Optimum BCD bladder shape & location for perfect trim

[enduser]

Threads like these make me miss Tobin. @cool_hardware52 just in case.

 

[tbone1004]

Thanks for the comments so far! In response, here is some additional detail.

My trim efforts have all been wet. Shifting weight from the BC side pockets to a soft pocket weight belt had two purposes, One, to isolate some of that weight so if it was dumped I wouldn’t go to the surface like a bobber. Second, and primary, was to give me more adjustability in where the weight was located (up or down) so I could see evaluate the impact on trim, which it did. Moving the weight belt (up) towards the apparent buoyancy CG improved trim.

As I tried to say earlier, moving the buoyancy CG down would likely have the same affect as moving the weight CG uo. My U-shaped BC bladder CG would be higher than a donut’s Buoyancy CG (assuming they were the same length).

On a BP/W can the diver move the BC bladder up and down the plate to change the divers buoyancy CG? Do wing manufacturers make and market different bladder configurations to assist diver’s in obtaining improved buoyancy trim?

The donuts don't hold much air in the crossover point because there is a tank in the way, so they're mainly just there to let the air get from one side to the other. Even still, air won't just magically travel to the bottom, if you start head up, it will only follow the path of least resistance. The CG of the wings is only going to be really noticeable when you have a full bladder unless something is really out of whack. Same with moving the wing up and down a little bit. Most divers will be slightly heads up, so you aren't going to be able to move that air to the bottom unless you go head down which is a motion, not something that you'll naturally end up doing.

Dive Rite's Travel wing is the basic shape of MOST single tank bladders. Pretty square and balanced, which is fine for most use. 25lbs is enough lift for most divers, and they aren't going to have a lot of weight on them on a belt, probably diving with neutrally buoyant fins, etc.

The Voyager is 35lbs, and you can see has a much larger area in the bottom since the people that need a wing with that much lift will typically have a belt with much more weight on it, and thicker wetsuits which will require the wing to be considerably fuller during most of the dive as the suit compresses. If you are diving an AL80 with a thin suit though, you aren't really going to notice a difference because the wing is mostly empty and the top part of the wing is the same as the Travel wing

 

[BoundForElsewhere]

Man, I'd kill for any kind of buoyancy right now.

 

[Doctor Rig]

Man, I'd kill for any kind of buoyancy right now.

me too........ just getting ready!

 

[larsdennert]

Another digital diver here. What's nice about a donut over a U shaped wing is that air never gets trapped away from a vent.

People first focus on overall trim. Enough weight to go down comfortably but not so much that you can't swim a rig with an empty bladder to the surface. Thereafter people tend to focus on head to toe pitch buoyancy so they are feet down or up by moving trim weight up and down the BC, changing fins or ankle weights. Third focus should be on axial trim. If you go to roll onto your back, is that aluminum tank making you struggle and flip you back? Is that steel tank and plate making you go turtle? Changing your roll center of gravity with trim weight can help you stay rotated 90 degrees or swim in any position.

I prefer a light weight plate that I can travel with and attach extra lead weight to if needed for drysuit diving.

 

[MichaelMc]

Would a BP/W set up inherently give the diver the best versatility in optimally aligning their buoyancy and weight CG? If yes, Is there something specific I should look for in a BP/W?

To me, yes, a BP/W gives you more options to adjust trim. It also puts some more weight were you need it from the start, the plate if it is steel. You can attach weights to the very top part of the plate if that is what you need. You can add it to the bottom, or any where in between. All the straps are 2", so you can easily add weigh pockets to them. Some places that is out of the way, like on the hip belt. Some put them very high up, on the shoulder strap tops, but can be a bit in the way or a minor pain putting it on. But you have the option.

How much weight are you dealing with? If it is say 5-6 lb, then a steel plate uses all that up and puts it in a handy spot, but does not give you options to move it. If you have 6-10 pounds left over after the plate, that should be enough to put wherever you need it to get in trim.

Before someone jumps on me, yes you can trim out in a jacket or integrated BC. But the options on how to do that may be trickier. You generally only have a few spots close to the body, the hip and one trim spot. You can add to the cam bands, but as mentioned that affects front/back trim.

BP/W has a whole infinitely adjustable spot along the back where you can try weights, with zip ties and gorilla tape, till you find just the spot for you. Making the gear your customized ride and then diving it. Because you can.

With the Zeagle, you might split your weights so you have some you can hold in your hand. Two one pounders, a two pounder, or two two pounders. A small amount. The point is to see if there is a spot higher on the body where a small amount of lead will put you in trim.

Then take those out, hold them in your hand(s), and see how far up your body you need to move them to get to where you are in trim. If you've got some bungee loops on them, during that dive you could bungee them just temporarily to your front straps at that point to see how that weight distribution works. Now, if you had a spot to store them at that point up your body, you would be set. A BP/W gives you such a spot all up and down the back. Also up and down the shoulder straps but that clutters them up unless you use small flat one pounders, and the back is cleaner.

It may be that you can get in trim with two two pounders up higher than where your trim pockets let you put them.