Night Dive Unwanted Ascent

[greg454]

This is ironic, I did a 90 ft night dive with no problems whatsoever, but on the second dive 30 ft reef dive I got into trouble.

My mask got full of water, so I did the clearing technique, head up, blow air through the nose. Only thing was that instead of moving just my head up, I moved the entire body up. And although my BCD was deflated, I started to ascend, but because it was dark and I was concentrating on clearning my mask, I didn't notice. By the time I was done, I was on the surface. I tried going back down but coudn't, I don't know if it was my nerves. Luckily, some people also came up and we swam together to the boat.

Aparently, I wasn't the only one who got disoriented. It was embarasing nevertheless. Does it make sense to fail at 30 ft if you did so well at 90 ft? Is it some kind of murphy's law? The dive you think is easy is the one that gets you?

 

[Henryville]

It does make sense, and you could probably explain it with simple physics. Remember when you were studying to get certified, and you compared how the volume of gas changed going from one depth to the next? Take a look at how much it changes going from 90 feet to 80 versus 30 feet to 25. Even if you had just a little gas in your BC, and you were neutral when you began clearing your mask, you would get a fairly rapid buoyancy change even moving up just a few feet.

Add to that - I am assuming you were in a wetsuit - that there is a tipping point for expansion of the neoprene somewhere in that shallow range, and you can add that to the equation. The difference in neoprene crush and therefore buoyancy swing from the suit going from 90 feet to 80 is virtually nil.

What you really should have learned is that you, like most newer (and plenty of long-time) divers, rely on a visual reference to control your buoyancy. If you were truly neutrally buoyant, you would likely not have experienced much of a change in depth - maybe a little if you took an extra-deep breath to get the mask cleared, but then the clearing would have counter-acted that.

Keep diving and pay attention to this by every once in a while "freezing" and observing whether you're sinking or floating up. Awareness is a big key to proficient buoyancy control.

Have fun, and keep thinking! Good question.

 

[Whale Whisperer]

I think the biggest factor here was your mask flood and the fact that you were in the middle of a night dive. When your mask is flooded you can't see anything, so there's no reference for you to look at anywhere around you ESPECIALLY at night. This makes a major difference and this is why you perform your mask flood on a stable and safe area during your open water training, also most people change their breathing patterns during situations like this, so alot of times when there are situations like: Mask Flood, and share air situations alot of new people will go right to the surface so it takes some practice.

I think if you didn't have the mask issue you would have been just fine. If your BCD was totally empty like you said, how much air did you have in your tank? If you had more than 500psi, you may have been underweighted, and I highly recommend that you perform a Buoyance check the next time you get a chance

 

[DandyDon]

I like to carry a couple more pounds of lead on the shallow dives than the deeper ones to help control buoynacy. I have a question, tho...

Luckily, some people also came up and we swam together to the boat.

Where was your buddy? A newby on a night dive needs a buddy who sticks very close.

 

[jbd]

No need to raise your head to clear your mask. Doing so will typically result in changing the attitude of your body i.e. the upper body raises along with the BC. Even a small decrease in ambient pressure will automatically create a state of positive bouyancy. Without macro visual reference, most divers will ascend unchecked. Learn to cue on the micro visual references and also learn to feel what your ears are telling you.

As noted by Henryville above, practice being motionless and controlling your depth while doing mask and regulator skills.

Again reinforcing what Henryville said above, the greatest volume changes occur in the range from 33 ft to the surface. The volume changes at 90 feet are much smaller.

 

[krazyman]

When clearing mask, some tend to take deeper breathe and exhaling thru nose slowly and hence increasing one's bouyancy. Without visual reference, one may ascend below knowing it.

 

[ScottB]

I like to carry a couple more pounds of lead on the shallow dives than the deeper ones to help control buoynacy.

:huh:

Wouldn't carrying more lead then necessary make it harder to control buoyancy?

You would need more air in your BC to compensate for the increased amount of lead. With more air volume in your bc, the change in bouyancy from it's expansion on ascent or compression on descent would be greater.

Take care,

 

[spectrum]

IMO you need enough weight to make a controlled ascent or enjoy the shallows on on a near mepty tank without gross reliance on lung volume. Every diver need to make this final transition in the dive and grabbing the anchor line does not count.

The fact that the OP unknowingly began an ascent and subsequently corked with an empty BC tells me he was underweighted. The fact that it started as he puffed up to clear his mask just set it off. If he had any neoprene to speak of it would have overtaken him after we ascended a little anyway.

You need what weight you need to offset your worst case bouyancy during a dive. For those other moments that's why you have a Buoyancy Compensator. Sure having a little more air to it adds to volatility but if it's not excessive it is entirely managable as is the entire dive profile. The correct weight for the diver and gear is not an evil thing.

Pete

 

[marusso]

It does make sense, and you could probably explain it with simple physics. Remember when you were studying to get certified, and you compared how the volume of gas changed going from one depth to the next? Take a look at how much it changes going from 90 feet to 80 versus 30 feet to 25. Even if you had just a little gas in your BC, and you were neutral when you began clearing your mask, you would get a fairly rapid buoyancy change even moving up just a few feet.

Add to that - I am assuming you were in a wetsuit - that there is a tipping point for expansion of the neoprene somewhere in that shallow range, and you can add that to the equation. The difference in neoprene crush and therefore buoyancy swing from the suit going from 90 feet to 80 is virtually nil.

What you really should have learned is that you, like most newer (and plenty of long-time) divers, rely on a visual reference to control your buoyancy. If you were truly neutrally buoyant, you would likely not have experienced much of a change in depth - maybe a little if you took an extra-deep breath to get the mask cleared, but then the clearing would have counter-acted that.

Keep diving and pay attention to this by every once in a while "freezing" and observing whether you're sinking or floating up. Awareness is a big key to proficient buoyancy control.

Have fun, and keep thinking! Good question.

Great advice as always Dev. When are you coming back down to HH?

-Michael

 

[TrickyRicky]

After awhile you'll get really familiar with your equipment and you'll be able to get your hand on your quick dump valve to help recover from a unwanted rapid decent. I've run into similar situations where multitasking and unfamilar equipment has led to chaos. Fortunately I've learned from my mistakes and practiced different drills with my gear. So far, So good! I've still have a lot to learn. Have Fun!

Rich