Trim/buoyancy conundrum

Alright, this is a bit of a theoretical question, so bear with me...

I'm nicely in trim in shallow water, let's say 10-15 ft, and I'm not overweighted. Wearing my usual 5 mm full suit and booties.

Now as I go deeper, my suit compresses and loses buoyancy. It does so evenly across the entire fabric, head (well, shoulders) to toes. I put air in my BCD to compensate to become neutral again.

So now I've lost buoyancy across my entire body, including my legs and feet, but have added buoyancy only around my chest/torso. This makes me leg-heavy and puts me out of trim.

What would be the proper way to correct this? Can it be fixed at all? The only way I can think of is to adjust my posture trying to compensate for this shift in buoyancy, but that seems awkward. Any other ideas, what am I missing? And, judging from the lack of other posts discussing this, why do I seem to be only one having this problem? Logically it seems this should be happening to everybody?

dfx:

Alright, this is a bit of a theoretical question, so bear with me...

I'm nicely in trim in shallow water, let's say 10-15 ft, and I'm not overweighted. Wearing my usual 5 mm full suit and booties.

Now as I go deeper, my suit compresses and loses buoyancy. It does so evenly across the entire fabric, head (well, shoulders) to toes. I put air in my BCD to compensate to become neutral again.

So now I've lost buoyancy across my entire body, including my legs and feet, but have added buoyancy only around my chest/torso. This makes me leg-heavy and puts me out of trim.

What would be the proper way to correct this? Can it be fixed at all? The only way I can think of is to adjust my posture trying to compensate for this shift in buoyancy, but that seems awkward. Any other ideas, what am I missing? And, judging from the lack of other posts discussing this, why do I seem to be only one having this problem? Logically it seems this should be happening to everybody?

Click to expand...

If you are using a weight belt, then this is weight on the foot side of the fulcrum....so moving the weight to the dead center ( backplate) will mean less weight without compensation, at depth....

If you have larger legs than most, that will mean more rubber in the wetsuit, and more air in the cells to change buoyancy.

Of course, if you had big long freedive fins, they are like big wings on a plane, so with any forward motion at all, they will keep you horizontal during the glide.....you get a huge glide with freedive fins you wont get from jets or other scuba fins

No, you are correct, you may need to adjust your posture to counter changes in buoyancy properties. If you are in trim position, you can extend your legs somewhat, keeping your fins flat. The water pressure will help keep you in place and is more than enough to compensate for a compressed suit.

Arm/Leg position and breathing adjustments are usually enough for me to stay in trim. Sometimes I might tighten/loosen my saddle straps to reposition my tank, but that's about it.

dfx:

Alright, this is a bit of a theoretical question, so bear with me...

I'm nicely in trim in shallow water, let's say 10-15 ft, and I'm not overweighted. Wearing my usual 5 mm full suit and booties.

Now as I go deeper, my suit compresses and loses buoyancy. It does so evenly across the entire fabric, head (well, shoulders) to toes. I put air in my BCD to compensate to become neutral again.

So now I've lost buoyancy across my entire body, including my legs and feet, but have added buoyancy only around my chest/torso. This makes me leg-heavy and puts me out of trim.

What would be the proper way to correct this? Can it be fixed at all? The only way I can think of is to adjust my posture trying to compensate for this shift in buoyancy, but that seems awkward. Any other ideas, what am I missing? And, judging from the lack of other posts discussing this, why do I seem to be only one having this problem? Logically it seems this should be happening to everybody?

Click to expand...

Couple of thoughts.

- When was the last time you did a thorough buoyancy check? Any weight you carry with you that you don't need is going to exacerbate this problem at depth.

- Your trim may be a little foot heavy to start with. Try moving 2kg of weight up to the cam band (especially if you have pockets for it) and compensating for being a bit head down in shallow water by tilting your head up, bending your knees (or extending your legs depending on what you can make work) and pushing your belly out (hole the back a bit). Don't overdo it or it won't be comfortable, but the point is that it might be easier for your to compensate for being a bit head-down in shallow water than to compensate for being head-up in deeper water.

- I'd try those things first. I hope you get more suggestions. I dive in a drysuit 99% of the time so I'm probably not the best person to be giving advice on this point.

R..

I move some weight from my belt to the cam bands, still a bit foot heavy with the jets. Don't get carried away or when you go vertical head down you will just roll over on your back, embarrassing to say the least.



Bob
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I may be old, but I'm not dead yet.

I have this same problem. I tend to be a bit foot heavy at the beginning, and head heavy at the end. I try to manage the bubble in my wing, keeping it toward the butt when I'm leg heavy and toward the shoulders when I'm head heavy. This is much easier to manage in a drysuit, but it's not always drysuit weather.

I would suggest that the first step would be to reassess your weighting - not just positioning of it, but the total weighting you use. Overweighting can lead to the issue you are experiencing. As you go deeper, the suit loses buoyancy. As you go deeper, the suit loses buoyancy and you add air to the BCD to achieve neutral buoyancy. However, if you are over-weighted, then you must add much more air which pulls the upper part of your body upward. Therefore, start by reassessing your weighting needs (i.e. you should float at eye level with no air in your BCD while holding a normal breath and slowly sink when you exhale - adjust your weighting accordingly.). I also suggest adjusting your weighting at the end of the dive (after the safety stop) with the assistance of your dive buddy. The weighting goal is to be able to maintain neutral buoyancy with little or no air in your BCD with 500 psi in your tank at the end of the dive. If you are still diving with the weighting you used in open water then overweighting is likely the culprit. Most divers find with additional experience that they become more relaxed and are able to use less weight. I'd only start moving weighting to other locations (such as the cam bands) after ruling out overweighting in general.

I use 41 pounds with an AL80 and 7 mil farmer john wetsuit and am not overweighted. My legs/feet are like stones and fins negatively buoyant. I get horizontal by putting 4 pounds each in my BC shoulder pockets and hoisting the weight belt way high. Using suspenders makes this easy to do and maintain. Same procedure when I use my shorty with 18 pounds. Once in a while I use just the 7 mil top, and am really out of whack-- so I attach small boat bumper floats to my ankles (not when others are around.....). I guess you do what you have to do.

You dive the gear, the gear doesn't dive you.

Make sure your weighting is right (able to swim up w/empty BC+full tank, able to stay at 15' with empty tank and ~empty BC). Get the weight over your lungs (the most floaty part of your body, generally) by using a backplate or weights on your cam bands. Put the rest on a belt. Go scuba. A lot. See how your attitude in the water changed based on body position and posture. Legs in = center of gravity has moved forward. Legs out = center moved back. Arms out = center forward, arms back = center back. Your noggin contributes a lot to your trim, too. Some people have an empty space between their ears and it makes them float more.

Caveats: If you put all your weight on your waist, you're gunna have a bad time.