The disadvantage of a BP/W

[Storker]

I've been using a BP/W for about a year and a half now, transitioning via a back inflate BCD from my initial jacket BCD. Generally, I'm very happy with the BP/W system, and being an UW photog, the clean front that I have wearing my harness instead of an inflatable jacket with front pockets is a clear advantage over the jacket BCD.

However, there's one situation where a BP/W and a back inflate shows a clear disadvantage compared to a jacket BCD: When you want to roll onto your back. When viz is good, I love to roll over on my back, looking up at the surface and the light playing there. I love to lie on my back, looking up, enjoying the view. But when all of my buoyancy is located above my back, it'll lose volume by about 0.5m/2" water column when I roll over, and Boyle takes over. So I'm less buoyant, and I start sinking and have to compensate by adding air to the wing. When I was in a jacket BCD, the buoyancy air just moved around my torso and was pretty much at the same pressure, and I didn't have to watch my depth.

I'd love to be able to just roll over and enjoy the view upwards, but it seems as if physics are heck-bent on taking that small joy away. It's a small price to pay for the advantages of a clean front, but still...

And don't get me started on going away from horizontal trim and suddenly losing buoyancy because my DS shoulder valve starts dumping.

 

[Insta-Gator]

I would suggest you have not tuned your weighting. I am able to roll over on my back, invert to a head down position, assume any position I like and do not experience the problems you describe. If you can, try to reduce the amount of weight you carry. There should be a bare minimum amount of gas in your wing while diving. If you are using the wing to excessively, you probably find yourself adding or releasing gas as you make minor changes of depth. That should not be the case if properly weighted.

YMMV

 

[tomfcrist]

Yeah, I've got to say I've never had that issue. I had some issues with buoyancy and trim when I started diving doubles again after a 10 year layoff, but once dialed in I can't remember a time when I couldn't roll over or even invert without issue.
A couple inches of depth change shouldn't be causing that much of an issue. If you were to remain belly down while horizontal and neutral, what would happen if you closed your eyes? The change in your WOB from rolling may be screwing with your buoyancy.

 

[Storker]

A couple inches of depth change [...]

It's more like half a meter (almost 2').

And naturally it's more of an issue at the beginning of the dive when I have about 3L of air in my wing than at the end when it's almost empty.

 

[decompression]

It can be common that when we flip, our legs bend at the waist and "pull" us down due to the large shift in weight. We rarely think about the change of leg position. Be very conscious of this when flipping. The reason a jacket is less subject to this is the lower placement to the hips and around the belly of the cells.

Just thought and practice to overcome....


Sent from my iPhone using Tapatalk

 

[Storker]

It can be common that when we flip, our legs bend at the waist and "pull" us down due to the large shift in weight. We rarely think about the change of leg position. Be very conscious of this when flipping. The reason a jacket is less subject to this is the lower placement to the hips and around the belly of the cells

Good point, thanks.

I assumed it would be less of an issue since I usually dive dry, with a significant amount of my buoyancy in my suit (I'm using single tanks, strictly rec, so the buoyancy swing from the start to the end of my dive is moderate), but the difference between diving a DS and diving a WS has so far been minor.

 

[Superlyte27]

Lol, suck it up buttercup and hit the inflator button.

 

[redacted]

I do not think I have ever experienced such a problem. But that may just be a disadvantage of warm warter diving.

 

[tbone1004]

I swap upside down for a while in a few different caves this week because the ceiling is gorgeous. Non issue, just take a bit bigger breath and stabilize. If you're at depth it is even less of an issue. That said, your point is valid that rolling over in a jacket is easier, but considering on my dive in P3 I went a total of about 3500ft, and maybe 200ft of it was upside-down, I'm really not going to argue that much

 

[halocline]

It's more like half a meter (almost 2').

And naturally it's more of an issue at the beginning of the dive when I have about 3L of air in my wing than at the end when it's almost empty.

Why don't you ascend a foot or two then your bubble will be at the same depth?