Lookchart67
Registered
How to improved the situation. Can even perform a 5 m safety stop successfully.?
Hit 50Bar becoming uncontrollable positive bouyant problem ..
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Are you diving an Aluminum 80 cylinder? These are known to be positively buoyant as the air in them is depleted. If this is the cylinder you are using then you might need to compensate by either diving with more lead balast so you are properly weighted towards the end of your dive, or if you have adequate weight already then you need to be more proactive in letting air out of your BCD (or wing, depending on your gear configuration).
Remember, as you go up in the water column the air in your BCD/wing is expanding, and the closer to the surface the more it expands (the bubble in your BCD will double in size from 10m to the surface) so if you are not proactive in releasing air, your rate of ascent will increase making it increasingly likely that you will lose control and cork to the surface.
Without knowing more about your gear configuration or what you are experiencing, I recommend some practice sessions in a pool or shallow confined water area, 10m to 15m deep where you can work on fine tuning your buoyancy control. I would also recommend using a similar cylinder that you experienced the problem with, with only 50 to 60 Bar to simulate an end of dive scenario and do a weight check to ensure that you have the correct amount of lead.
If any of the above is not helpful for your specific situation, then please post more details about your gear configuration and what you are experiencing when you dive, so more focused suggestions can be offered.
-Z
Remember, as you go up in the water column the air in your BCD/wing is expanding, and the closer to the surface the more it expands (the bubble in your BCD will double in size from 10m to the surface) so if you are not proactive in releasing air, your rate of ascent will increase making it increasingly likely that you will lose control and cork to the surface.
Without knowing more about your gear configuration or what you are experiencing, I recommend some practice sessions in a pool or shallow confined water area, 10m to 15m deep where you can work on fine tuning your buoyancy control. I would also recommend using a similar cylinder that you experienced the problem with, with only 50 to 60 Bar to simulate an end of dive scenario and do a weight check to ensure that you have the correct amount of lead.
If any of the above is not helpful for your specific situation, then please post more details about your gear configuration and what you are experiencing when you dive, so more focused suggestions can be offered.
-Z
Well, either you need more ballast, or you are not properly venting your bcd on ascent. Is the bcd completely empty at your safety stop? If yes, add a few more pounds on your next dive and check your bcd again at the safety stop. If you still can’t maintain your stop depth with an empty wing, add a few more #s. If you now have air left in the bcd while neutral at 5m, then remove some of the added weight. If you still have air in the bcd at 5m currently, then you are not venting properly on ascent and need to address that first.
What setup are you using now (exposure suit, tank type, how much weight)?
What setup are you using now (exposure suit, tank type, how much weight)?
If bcd is empty, just add some more weight. It is just physics.
ginti
Contributor
If you dive dry, it could also be that you are not purging your dry suit well. But the principle is the same as for the bcd. In summary:
OPTION 1: You need more weight
OPTION 2: You need to eliminate some air (either from the BCD or from your dry suit)
OPTION 1: You need more weight
OPTION 2: You need to eliminate some air (either from the BCD or from your dry suit)
An AL80 cylinder will be negatively buoyant at the beginning of the dive when full, and it will be positively buoyant towards the end of the dive when it is empy-ish.
For example, a Catalina S80 (AL80):
Buoyancy full (207 bar)= -1.6lbs
Buyancy @ 500psi (@ 34 Bar) = +2.8lbs
Buoyancy empty = +4.1lbs
-Z
nomadicdiver
Registered
I believe his point was that aluminum tanks will be buoyant when near empty at the end of the dive. Basically, you have a cork on your back and the lead you carry should account for that transition.
Long, long ago, I taught at a shop that kept steel (still neg on empty) on hand for customers that wanted them and that's all I would dive. More air, less weight belt, less bobbing.
[Edit] But yes, you're right that if the diver consumes 4 pounds of air, they'll be 4 pounds more buoyant regardless of what kind of tank or where that buoyancy resides...
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