Something's wrong with my bouyancy?

[BRT]

Because once i'm at the bottom, my chest sinks and my feet float higher - made it hard to swim comfortably.
I'd like to be in a state where my upper body could go a fit higher than my feets

You have a double layer of neoprene on your upper body. So you are losing much more buoyancy on the upper part of your body than on the lower part as the neoprene compresses with depth. Not much to be done about it unless you change to a dry suit.

 

[alex_can_dive]

are you sure the tank you are using is a high pressure 100 ? cuz if you are, something doesn't seem right here. those are very heavy tanks. and they do not become positive at any time.

you said you are wearing a 8/7mm suit ? is it a one peice, or are you wearing two layers ? what exactly are you wearing ?

at home i dive a low pressure 77. so it would be lighter in the water than the HP100. if i wore a full 7mm wet suit with hood and gloves, i would be adding about 14 lbs of lead. and i am about 180 lbs.i add about 18lbs with my dry suit and cold water undies.

Yes. I’m positively sure.
I wear the 8/7 aqualung Solafx with no layering. 5mm boots and 2 mn gloves.
The tank is steel HP 100cf

 

[alex_can_dive]

You have a double layer of neoprene on your upper body. So you are losing much more buoyancy on the upper part of your body than on the lower part as the neoprene compresses with depth. Not much to be done about it unless you change to a dry suit.

Here’s another problem. Not only does my upper body sinks, when I hold a full breath, it won’t lift up from the bottom. I think that should indicate that I’m a bit overweighted.
And yet - reducing the weight to 12lbs makes it impossible to descend.

 

[diver0008]

Here’s another problem. Not only does my upper body sinks, when I hold a full breath, it won’t lift up from the bottom. I think that should indicate that I’m a bit overweighted.
And yet - reducing the weight to 12lbs makes it impossible to descend.

You can add some air to the bcd anytime to increase your buoyancy at depths, sort of what it's for from my understanding.
You will figure out the weighting with experience; don't worry - you're probably not too far off.
But trim seems to be your primary problem. Consider shifting your weights back, maybe with a belt instead of using the bcd pouches, as others have suggested.

 

[Wibble]

You need the weight you need. Some people see weight as some form of anti-competition -- "I don't use any weights", etc.

Being overweighted is simply bad for you -- you'll use more gas and spend a lot of time adjusting your buoyancy when you change depth, not to mention shooting to the surface as all that gas expands if you don't dump it. Remember for every kilo (2.2lbs) that you're overweighted, you need to displace 1 litre (pint and three quarters -- that's a proper 20 fluid ounce pint). At 30m/100' that's four litres of gas in your BCD.

Whilst ankle weights are a bit naff, they can solve trim problems if you're diving with lightweight fins (and you cannot adjust your centre of buoyancy by moving weights around).

 

[Jayfarmlaw]

Hmmmmmmmmm.... can you move your tank down on your BCD?

Does your trim change if your arms are crossed close to your body or straight out front like superman?

Could you get by with 3mm boots or maybe a heavier rock boot type that will fit your fin? 3 mil boot and a wool sock?

Have you dove any different BCD's? May I tell you about the glorious and Devine freedom a backplate and wing can give you here at the Chairman's Church of Scubaboard? That's a joke, but some BCD's just don't work for some people. Some BCD's trap air? When your butt high, have you tried to dump air from a hip dump? Back inflate BCD?

Pool time is your friend here. Change it up until you find the solution.

If your able to maintain your safety stop with minimal air in your bcd, you don't have too much weight.

7mm is a lot of neoprene, is it new? New neoprene takes a while to compress. I had to swim mine down for lots of dives before it was consistent.

Lots of possible solutions, you just have to find the right one.

Good luck.
Jay

 

[John C. Ratliff]

Two of them are both dive instructors with 1000+ dives.
Hmm, I only have my weightpockets in the BCD. I could put some on the tank but that would not fix my legs-floating issue, right?

I wouldrecommend that you take some weight out of the BC, put itm on a weight belt, and trz that. This will get the distribution better on the horizontal axis. If that does not work, then try all weight on the weight belt. Try this before ankle weights (I do not like ankel weights). Weight belts made of rubber work best.

seaRat

 

[lowwall]

Here’s another problem. Not only does my upper body sinks, when I hold a full breath, it won’t lift up from the bottom. I think that should indicate that I’m a bit overweighted.
And yet - reducing the weight to 12lbs makes it impossible to descend.

Neoprene's ability to insulate primarily comes from little air bubbles trapped in the material. As you descend those air bubbles get compressed and the suit becomes less bouyant. This becomes a very noticeable issue with thick suits like you are wearing. For example, it appears your suit is somewhere between 20-24 pounds buoyant at the surface. At 100', it is only going to be 5-10 pounds buoyant.

Most of the material in the suit, and thus the loss of lift, is going to be in your upper body. So of course your trim is going to change as you descend. It's just the nature of the beast. If you can't figure out a placement of your weights and wing that work well at all depths, I'd optimize for trim at depth. It's better to be top-light at the surface than top-heavy at depth.

The other option is to switch to a trilam drysuit.

 

[scubadada]

Sorry if this has been covered. Just do a proper weight check. Ascend to your SS. nearly empty cylinder, no air in your BC. You should be able to easily hold the stop and make a slow, controlled ascent to the surface. A trim problem is different, and requires redistribution of your weight.

 

[Scuba Client]

Please advice me on how much weights is right for me?

I'm 120 lbs and wear an 8/7 wetsuit, diving in the ocean (New England, if it matters).
I usually wear 14 lbs. Everyone keeps telling me that's too much weight. Sometime I feel it at the bottom where my upper body sinks a bit lower than the legs.

But when I do the usual test at the surface (you know, hold a breath and see where I float), with 14lbs, I float at nose level. There were times where I jumped off the boat with completely deflated BCD + 14lbs, I still float back up without even kicking.

I've tried to go with 12lbs once and I literally could not descend. My two buddies had to pull me down. Once I'm down, I'd go around at the bottom for a few minutes and as soon as I took a normal full inhale, I started to float up. The whole time I could not take an inhale that lasted more than 2 seconds.

How do I fix this?

Wetsuit compression is your main concern.