Negative Entries - A Bad Idea???

[NW Dive Dawg]

They are simply defining sport diving as less than 40m, less than 40% O2, no deco, and no overhead. Break any of those constraints, it is not sport diving any more.
Or maybe you were trying to make a joke?

No joke. I personally maintain that a dive to 40M on 40% is NOT a good idea and don't care one bit whether it's called "sport diving" or not. That's just my personal opinion and I get to have my opinion. So live with it or feel free to take the alternative.

 

[tursiops]

No joke. I personally maintain that a dive to 40M on 40% is NOT a good idea and don't care one bit whether it's called "sport diving" or not. That's just my personal opinion and I get to have my opinion. So live with it or feel free to take the alternative.

Where does it say that you use 40% to 40m? It only says if you violate either of those it is not sport diving.

 

[NW Dive Dawg]

CMAS says sport diving and recreational diving are the same thing.

2.1.62 “Sport diving” shall mean diving to a depth no greater than 40 meters, using only compressed air or Nitrox (with no more than 40% oxygen) as a breathing gas, never requiring a mandatory decompression stop and having direct vertical access to the surface from which an emergency swimming ascent is possible during an emergency. A synonym for sport diving is “recreational diving”.​

Look......You posted the above and then I simply stated that diving to 40 meters on 40% is a bad idea. According to that CMAS definition above.... a dive to 40 meters on 40% meets the definition of a "Sport Dive". My point was that I think it meets the definition of a "Stupid Dive".

Now on the original subject of negative entries...I think they have their place and time and that adding weight isn't necessary if you're weighted properly. For me personally......properly weighted is about 2lbs more weight than is needed to maintain a safety stop with a low PSI tank.

Just make sure everything is tip top, take nice big exhale and step or roll.......then hold that exhale a bit and then inhale on the descent.

And also make sure you don't accidently have your snorkel in your mouth when you go!

 

[happy-diver]

"Diving to a depth no greater than 40 meters."





















Will some one please separate these two and refer to them independently of each other thanks





















"Only compressed air or Nitrox (with no more than 40% oxygen) as a breathing gas."

 

[Gareth J]

CMAS says sport diving and recreational diving are the same thing.

2.1.62 “Sport diving” shall mean diving to a depth no greater than 40 meters, using only compressed air or Nitrox (with no more than 40% oxygen) as a breathing gas, never requiring a mandatory decompression stop and having direct vertical access to the surface from which an emergency swimming ascent is possible during an emergency. A synonym for sport diving is “recreational diving”.​

If you read the statement.
It says diving to a depth NO GREATER than 40m. Using compressed air OR Nitrox (with NO MORE than 40% oxygen) as a breathing gas.

At no time does it say a dive to 40m using 40% Nitrox.

It does say a 40m dive using air or 27% Nitrox No - stop is within the definition.
It does say a 20m no stop dive on 40% is within the definition.

Interestingly, BSAC doesn't define a recreational dive as being no-stop. A dive requiring decompression is still a recreational dive. Its when you accelerate the stop that it becomes technical i.e. a 40m dive on 27% with an 80% decompression mix.

 

[Eric802]

It’s poorly written. Needs some “or”s and commas.

 

[NothingClever]

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’re over-thinking this.

Negative entries are appropriate and necessary for navigation purposes on a hot drop over a specific objective.

 

[The Chairman]

When you're on a dive boat, they'll also give you limits: Don't go below 120' or stay longer than an hour is common. They obviously don't mean you should dive for 59 minutes at 120'. It's about knowing your limits and how they affect or limit each other. After all, these aren't the only limits you should be considering.

 

[tursiops]

It’s poorly written. Needs some “or”s and commas.

It has a comma....he just missed it.

 

[Alaskan Scuba Dude]

Nothing wrong with doing a negative entry for recreational limits provided depth is limited to your experience.