Negative Entries - A Bad Idea???

[Bob DBF]

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.

I guess that's the point, it is not having extra weight on you to go down faster, it is just not to be buoyant and float to the surface when you hit the water. The control of the drop depends on whether you need to descend faster by kicking down or slower by adding air to the BC. No extra weight necessary.

Although I don't need to do a negative drop where I dive now, I warn the DM and practice a negative drop occasionally when I boat dive.


Bob

 

[ReefHound]

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.

Bad concept as opposed to what alternative, having a bunch of divers lost and scattered on an unfamiliar dive site with strong currents?

As for comparing descent rates from an extra 5 pounds versus kicking, who says it's one or the other? If a fast descent is critical you could carry an extra 5 pounds AND kick down. But once again, negative entry is not about rate of descent but about immediate descent without popping back to surface after entry.

 

[ReefHound]

Although I don't need to do a negative drop where I dive now, I warn the DM and practice a negative drop occasionally when I boat dive.

As a working boat DM, I really appreciate a heads up when a diver plans to do that. You never know what is happening below the surface but it's nice to know anytime a diver intends to deviate from the norm. When we just said in the briefing to give us an ok and wait for your buddy on the surface sideline and a diver that looks like he just woke up with a hangover jumps and disappears, you wonder. Is he overweighted and plummeting helplessly to the bottom? Did he not listen to the briefing and if not what other key info did he miss? Does he just think procedures are for the common folk and he's a prince?

 

[Wookie]

As a working boat DM, I really appreciate a heads up when a diver plans to do that. You never know what is happening below the surface but it's nice to know anytime a diver intends to deviate from the norm. When we just said in the briefing to give us an ok and wait for your buddy on the surface sideline and a diver that looks like he just woke up with a hangover jumps and disappears, you wonder. Is he overweighted and plummeting helplessly to the bottom? Did he not listen to the briefing and if not what other key info did he miss? Does he just think procedures are for the common folk and he's a prince?

Be careful. You're sounding like Mel.

Hhahahahahahahahahahahahahah!!!!!!

 

[stuartv]

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

I'm not sure if you really "get" what tbone said earlier.

If you are diving with an AL80 and are perfectly weighted, then you will be neutral with an empty tank and an empty BC. A full AL80 will be 6# more negatively buoyant than an empty one. So, with perfect weighting and a full AL80, you will be 6# negative at the start anyway, without carrying any "extra" weight. If you're diving a 100 or 120, you'll be even more negative at the start - 8 - 9#.

If you are properly weighted, you should be able to drop in with an empty BC and get right down with no trouble. If you are only 3 or 4 pounds negative, you're either diving an AL40, an AL80 that is only half full, or you are not carrying enough weight.

 

[archer1960]

I've only done one negative entry (on the wreck in Coz last fall, with lots of current that day), but there was no extra weight added, just squeeze almost all the air out of the BC, and don't resurface after entering the water. With no air in the BC, I sink fairly fast with a full tank. By the end of the dive, I"m pretty near neutral at 15' for the safety stop, though that day, it didn't matter since we were hand-over-handing up the mooring ball line like flags in the wind.

 

[dumpsterDiver]

As a working boat DM, I really appreciate a heads up when a diver plans to do that. You never know what is happening below the surface but it's nice to know anytime a diver intends to deviate from the norm. When we just said in the briefing to give us an ok and wait for your buddy on the surface sideline and a diver that looks like he just woke up with a hangover jumps and disappears, you wonder. Is he overweighted and plummeting helplessly to the bottom? Did he not listen to the briefing and if not what other key info did he miss? Does he just think procedures are for the common folk and he's a prince?

Lol. I had a DM all pissed and he chewed me out when I got on the boat. I was actually surprised at his intensity,. All I could say was that my perfectly executed duck dive was intended to signal to him that I was OK and intent on descending. As I recall, my explanation did little to ameliorate the situation. Charter boat in the keys.

 

[dmaziuk]

cue in the recent A&I thread on Roatan accident. Though she did apparently put the gear on in the water so that wasn't quite what's being discussed here.

 

[Gareth J]

I think the OP demonstrated a lack of knowledge and understanding of what a negitive entry is and why it's used. A demonstration of the difference between internet diving and real world experience.

There are many skills and techniques that may appear dangerous or risky, if you don't fully understand the process and reason. Often, techniques are developed to minimise risk and danger in particular environments or to solve particular problems.

Gareth

 

[100days-a-year]

Not sure I like all this negative talk.