Negative Entries - A Bad Idea???

[dberry]

It's surprising how much a difference actually sucking the air out of your wing for a hot drop makes compared to just normal venting at the surface to start descent. No extra weight needed. Just be confident you can equalize while dropping that fast.

 

[RainPilot]

Yes, a "negative entry" is probably most often used to really mean "suck all the air from your BC" before you hit the water. That is how we would use it anyway.
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It's surprising how much a difference actually sucking the air out of your wing for a hot drop makes compared to just normal venting at the surface to start descent. No extra weight needed. Just be confident you can equalize while dropping that fast.

How bad is inhaling from BCD/Wing ?

Just an FYI, this thread discusses some of the disadvantages and possible problems associated with inhaling from a BCD, otherwise I agree with DD and dberry.

I believe @tbone1004 is in agreement with myself, I don't ever let gas from my BCD go into my lungs. Ill squeeze out the gas if needed, but with a full tank that 6 pounds is enough to get me going down especially with a giant stride entry.

How bad is inhaling from BCD/Wing ?

 

[REVAN]

I always thought "negative entry" was the way dumpsterdiver used it. Usual entry is inflated BC, do whatever you need to do on the surface, then deflate and drop. "Negative entry" is deflated from splash. I did not think "negative entry" referenced adding more weight than normal.

Although I do think operators tend to overweight divers if its a drift dive -- that is if you let them decide your weight. Last drift dive I did I asked for 12 lbs (with a 3 mm shorty), the operator insisted I use 14 lbs because it was a drift dive. As I wasnt completely sure of my weighting (hadnt been in tropical waters in a while), I gave in and accepted the extra weight. In restrospect I was probably overweighted -- hell 12 lbs is probably a bit heavy,

I was talking with a friend during a hike a couple weeks ago who was telling me about a dive he did in in Africa some years back (probably 10 years ago). The guide gave the divers going on this trek extra weight to get down fast so they didn't blow off the dive site in the current. I'm not sure how much extra that would have been. It was long enough ago, he didn't remember that detail any more. I just thought it all sounded like a bad concept, especially for a tour operation, in spite of a warning that this would be an advanced dive.

For reference, when I'm diving an AL80 and a 3mm shorty, I usually have 6 pounds of lead. If I had 14 pounds, I'd be 8 pounds overweight. That would be pretty close to the 10 pounds I referenced. However, 10 pounds is just an example I picked because it would be enough to get a noticeable downforce from negative buoyancy. If a diver only had 3 or 4 pounds down force, that's not going to be capable of pulling the diver down very quickly; at least not compared to swimming down, which can easily deliver 20 pounds or more of downward directed thrust.

The same as it is not recommended for divers to inflate the BC and use its additional buoyancy to ascend, that recommendation can also extend to not using the BC to descend. I'm thinking, use the lead weights and BC to remain as close to neutral as possible and use thrust to move through the water, whether it be down, up or across.

PS - Good to add the sidebar discussion on the potential hazards of sucking air out of the BC. It would suck to get a pneumonia from the BC bladder.

 

[Storker]

One thing that IME makes negative entries a little complicated, is if you're wearing a (trilam) DS with heavy undergarments. Given the type and amount of undergarments I use, I normally have to hang on the surface at least a minute or three to let the water pressure expel enough air from the undersuit and get that slight squeeze that I need to be able to submerge. If I were weighted enough to be able to just drop and sink, I'd be overweighted by a few kilos. I understand that the situation will be different in a wetsuit.

 

[VR78]

One thing that IME makes negative entries a little complicated, is if you're wearing a (trilam) DS with heavy undergarments.

That. Negative entry with a DS is an exercise in tranquility, especially when there are wet divers in the same RIB. Usually easier to set a rendezvous point near the target depth than to try to chase them going down.

 

[Rusty Roo]

You shouldn't need to add weight for a negative entry.

I've never done a negative entry in a dry suit but imagine it's a pain in the ass (well crotch)

I've sucked air out of by bc for a few years not every dive but i'm still alive. not sure if it's because i throughly clean the inside of my wing after a dive trip.

 

[seeker242]

Never heard of "negative entry" being defined as "overweight yourself". Around here it just means you enter with an empty BC and descend immediately.

 

[dumpsterDiver]

I'm thinking, use the lead weights and BC to remain as close to neutral as possible and use thrust to move through the water, whether it be down, up or across.

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Yes the dive manual will say to remain neutral, but the reality of the matter is that it is less strenuous to allow yourself to become negative (to a reasonable amount) and "glide" (sink actually) down. Freedivers use this technique after they reach a certain depth.. They allow lung compression and possibly wetsuit compression to make them negative and then they get in the resting sink phase. it is a little weird to be holding your breath and just sinking down toward the bottom (when freediving).

Also, if you are wearing a thin wetsuit, your are not going to keep getting heavier and heavier (when scuba diving) If you have a full 7 mm suit and add zero air on descent, you will probably be getting dangerously out of control as you pass 80 or 100 feet. Context is important when you discuss a negative entry.

 

[ReefHound]

These are my thoughts on negative entry diving and why I think it is a bad idea. Am I missing certain applications that would make the negative entry a good idea? I'd like to hear what others have to say on the subject.

Not meaning to pile on but maybe I have a different way to express it. I think your definition of "negative entry" differs from mine and many others. I define it as entering the water negatively buoyant (BC fully deflated) and immediately descending, or at least remaining submerged. As opposed to entering positively buoyant (BC inflated) and returning to the surface prior to final descent. As such, it has nothing to do with "rate of descent" so how fast you can sink versus kick down is irrelevant, or at least a different issue.

Obviously, the risk is that if there is something wrong like your air is not on or major equipment malfunction, it can be more difficult and dangerous to resolve under water. And you cannot see or communicate with those above the water. I wouldn't recommend it to the newer diver or the careless diver.

As for reasons for a negative entry, one is when the surface is rough. I'd much rather hover at 10' or so waiting for my buddy and doing a self-check than bobbing in 3-5' waves. Another is a strong surface current that can whisk you away before your buddy can enter. Another for me as a DM is when I dive bomb with a line to tie off the boat to an underwater structure.

 

[Wookie]

I consider a negative entry to be one with my BCD deflated and not returning to the surface to give an OK when I descent. I will wait at 10 feet or so and wait for my buddy, then we both descend. It does not involve any extra weight than I would normally wear.

I never wear any extra weight unless I'm guiding a dive. Then I use a 2# clip weight from a shoulder D ring in case someone needs it.