Balanced (DIR) Buoyancy help needed -very technical-

[dumpsterDiver]

Damn I have. 149.. I am an air hog. Blow through most of it in 50 min in 70-95 ft dive

 

[scubadada]

Wow, only on SB could weighting be so complicated. You jump in, you need to sink, you empty your tank, you need to be able to hold your SS at 15 feet and ascend at a reasonable rate to the surface. Ok, you should be able to float your gear if you took it off. The empiric method should help you zero in within a very short period of time.

 

[Usmc0656]

Yeah, that's what I thought too. It sounds easy when you can take stuff with you into the water and just spend some time figuring it out. Not so easy when you don't have existing gear to rent before making your purchase. In this case I needed to have a good understanding of exactly what I need in order to make a decently intelligent purchase of gear that works together for me (type of tank, type of plate, etc). Buoyancy was a huge part of that. Didn't want to drown myself either with too much steel all over the place just because I "think" I might need it. The only thing I can rent from my LDS is the recreational jacket style bcd unfortunately. If not, heck yeah it would be awesome to just put a decent amount of lead on a belt, with my rig or equivalent, and hand off to a buddy a few pounds until I'm neutral at the end of a dive.

 

[Edward3c]

… It comes from lazy instructors not wanting to properly weight their students. Further proof, when we weight students for OWT, they're in AL80's, stab jackets, and usually 5mm wetsuits, and we RARELY put more than 8-10lbs on them, very very rarely will we have an overweight student that needs more *we have rigorous swimming requirements that tend to weed out very out-of-shape/obese students*. If we weighted them for 10% of their body weight, they'd be pinned to the floor.
…

Not so convinced its lazy instructors, although that’s where it starts. Its instructors who haven’t mastered buoyancy themselves, especially if they’ve done the hero to zero [sic] route in nice tropical waters then start teaching in our nice temperate (cool) waters.

Usmc0656
Calculating buoyancy to the Nth degree is fine for an academic exercise. However, in the real world water density changes. Either over time at the same site or as you descend through the water column. For example, two weeks ago we were diving a site with 3m of fresh water over salt. What weighting would you use? Add to that our body’s buoyancy will vary, mine did over Christmas.

 

[boulderjohn]

Not so convinced its lazy instructors, although that’s where it starts. Its instructors who haven’t mastered buoyancy themselves, especially if they’ve done the hero to zero [sic] route in nice tropical waters then start teaching in our nice temperate (cool) waters.

Anyone who knows me knows what I am about to write, because I am on something of a crusade here.

The instructors who don't weight students properly are not lazy, because it does not take any more effort to weight them properly or improperly. A weight check is required by the standards of all agencies I know, so skipping it is a violation of standards. If they are following standards and overweight their students significantly anyway--as most do--it is for a different reason.

A few years ago, I was called upon at the last minute to replace a sick assistant in a course. The instructor in the course said right from the start that he knew I did things differently, but we were going to do it his way (instructing students while they are on their knees); I could just "grit my teeth and put up with it." I did. When it came time to do the weight check, he told me he knew it was a worthless exercise because students needed so much more weight than that, but standards required it. We did the weight check. The students were all very much overweighted, but he did nothing to change it.

Why?

Because students need to be overweighted by a significant amount in order to perform skills while firmly planted on the floor of the pool. If they are properly weighted, they will bob up and down as they kneel, and with their centers of gravity so high, they will tend to tip over. The problem gets worse with PADI's new requirements that students be taught trim as well as proper weighting, so students with weight up high in trim pockets are even more likely to tip over when on their knees. Many instructors have students do the required skills on the OW dives on the knees as well, meaning the overweighting must continue all the way through certification. They will never know what it feels like to be properly weighted.

So it is not laziness--it is a belief that the only way students can learn and demonstrate skill is on the knees, and for that they must be overweighted.

 

[decompression]

Totally agree John, it starts with the IDC, the CD's have to demo what is expected of them and the candidates must replicate it.......surely these CD's would have no issues with proper buoyancy.

Now it's been almost 20 years since I did my PADI IDC and I haven't been exposed to the PADI way for a long time, any recent instructors mind posting on how things are done now?


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[boulderjohn]

Now it's been almost 20 years since I did my PADI IDC and I haven't been exposed to the PADI way for a long time, any recent instructors mind posting on how things are done now?

It varies dramatically from location to location. PADI has publicly stated that it prefers that students be taught while neutrally buoyant and in horizontal trim rather than on the knees. I can assure you that they really do prefer that--I am currently in discussion with headquarters about a future article about it.

They do not require it, though.

Human nature says that if you are allowed to go on doing things the way you have always done it, you will continue to do so unless you see convincing evidence that you should make that change. Unless you actually see what a profound difference it can make in student performance, you are not going to be so convinced. I made the change years ago, but not until after first rejecting the arguments of the tiny few SB instructors who talked about it in the face of the overwhelming majority of posters proclaiming the importance of teaching on the knees. When I made the change, I did not have the courage to do it wholesale. I tried a little at a time until I had reached the point of certitude that students should never be on their knees.

I know someone who recently did his IDC and IE in Roatan, and they made him do everything firmly planted on the knees. They MENTIONED that PADI has officially changed its approach, and they MENTIONED that some day it MIGHT be required, but for now they weren't even going to give it a try. That, after all, would require them to change all their videos of people doing all the skills on the knees.

Early last year I spoke with a PADI Instructor Examiner about this issue. His theory is that the IDC instructors guarantee their students will pass the IE. Over the years they have developed a system for doing the skills that they know will pass. He gave me the sense that if you put all their IDC students in the pool at the same time and told them to do the skill, it would look like a synchronized swimming routine. All you would need is the music. He himself would much prefer to see IE candidates do the skills neutral and buoyant, but many of the IDC instructors are apparently afraid to do it that way because it is not what has been successful in the past.