Negative Entries - A Bad Idea???

[REVAN]

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

You want to be comfortable doing negative entries, and have some experience diving in currents.

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.

 

[tbone1004]

a negative entry does not require diving an unbalanced rig. An AL80 will have you about 6lbs overweighted due to the gas in the tank. That is enough to make a "hot" descent when you get out of the boat provided your wing is empty. If you start with 10lbs more than you need, that makes you 16lbs negative, and it is highly unlikely that your inflator won't be able to keep up to arrest that descent.

Your comment about the extra lead hurting the drag profile is laughable at best though. 10lbs of weight is nothing compared to the drag of a wing or heaven forbid a jacket bc, and that implies you are basically in a pike diving form going straight down, which you shouldn't be doing anyway.

Not buying recreational divers being able to swim 90-150fpm for any length of time either, not without specialized gear.

 

[northernone]

I agree excessive weighting to sink faster is a bad idea and would possibly have negative consequences. (pun unavoidable )

However, I agree with tbone1004. I regularly do negative entries. For me this simply means diving a neutral for deco rig which by definition must be negative at the beginning of a dive without starting with an inflated BCD at the surface . That sounds exactly like what you suggest as well?

I don't belong at the surface and avoid it as much as possible .

Regards,
Cameron

 

[dumpsterDiver]

a negative entry does not require diving an unbalanced rig. An AL80 will have you about 6lbs overweighted due to the gas in the tank. That is enough to make a "hot" descent when you get out of the boat provided your wing is empty. If you start with 10lbs more than you need, that makes you 16lbs negative, and it is highly unlikely that your inflator won't be able to keep up to arrest that descent.

Your comment about the extra lead hurting the drag profile is laughable at best though. 10lbs of weight is nothing compared to the drag of a wing or heaven forbid a jacket bc, and that implies you are basically in a pike diving form going straight down, which you shouldn't be doing anyway.

Not buying recreational divers being able to swim 90-150fpm for any length of time either, not without specialized gear.

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.

This is inconsistent with normal basic diving guidelines and is clearly less safe than doing otherwise. As was mentioned above, it does NOT imply that excess lead should be carried, over and above what is required to allow a comfortable stop at the end of the dive with empty tank(s).

When making a negative entry, you want to really, really make sure your air is on and your regulator is working, if not, it could become a really big problem really fast, especially if the diver is not carrying ditchable lead, which could turn a potentially fatal accident into an embarrassing incident (i.e., lost weight belt).

I generally try to do all my entries negative, but sometimes I am sloppy about getting all the air from the BC, so a good duck dive, powerful kicking and the avoidance of a full inhalation until you start sinking are effective remedies, unless you have too much air in the BC.

Negative entries are very useful for drift diving when the dive site is deep and the current is strong. Often, we compromise safety for fun or effectiveness or other practical matters. My goal is to be "Safe" but NOT as safe as possible - or i would not have set foot on the boat.

 

[northernone]

I have an experience to share highlighting a bad time I had once with a negative entry. Entirely my own poor pre-dive check however a positive entry would have given me extra time to catch my mistakes.

Rushed dive off a boat, in unfamiliar borrowed gear. BCD inflator tangled behind me out of reach and in my haste hadn't hooked up my drysuit inflator. Dropping rapidly to make the drop in a decent current, suit squeeze getting uncomfortable . Now fumbling with 5mm gloves connecting my drysuit. Thankful for SM tanks since I wouldn't have the flexibility in the crushing suit to reach doubles to find my hoses. In this case sorted myself on the bottom and glad I could equalize on my hot drop as finning up to arrest the decent while decently negative in a squeeze suit could not have been enjoyable.

Take warning .
Cameron

 

[DogDiver]

My gear set up for recreational salt water, techreation salt water and fresh water cave diving hasn't altered in over 10 years. With each of the three different gear configurations, I enter the water, dump the wing, invert and descend head down looking at the bottom. If the visibility doesn't allow me to see the bottom, I follow the anchor line head first.
Haven't had any issues after 51 years of diving.

 

[dumpsterDiver]

If you are wearing a wetsuit, once you get down 30 or more feet, the suit has lost a good bit of lift. If the BC is completely empty and the diver keeps a vertical, streamlined position and the diver avoids completely filling their lungs (and concentrates on full exhalations), a pretty rapid decent can be made without kicking too strenuously. The goal is often to get down pretty quickly, but also without a whole lot of exertion.

If an ear locks up or there is some reason to slow the descent, turning your body flat to a horizontal position presents a tremendous amount of drag and will slow the descent rate considerably, even when 10 lbs negative. It is quicker than trying to add air to the BC, which would be the second step if the problem was not resolved instantly.

 

[Chavodel8en]

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.

 

[Kevrumbo]

Negative head down, hard kicking fast descents can also make it difficult to keep-up with ear equalization as well.

Ideally with a small trained team of three, scooter DPV's are the best tool to use to get down fast in a current without exerting yourselves. In a large group of vacation divers doing manual fast descents however, you might have buddy pairs scattered at different depths in all directions. . .

 

[dumpsterDiver]

I always thought the beginning of this video shows pretty well what a quick, swimming descent looks like. My son is like 13-14 yrs old and is the one kicking down to catch up. We are all probably negative on the descent, but not excessively.

Once you get down far enough to see the target, estimate the current and plan a trajectory, the need for shooting to the bottom is eliminated. Plus on this particular dive, once we got down a ways, it is pretty clear the current is not that strong.