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68raggtop
01-24-2008, 19:38
I was talking to a DM at the LDS about some courses my wife and I want to take, and she suggested the SDI Buoyancy class. One of the reasons she gave was that it was the only one that allows it to be done in a pool environment. I am not planning on diving locally until summer (it was -15* outside this morning), so the plus is that it could be done now. I am wondering if we would get as much out of the class in the pool vs in open water? anyone have any input on that?
Thanks,
Dave

fireflock
01-24-2008, 20:17
I'd go for the pool. Buoyancy is harder in shallower water, and it's easier to pay attention to the fine details (changes in trim, weighting, etc...) in the pool.

Nothing stops you from taking what you learn in the pool and doing the same kinds of practice in the lake by yourselves.

DivingCRNA
01-24-2008, 20:46
I was talking to a DM at the LDS about some courses my wife and I want to take, and she suggested the SDI Buoyancy class. One of the reasons she gave was that it was the only one that allows it to be done in a pool environment. I am not planning on diving locally until summer (it was -15* outside this morning), so the plus is that it could be done now. I am wondering if we would get as much out of the class in the pool vs in open water? anyone have any input on that?
Thanks,
Dave

Is it with Northland divers? I took that in the pool. It was good.

68raggtop
01-25-2008, 05:32
[quote=fireflock;124407]I'd go for the pool. Buoyancy is harder in shallower water, and it's easier to pay attention to the fine details (changes in trim, weighting, etc...) in the pool.
quote]

I was thinking that also. I was curious if there was a reason the others (PADI, Naui) require it in open water?

DivingCRNA, I was at Going Under Dive Center. (I love the name of that place.)

fireflock
01-25-2008, 06:12
I imagine they would have to specify the size and depth of the pool in order to keep some pretty funny stuff from happening. Plus, if it's part of an AOW sequence or something I can see the benefit in having the class in open water.

In the MN winter, however....the pool sounds pretty darn good.

Rich

SarahBella
01-25-2008, 07:05
I would love to take that course-especially during the winter. Give me something to do in the cold, and a reason to get out and dive for practice what I have learned. Definitly!

wgt
01-25-2008, 09:15
I was talking to a DM at the LDS about some courses my wife and I want to take, and she suggested the SDI Buoyancy class. One of the reasons she gave was that it was the only one that allows it to be done in a pool environment. I am not planning on diving locally until summer (it was -15* outside this morning), so the plus is that it could be done now. I am wondering if we would get as much out of the class in the pool vs in open water? anyone have any input on that?
Thanks,
Dave

Excluding propulsion through the active movement of water, there are three factors that dictate vertical movement of the diver in the water column. The first is gravity (static). The second is mass (which may vary in the short term through the manual addition or subtraction of lead weights). The third is the volume of the diver plus his/her gear (much of this is static, but variability is added through breathing and compression of gas-filled gear [e.g., wetsuit, BCD). The latter two factors (which dictate buoyant forces) must then be blanced appropriately against gravity.

A pool (of a reasonable depth) versus the open water would not seem to be the critical issue. Rather, the important factors are 1) to understand the physical concepts of depth control (i.e., that the influence of gravity is opposed by the weight of the liquid medium [water] that is displaced by the body) and 2) to develop the physical and mental skills necessary to permit safe and productive control of depth in the water, while taking advantage of the principles of buoyancy and gravity. The pool environment is utterly adequate to satisfy both critical factors.

However, once gains have been made in either the pool or in the controlled open water environment, then they must be fortified in more challenging environments (e.g., in saline versus fresh water, at a variety of depths that alter the volume of the BDC and the wetsuit, in a current with the hands full of gear, while lugging an anchor over the bottom, or while simply changing bodily volume through regular breathing).

The purpose of adding weight to a belt or BCD is not simply to make the recreational diver sink. Rather, it is to allow the diver to use a pair of opposing forces (gravity and buoyancy) to perform a function in a safe, predictable, and ultimately enjoyable fashion. The pool is a great place to start and should not be shunned, even though the tasks can also successfully be completed in the open water. Of course, the diver should achieve their goals by whatever practical means is at his/her disposal.

The basic steps in achieving good depth control through the regulation of buoyant force are:

1. Grossly estimating the amount of weight needed accommodate the initial descent.
2. More finely adjusting weight to accommodate neutrality at critical depths under specific conditions (e.g., neither sinking nor rising with lungs half full of air while the tank is at 33 bar [about 500 psi] and the depth is 4.6 m [15 ft].
3. Gaining the skill to grossly reset volume once it has changed through variations in depth (e.g., compression/expansion of BCD and wetsuit).
4. Predicting and subtly accommodating more dynamic changes in volume associated with the tidal movement of gas into and out of the lungs.

Steps 1 and 2 can, if necessary, be invoked by an experienced buddy or instructor. Steps 3 and 4 may require guidance, but they are generally achieved naturally through the course of diving itself. Contoured sandy areas of reasonable depth (e.g., 10 m or 33 ft) are great training grounds for novices, in this regard.

in_cavediver
01-25-2008, 11:03
The pool may be a good starting point but IMHO, you can't teach it without going to OW. Simply put, managing the exposure protection required is part of good buoyancy control. That happens both at depth when its compressed and you have a larger air mass and shallower where you have less volume of air but a greater percent change of pressure per foot. Normal exposure protection is excessive in a pool and therefore you won't see its effects. Depth also plays in here as well.

I won't dispute there is much that can be learned in confined water but translating to OW is still required. These differences are the reason OW dives are required for basic certs. I think it applies here as well.

hoobascooba
01-25-2008, 11:07
my ex-wife and I when we got certified, we practiced ppb in the swimming pool by holding onto one another.

I sink like a rock, and she floats like a buoy! It was a perfect balance. (that was the only balance we found between one another) LoL.

68raggtop
01-26-2008, 11:12
Thanks for all the reply's :smiley20: It has given me a lot to ponder.



Simply put, managing the exposure protection required is part of good buoyancy control. That happens both at depth when its compressed and you have a larger air mass and shallower where you have less volume of air but a greater percent change of pressure per foot.

in_cavdiver, I understand what you are saying here. It also makes me wonder about something else, that being trim. I have been diving only warm saltwater in 3mm shorty (or less) for the last 10 years, so I will ask this as a scenario.

Diver A has on a 7mm full suit (with hood, gloves and boots) and is neutral and trim at 10' pool depth.
Diver B has on a 5mm full suit and is neutral and trim at 10' pool depth.
Diver C has on a 3mm shorty and is neutral and trim at 10' pool depth.
Diver D has no suit and is neutral and trim at 10' pool depth.
All divers are the same size and wearing the same gear except the neoprene as indicated.

As all divers descend in a lake to the same depth, will the trim of any change as they go deeper? I would guess that if the uncompressed volume (of neoprene) was higher at one end (say the head), it would change proportionately, leaving your trim the same. But I don't know if that is accurate or not. Or does the air bladder in your BCD or wing have more impact than the neoprene as far as trim is concerned?
Thanks,
Dave

in_cavediver
01-26-2008, 16:02
Diver A has on a 7mm full suit (with hood, gloves and boots) and is neutral and trim at 10' pool depth.
Diver B has on a 5mm full suit and is neutral and trim at 10' pool depth.
Diver C has on a 3mm shorty and is neutral and trim at 10' pool depth.
Diver D has no suit and is neutral and trim at 10' pool depth.
All divers are the same size and wearing the same gear except the neoprene as indicated.

As all divers descend in a lake to the same depth, will the trim of any change as they go deeper? I would guess that if the uncompressed volume (of neoprene) was higher at one end (say the head), it would change proportionately, leaving your trim the same. But I don't know if that is accurate or not. Or does the air bladder in your BCD or wing have more impact than the neoprene as far as trim is concerned?
Thanks,
Dave

OK, first, to answer you question, lets talk pressure rather than depth so we don't see minor differences in fresh/salt water. Lets say you pool is 1/3 ata at the bottom and all divers are trimmed correctly. They should be trimmed correctly at 1/3 ata pressure elsewhere to.

Now, for what changes with depth. We'll start with the center of buoyancy CB aspect. It has three component forces which determine the stable orientation and the net buoyant force. (think vector forces and free body diagrams from physics) The first component is the negative weight. This is simply your lead, tanks etc. It deviates only as the tank is used so its not depth dependent but is time dependent. The second part is the aircell. It's position doesn't change but its active force will as air is added. The last part is the exposure protection. In a perfect world, its CB also remains fixed but its force drops with increases in pressure. (it might shift slightly in the real world).

Now, if the divers CB from the aircell and the CB from the exposure protection are the same or very close, trim shouldn't change significantly as pressure increases. If these are out of line, then trim will be affected. The neat part of this is some body positioning can be used to compensate for this impact and you can maintain trim throughout the dive.

So knowing that the relativities between your exposure protection, location of your aircell, lead weights and everything else may be depth dependent, how do you figure out what to do? That is easy, you simply dive many times and notice things. Make small changes after each dive and see what happens. In the end, you shoot for the balance point of pretty good throughout the dive.

My point is that there is and can be a lot to trim and buoyancy on a theoretical level and applying that information to real diving takes real diving. You'll never get a wing well inflated in a pool without grossly overweighting a diver (which is counter to the purpose of the class right). That brings the aircell and its management out of the equation. See, a pool can only go so far.

If I could write the class, I do 3-4 dives in the 20'-40' range and on the first couple, I'd purposely create trim and weighting situations so students could really feel the problems. Then spend the last couple dives working with them to get their trim and weighting better dialed in.

68raggtop
01-26-2008, 16:50
in_cavediver, thanks for the explanation. I for one would love to take a class as you describe. I am planning on starting to do some local diving this year, so the questions will be experienced this coming season. I can hardly wait.

Super-Duper Scubasteve
01-26-2008, 17:38
I recently attended a buyoyancy class in the pool. I kind of had to do it in the pool though because I'm from NH. We did some excersices that would just be impossible to do in open water. But if we did in open water you could get some real practice on some real things. So it's a trade off I think.

Duckydiver
01-27-2008, 18:30
When I took PPB it was in an open water enviorment. Althought I have practeced buoyancy in a pool. OW Allowed the expirience of maintaining buoyancy during a multi level dive.

SkuaSeptember
01-27-2008, 19:09
This class really needs to be a combination of pool and open water. You can learn techniques and skills in the pool, but unless all your diving is going to be in warm, still, fresh water it is a huge benefit to move the class to a typical diving enviroment. The best practise I've heard of with this class is to video the pool and OW sessions and then review the recordings with the class after each session.