15.5kg. On a 15 liter cylinders ranging between 13-16kg is not of any wonders. Checking the weight marking on a cylinder is always a good idea.

adam211086
adam211086
10 months ago

The person doesnt state their dive experience. A diver with limited experience may not notice their breathing has changed. 1st dive they may have been more relaxed and holding a lower lung volume, 2nd dive maybe holding a higher lung volume, that alone could account for 1kg+ add in some air trapped in the semi dry 0.5kg and a different 15kg cylinder could give another 0.5kg swing you have your 2kg difference.

Dreoni
Dreoni
10 months ago

Indeed! I think it was a combination of trapped air and a change of the cylinder (one seemed older than the other). Now I always make sure to properly “burp” my semidry just in case! Thanks for the answer!

Joseph dracula
Joseph dracula
10 months ago

🧐👍🇵🇭🤿! Interesting.

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