Question regarding neutral buoyancy

[scubaozy]

I don't use a bar, but I think that they can be used for momentary stabilizing. If a student never let's go, that's an issue in my view. However, they are likely not applying as much weight on the bar as they would with fin tips for the simple reason that people are typically foot heavy.

I think you are referring to "fin pivot" that exercise do not exist anymore, no requirement for pivoting with fin tips.

Still needs to go. Have students hold one wrist with the other hand. If you distribute weight properly, they are not sculling with their fins.

Buddha does not exist either, it is called hovering, no requirement to hold that position. Only the picture in owd manual depicts it. I have a feeling you are fighting ghosts.

I disagree on both points. Yes, if a student isn't perfectly horizontal, they will continue to ascend slowly as they swim forward. Except they can make adjustments by correcting their trim, exhaling completely, etc.

I don't think that students comfortable in the water start breathing erratically. Keyword is comfortable. There are a number of things I do prior to having students in scuba, including a modificaiton of some mask/snorkel skills taught to me by @Peter Guy.

My recommendation is directly to OP based on the input. OP understands and could get to NB but loses control and cannot explain why. OPs instructor advise OP to set lightly negative and compensate with swimming/kicking. To me this looks like there could be a problem in the swimming technique. You need an event to put you off from NB, e.g. erratic breathing (lack of breath control) or wrong swimming technique. Anyone guess could be better than mine or yours, as this is a of remote diagnostics based on statements, so, suit your self if you disagree.

 

[wetb4igetinthewater]

I think you are referring to "fin pivot" that exercise do not exist anymore, no requirement for pivoting with fin tips.

Didn't say there was. Still being used.

Buddha does not exist either, it is called hovering, no requirement to hold that position. Only the picture in owd manual depicts it. I have a feeling you are fighting ghosts.

Still being used.

My recommendation is directly to OP based on the input. OP understands and could get to NB but loses control and cannot explain why. OPs instructor advise OP to set lightly negative and compensate with swimming/kicking. To me this looks like there could be a problem in the swimming technique. You need an event to put you off from NB, e.g. erratic breathing (lack of breath control) or wrong swimming technique. Anyone guess could be better than mine or yours, as this is a of remote diagnostics based on statements, so, suit your self if you disagree.

The OP received a recommendation to add weight. Someone explained the physics of why that is a bad idea. There is general consensus of which I'm a part that is a bad idea, so suit yourself if you disagree.

 

[scubaozy]

This part makes me worry about your instructors. Some kind of weight check is essential, otherwise you have no idea how much you might be overweighted. Yes, if you're badly underweight you can't descend, but presumably everyone figures this out on their own and it does not cause a problem except having to exit the water and get more weight.

And the instructor should never give you what they think is proper weighting, unless you're in a new exposure suit or other big change in gear, and in that case they should be asking you what you had before and then modifying it. You tell them, not the other way around.

I agree that some very basics have been neglected. Every time a SI messes up another instructor somewhere else in the planet is crying, having to fix prior errors. Having said that, students as well need to take responsibility of their own learning. Performance requirements are in the OWD manual, they can always discuss them with their instructors. At the end the students are buying a service, its their right to expect and demand quality.

 

[scubaozy]

Didn't say there was. Still being used.

As long as no standards are violated, instructors can choose and adapt how they teach. There is no scuba police.

The OP received a recommendation to add weight. Someone explained the physics of why that is a bad idea. There is general consensus of which I'm a part that is a bad idea, so suit yourself if you disagree.

I just copied and pasted the most part of the original post:
"
After establishing neutral buoyancy, your body still ascends or descends as you inhale or exhale. Maybe I inhaled too much or at the wrong moment, I started to ascend more than I would like and it became difficult to bring myself down again. This happened a few times during my dives and I had to pull the exhaust valve quickly to prevent myself from continuing to ascent.

Afterwards I asked my instructor that to avoid this problem, if it's better to remain slightly negative buoyant. With slightly negative buoyancy, you can be neutral when you inhale. When you exhale, you will descend but you can easily control it by kicking. And you don't need to worry about accidental ascending anymore. My instructor said it's ok.
"

 

[wetb4igetinthewater]

As long as no standards are violated, instructors can choose and adapt how they teach. There is no scuba police.
"

The fin pivot is a poor teaching tool in which a student is foot heavy and negatively buoyant. There is no reason to cling to antiquated methods when better methods are available. It just hampers new divers’ progress. Same is true for teaching on the knees. If open water divers were taught properly, GUE fundies may never have been created.

 

[Coztick]

I think the fin pivot could be modified to dial in trim right from the beginning.
Have the students due the typical fin pivot while holding 3lbs in each hand.
When they have enough gas in their BC and are rising off the bottom, have them extend their arms up until the fin tips leave the bottom. Let them find perfect trim through subtle weight shifts.
Until they can hang motionless, they may never truly get how easy diving is.
Trim is like balance. Without it, everything is harder.

Cheers

 

[Blackcrusader]

Scuba Police are everywhere nowadays I'm surprised there isn't a certificate for it. No idea what this instructor was teaching in this class... it could have been a peak buoyancy class but guess away....

 

[inquis]

I never really understood the on the surface weight check.

On a pragmatic note, there's often easier/quicker access to weights on the surface. If done at the beginning of the dive*, it will ensure the ability to stay down if necessary. Along those lines, it prevents "corking" on the way to the surface from the SS due to thicker wetsuit expansion. Corking isn't really an issue in a 3mm suit or less, but thicker suits can be surprisingly expansive in that last 15 ft.

(*) Check/adjust at the beginning of the dive by leaving off about 4-5 lb (~2 kg) from what you think you need to simulate having breathed your tank to reserve pressure (assuming an AL80). Once you've gotten neutral at the surface, then add that remaining weight, and you're good to go. (Make sure your wetsuit is flooded when doing it this way.)

 

[napDiver]

@inquisitAhh I see... it's literally an on the surface buoyancy is roughly not too buoyant at the end of the dive. The removing the corresponding weight to simulate an empty tank makes a lot of sense, I've wasn't aware of that detail.

As your wetsuit thickens or the most shallow depth gets deeper, I assume it would increase the discprecancy vs the method which I use. But I can see if were on a boat and didn't know what weight to use, this would be advantageous.

 

[Tom_Ivan]

Here is a very good series of articles that cover basically everything you need to know

Scuba Buoyancy Masterclass