Air shifting?

[gr8jab]

Hi all,

I'm diving a Seaquest Malibu (back inflate BC). I'm a vacation diver with a couple of week long trips each year. I do a weight check, but spend the first few days shedding lead and getting adjusted. By the 3rd day, I'm using minimal air to remain neutral at depth and can maintain my safety stop on the way up. Feels good.

I have noticed that I'm sometimes tilted in the water. At the beginning of the week, it is more pronounced, but gets better as I use less lift air later in the week. Sometimes I can balance the air or shift the tilt to the other direction by maneuvering my body around. There is a path between sides of the bladder, both at the top and bottom. The one on the bottom is rather narrower than the top.

My questions are:

Should the air move more easily from side to side, and even naturally balance itself? Maybe if the path between left/right is narrow or pinched off by tacoing, it can't move easily.

The BPW doughnuts I've seen seem to be more symmetrical. Do they naturally balance better than my Malibu BC?

Does 'right sizing' a BPW wing minimize this problem?

Does moving more wight to the back, closer to the wing, minimize the tilt forces?

Is this why I see some wings with elastic or bungee?

Thanks!

 

[tbone1004]

completely normal to shift. If it's noticeable, it is likely that you are overweighted and the bubble is quite large, you've addressed that with shedding lead towards the end.
It should move easily, if it doesn't you can't dump all of the gas which is dangerous.
The balance is going to be dependent on the aspect ratio of the wing, length to width.
It is not the reason you see elastic or bungee on wings.

 

[gr8jab]

completely normal to shift. If it's noticeable, it is likely that you are overweighted and the bubble is quite large, you've addressed that with shedding lead towards the end.
It should move easily, if it doesn't you can't dump all of the gas which is dangerous.
The balance is going to be dependent on the aspect ratio of the wing, length to width.
It is not the reason you see elastic or bungee on wings.

Higher aspect ratio (long and skinny) is better? Shorter moment arm?

This also implies that right-sizing the wing capacity is important to keep the air close to the C-of-G?

 

[tbone1004]

Higher aspect ratio (long and skinny) is better? Shorter moment arm?

This also implies that right-sizing the wing capacity is important to keep the air close to the C-of-G?

correct. Long skinny wings shift left in roll, but obviously more in pitch. You are less likely to notice the pitch side though as few people rapidly go from head up to head down or vice versa. Downside with long wings is getting them to work on things like AL63's

 

[NAM001]

the larger the wing the more room for air to move. i CAN WEAR A 30 and be fine then switch to a 40 and it is a mess. getting the right size is important. The tank you use is also a factor. 7 inch vs 8 inch especially in the crossover areas and mostly the bottom. some people prefer horseshoe rather than doughnut wings. long and skinny as others have said allows long movements top to bottom. In my experience you want the wing to wrap around the underside of the tank so to help self prevent the air from moving. it works better with large diameter tanks than skinny ones. so long as you use a skinny tank the wing will have a tendency to pull straight up. The wider the tank the wing has to be pulled horisontally more to the under sides before pulling up and that pinches off or reduces the size of the wing air space. To then fill it you have to force air under the tank edge (no biggy) which is handy for initial water entry with full tank weight. a 30# wing will have IE 20# lift on the side of the tank and 10# under the tank. It all makes a difference who the manufacturer is. you can look at the wing from the center of it and see how wide it is where the tank lies. if the wing is internally 6 inches than an 8 inch tank has 2 inches of it under the tank and the lift will press against the tank as it wraps and block the free air space that allows the air to move top to bottom. A 7 inch tank will do it less.

 

[AdivingBel]

Smaller wings are nice for warm water dive travel (you said you're a dive traveler so I assume warm water ??). Easy to pack and sleek in the water, but maybe not as versatile if you're also cold water diving. Do you keep a log? There's no real reason to start each trip diving overweight if you're diving in known, similar conditions and gear. At least with warm water diving, if you're weighted correctly you shouldn't have much air in your wing/bcd while diving so the form of the wing really shouldn't matter. Good luck.