Negative Entries - A Bad Idea???

[KDAD]

Neutral entry you wouldn't be decending upon entry either. You will still be floating on the surface as you are neutral for that point in the water column and get pushed away from the wreck. Dm says we are going to do a negative entry just means deflate any air from your bc before splashing, could even be when you hit the water, and decend without lingering. If you have to duck dive, great. I don't see anyone running for more weight when he says negative entry.

 

[dberry]

When doing a drift dive to a wreck in a strong current your decent will be at angle. The boat captain will drop you up curent from the wreck so that as you decended you will drift with the current into the wreck. If you don't get down you may very well miss the wreck and float off in the current. At that point you will have to shoot your bouy, get picked up, and hope the captain gives you a second chance.

If you don't do a negative entry and instead linger at the surface the current will take you off of the wreck.

If you can't do a negative entry don't do the dive.

This. I've been instructed to meet up at 30 ft "as soon as possible" after doing backroll entries in Coz, but that was nothing compared to diving a SE Florida wreck in fairly strong current. I'm a newb at this, but I'm still amazed that the Captain could position us so perfectly (un-moored and moving), and that three of us could drop in negative, sink at >99ft/min while moving quite fast horizontally in the current, and still hit spot-on the wheelhouse of the Hydro Atlantic (ca. 130ft) as a group. I know it's "just physics and vector math", but it was still very impressive to me. We did suck the air out of our wings, and especially with doubles there was nothing neutral about the entry The consequences of dawdling on the descent - ending up far down-current of the wreck - would have been painful (as in not diving the wreck.) Obviously the captain and crew were familar with the dive plan. When they said "Dive! Dive! Dive!" they didn't mean "when you feel like it".

 

[dumpsterDiver]

This. I've been instructed to meet up at 30 ft "as soon as possible" after doing backroll entries in Coz, but that was nothing compared to diving a SE Florida wreck in fairly strong current. I'm a newb at this, but I'm still amazed that the Captain could position us so perfectly (un-moored and moving), and that three of us could drop in negative, sink at >99ft/min while moving quite fast horizontally in the current, and still hit spot-on the wheelhouse of the Hydro Atlantic (ca. 130ft) as a group. I know it's "just physics and vector math", but it was still very impressive to me. We did suck the air out of our wings, and especially with doubles there was nothing neutral about the entry The consequences of dawdling on the descent - ending up far down-current of the wreck - would have been painful (as in not diving the wreck.) Obviously the captain and crew were familar with the dive plan. When they said "Dive! Dive! Dive!" they didn't mean "when you feel like it".

Yes the order to "dive, dive, dive" must be followed quickly.

Try hitting a smallish airplane in 185 ft We often drop 0.12 to 0.15 miles south and a little west of our target, sometimes we have currents well over 3 kts at the surface.

I do a back roll, try to straighten out after hitting the water and start kicking! The ability to do a very close to perfectly vertical descent with no visual reference is something that takes some getting used to. I used to hang a pole spear from the band and allow it to dangle and work like a plumb bob to show me which way was straight down. If you don't go vertical, you have a good chance of swimming perpendicular to the current and this will mess up the drop.

 

[REVAN]

I was searching the net for diving speed and stumbled across this instead and thought it was relevant to this thread. It's interesting that dropping weights was not performed or even mentioned in the post accident lessons...

Speed Kills

 

[Dan]

I recently came across a thread about diving in a particular location with currents where a poster stated:



Personally, I think negative entries are a bad idea, and especially when currents are involved. Using excessive weight for downward directed propulsion is going to be either ineffective, or unsafe if it's big enough to be effective. A negative entry seems to invoke too much risk when there are better ways to deal with diving in currents.

My impulse is to caution divers to think about the consequences of negative entries vs. other methods of getting down quickly. My personal preference is to dive with the ideal amount of weight (the minimum needed to be neutral at about 10 feet with an empty tank), and then kick down for a rapid descent if that is what's desired for the dive plan.

An extra 10 pounds of lead will take you down, but if you parachute drop, that 10 pounds is working against the maximum drag profile of the diver moving through the water. You won't descend nearly as fast as a diver who swims down by kicking with an average of 10 pounds thrust and is exposing a minimum cross-section and minimum drag to the water. This level of thrust is easy to produce with decent dive fins. Even a draggy diver should be able to swim in excess of 90 ft/min and a typical recreational scuba diver should be able to easily exceed 150 ft/min. That seems like a fast enough descent to me.

Also undesirable is that any extra weight carried by a diver to do a negative entry will then require the diver to inflate their BCD once down to achieve neutral buoyancy. The extra BCD inflation will then increase the diver's drag in the water making it harder for them to deal with the currents for the duration of the dive.

A diver who uses ideal weighting and swims down will have less drag and be more effective at dealing with the currents during the course of the dive. This diver is also not exposed to the risks of hitting the water negatively weighted and then potentially having to deal with another diver related problem (tank valve not open, regulator failure, BC or DS not connected, etc...) while sinking out of control.

I put the negative entry in the same category as hyperventilating when freediving. It's an idea that has the illusion of making the dive easier, but it really just adds unnecessary risks without delivering a true positive benefit.

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.

You are confusing negative entry with overweighting your gear, I think.

From what I understand, negative entry is simply going down head first, fins up. You use your fins to go down fast in negative entry with no air in BCD. The bad part of negative entry is if you have ear equalization problem. I will constantly equalizing my ears as I go down fast to avoid ear pains at the end of the dive.

Positive entry is going down with head up & fins down. You deflate your BCD air slowly to go down in controlled manner, while equalizing your ear.

You don't want to be overweighted in either negative or positive entry. Conserving as much air as possible for breathing, not for controlling your buoyancy of the overweighted gear.

 

[stuartv]

You are confusing negative entry with overweighting your gear, I think.

From what I understand, negative entry is simply going down head first, fins up..

No. Negative entry means entering the water negatively buoyant. Normally, that just means with an empty BCD. How you choose to descend after you enter the water is a different matter.

 

[tbone1004]

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.

@stuartv the quote above is most accurate spare the halt at 10ft which in my experience is either at 15ft on the hang line for decompression, or doesn't exist due to meeting at the bottom or diving solo.
Negative entry implies immediate descent otherwise you would have entered the water positively buoyant to promote an immediate return to the surface. Why would you have a negative entry and then return to the surface?

 

[stuartv]

@stuartv the quote above is most accurate spare the halt at 10ft which in my experience is either at 15ft on the hang line for decompression, or doesn't exist due to meeting at the bottom or diving solo.
Negative entry implies immediate descent otherwise you would have entered the water positively buoyant to promote an immediate return to the surface. Why would you have a negative entry and then return to the surface?

I understand. I meant whether you go head down/fins up, or if you descend in normal horizontal trim is up to you. I agree that it doesn't make any sense to go in negative if you're coming right back to the surface.

 

[gcarter]

I recently came across a thread about diving in a particular location with currents where a poster stated:



Personally, I think negative entries are a bad idea, and especially when currents are involved. Using excessive weight for downward directed propulsion is going to be either ineffective, or unsafe if it's big enough to be effective. A negative entry seems to invoke too much risk when there are better ways to deal with diving in currents.

My impulse is to caution divers to think about the consequences of negative entries vs. other methods of getting down quickly. My personal preference is to dive with the ideal amount of weight (the minimum needed to be neutral at about 10 feet with an empty tank), and then kick down for a rapid descent if that is what's desired for the dive plan.

An extra 10 pounds of lead will take you down, but if you parachute drop, that 10 pounds is working against the maximum drag profile of the diver moving through the water. You won't descend nearly as fast as a diver who swims down by kicking with an average of 10 pounds thrust and is exposing a minimum cross-section and minimum drag to the water. This level of thrust is easy to produce with decent dive fins. Even a draggy diver should be able to swim in excess of 90 ft/min and a typical recreational scuba diver should be able to easily exceed 150 ft/min. That seems like a fast enough descent to me.

Also undesirable is that any extra weight carried by a diver to do a negative entry will then require the diver to inflate their BCD once down to achieve neutral buoyancy. The extra BCD inflation will then increase the diver's drag in the water making it harder for them to deal with the currents for the duration of the dive.

A diver who uses ideal weighting and swims down will have less drag and be more effective at dealing with the currents during the course of the dive. This diver is also not exposed to the risks of hitting the water negatively weighted and then potentially having to deal with another diver related problem (tank valve not open, regulator failure, BC or DS not connected, etc...) while sinking out of control.

I put the negative entry in the same category as hyperventilating when freediving. It's an idea that has the illusion of making the dive easier, but it really just adds unnecessary risks without delivering a true positive benefit.

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.

I have never seen or heard anyone suggest that doing a negative entry requires the addition of excess weight until you did in this post.

I have done negative entry several times, all without incident, and all with my normal weighting.

There is nothing wrong with negative entry.

 

[gcarter]

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,

But, I've never heard of someone purposefullly overweighing themselves by 10 lbs!!! That's alot of weight and clearly overkill.

I agree that kicking down is a better option.

I confess I have also never heard the suggestion that a drift dive called for extra weight before now And we do a lot of drift diving on the St. Lawrence.

Where does this stuff come from?