Back Inflation Divers Can you do this?

[SeaHound]

I've noticed a difference between my back inflation BC and my old Jacket when rolling into different orientations for UW Photography.

In general, I find the Back inflation is more resistive and does take more effort (as you suggest). I also find that it is then a bit more "abrupt" when its tipping point is finally hit. I attribute the latter to being that its bladder lacks as full of a wrap-around, which would allow a smoother and more continuous transition.

In terms of full-vs-empty, the problem I'm referring to comes from the existing air bubble shifting its location within the BC, which means that it is worst when its only roughly 1/3rd full ... its behavior is just like any other piece of "Loose Gear".

IMO, if people aren't noticing these subtle differences, they need to work on their trim and control. I personally find that even a soft backpack design to me is irritating because of how it permits small changes.


-hh

Very thought provoking. I knew it had to have some kinda effect to your tilting movement. Thanks. This was a huge help. Now the resistance that you get while tilting to your side is insignificant right? Or does it become an obstacle to your photo work?

 

[SeaHound]

Took my Oceanic Excursion out on it's maiden voyage this morning, and figured I test this out, since I had never dove back inflate before. My dive buddy almost wet himself (actually he probably did), as he laughed at me swimming in all different positions. Result: no difference. I had no problem maintaining either side or on my back, for up to 40 cycles. Hope this helps!

Yes it is a big help. How much air did you have in the bladder when u were deep?

 

[bperrybap]

I dive a Zeagle Brigade. When weighted appropriately I
can get into just about any position I need to get in for
photography.
However, what I have noticed is that sometimes after I'm in
a head down position tilted to one side, remaining still, I will
begin to rotate to the other side.
What I have figured out is that wing/bladder on the brigade
is a U shape and so air can only transfer from side to side
when horizontal or slightly head up.

So if you are horizontal tilted to one side the air will
move to the higher side. If you then move to a head down position
all the air is now "trapped" on the side that was previously
the higher side. This will create imbalance if you need to rotate
to the other side without returning to a head up position.
I've figured out than when moving to a head down position
while in a sideways tilted position,
it is best to first tip heads up before going head down.
This will rebalance the air from side to side and split
it evenly between the two sides.

Maybe its just my photography style but this seems to happen
quite often to me when I'm taking pictures of things along
the bottom especially under overhangs. I'll first try coming
in horizontal and rotate to one side. But if the overhang is
close to the bottom, I'll just come in completed vertical in
a head down orientation. This allows me to get really close
to the bottom with no fear of stirring up any silt or touching
anything.


--- bill

 

[-hh]

Sorry for the delay in responding. It has been a busy year. I've been to two funerals since I wrote the below:

I've noticed a difference between my back inflation BC and my old Jacket when rolling into different orientations for UW Photography.

In general, I find the Back inflation is more resistive and does take more effort (as you suggest). I also find that it is then a bit more "abrupt"...IMO, if people aren't noticing these subtle differences, they need to work on their trim and control...

Very thought provoking. I knew it had to have some kinda effect to your tilting movement. Thanks. This was a huge help.

In simplest terms, if the air bladder doesn't have a continuous chamber all the way around you (think "inner tube"), then the air bubble within can't always keep itself on the top. This is the discontinuity that leads to Wings being 'abrupt'. Overall, since the Wing design constrains the entire air bubble to just the back, it adds stability for that orientation, but makes other orientations less stable...ie more difficult to achieve on purpose.

Now the resistance that you get while tilting to your side is insignificant right? Or does it become an obstacle to your photo work?

The Wing is an obstacle. I used to very effortlessly swim on one side alongside of pelagics such as turtles with my Jacket Style, but with my Wing, it is a noticable effort, as it tries to "right me" to face down again. Going 3/4's inverted is even worse (swimming at an angle under the subject, face up), and my photo yield is suffering because of it.

I've given myself 3 years with the Wing to see if it was just me, but it wasn't simply "old dog, new tricks": in thinking things through, I see how that it is basic physics. As such, this equipment simply does not meet my diving needs, so I'm going to be getting rid of my Wing and going back to a Jacket.

...although since my first dive back in the '70s was with a Horsecollar, maybe I'll consider one of those again, just to placate the "Jackets Are Evil" crowd


-hh

 

[dirtsport1]

My Sherwood Axis works great, even from instructing, when you on the surface half the time. As does a.... bowling ball, weight appears 'weighless' under water. When your bouyant, nothing is pushing you anywhere. Anyway, I love the style.

 

[1_T_Submariner]

I can swim sideways, I dive a Zeagle ranger. No problems other than the big blind spot.

 

[RonFrank]

I dive a BP/W so I can do anything, with no effort whatsoever!

Seriously, If one is neutrally buoyant, then it is easy to go into any position without issue regardless of what type of BC is used.

Rolling, or shifting is a sign of trapped air, and positive, or negative buoyancy. Think about it, if you are truly neutral, and properly weighted why would it result in rolling around? I have found the head stand position to be one of my new favorites for photography.......... but it takes a bit of getting used to.

 

[Cummje]

No problems for me, but I found that I had to fiddle with the weights a bit before I got the balance perfect.

 

[Firedive]

The Wing is an obstacle. I used to very effortlessly swim on one side alongside of pelagics such as turtles with my Jacket Style, but with my Wing, it is a noticable effort, as it tries to "right me" to face down again. Going 3/4's inverted is even worse (swimming at an angle under the subject, face up), and my photo yield is suffering because of it.

-hh

I think this is a perfect example of how everyone's body is different: I have never had the slightest problem, and find it easier to get into unusual positions in my transpac than in my old jacket.

 

[-hh]

I think this is a perfect example of how everyone's body is different: I have never had the slightest problem, and find it easier to get into unusual positions in my transpac than in my old jacket.

Itsw not body, because we're all within 1% of being neutral. Some systems trim out differently, which is why I gave the wing 3 years of trying different things, to see if it was just trim...afterall, weighting placement is the most common cause of diver trim & orientation challenges.


But what I finally realized was that this wasn't merely trim and that if I would have thought about it earlier, I would have realized that the problem could never be solved by trim:

My anthropometric "on side" orientation for UW photography is shoulder-up, and slightly beyond 90 degrees. The reason for this orientation is to get a "shoot up" angle to the subject to get a bluewater background while also swimming along parallel to the also swimming photo subject (turtle or whatever), which they find less threatening.

Holding my UW camera out to the side like this creates a torque, because it is around -2lbs negatively buoyant: the basic "(mass)(moment arm length) = torque" physics.

That's half the story.

The other half is that I have to have extra +2lbs of air in my BC to keep me+camera at a net of zero neutral. This +2lbs of air can have an effect too.

When I was diving with a Jacket, its air bubble would travel around me, so the extra air (+2lbs) was able to always stay on top of my centerline, so it had a zero moment arm and thus, a zero torque effect: "(mass)(zero arm length) = zero torque".

But with a wing, because there is no 'front' to its bladder, its air bubble can not ever rotate fully around the diver and thus will get "stuck" for certain orientations.

EDIT: Emphasis for RonFrank: this is the bubble effectively getting "trapped", which is utterly inherent to the Wing design: the air cannot NOT be anywhere but somewhere on your back, because there is no bladder anywhere but on your back. The jacket's bladder includes on the front, so its bubble doesn't become "trapped", but can flow to the front side of the diver.


This "on side" is one of them. It might not seem like all that much, but the average Western adult male human torso averages nearly a foot thick, so it has a moment arm, and if you work out the problem, you'll see that it is cumulative with the first one, so the total torque increases by roughly 50%.

This torque is inherent to the orientation and the sub-system components (ie, the camera), so unless this torque is continuously counteracted through effort, you'll always roll back down to where the torque moment arms are again zero.

Its a difference in diving needs, not "body". There is a new "buoyant arms" product by Ultralight for which I could upgrade my UW camera system to reduce its negative buoyancy, but each arm is $55 each (and I need 4 of them), plus four new clams at $35 each, which with S/H and tax would put me at $400 in camera gear widgets on an old Nikonos system that I'm looking at retiring in another few years...I can buy a new Jacket BCD for less than that, and it won't be obsoleted.


-hh