Have to kick to decend from surface but very negative on the bottom

[Vitaminless]

Hi,
During my last dive, I found myself have to kick in order to decend in the first couple of feets and once I passed some certain depth, I started to decend pretty quickly.
On the surface, I tried to empty my lungs and still could not decend without kicking.
On the buttom, I had to pump a lot air into my BC to keep neutral.
Am I underweighted or overweighted?

 

[Edward3c]

Hi,
During my last dive, I found myself have to kick in order to decend in the first couple of feets and once I passed some certain depth, I started to decend pretty quickly.
On the surface, I tried to empty my lungs and still could not decend without kicking.
On the buttom, I had to pump a lot air into my BC to keep neutral.
Am I underweighted or overweighted?

Before you can get any useful feedback we need to know what kit you were wearing, especially the suit.

 

[Vitaminless]

Before you can get any useful feedback we need to know what kit you were wearing, especially the suit.

I was diving a XXL 5mm in fresh water. That is a lot of buoyancy on the surface I guess?

 

[happy-diver]

Sounds perfect to me, learn your configuration over a couple more dives and see what happens

 

[Imla]

Proper decent!


Usually people are taught "Exhale, empty bcd, decend" without being told that order is important!


1. INHALE - Hold your breath (Yes, you are on the surface, completely safe)


2. Empty drysuit while holding your breath (If applicable)


3. Empty BCD while holding your breath (You will still be floating... )


4. Cross your legs (You might be inadvertantly be swimming to keep balance...)


5. Exhale while leaning a little bit forward


The result of this will be that you are 3m+ below and horizontal before you feel the urge to breathe, and hence, you will be able to stay under when you inhale instead of popping to the surface again.


This gave me the calm that I needed to start my dive properly. No stress. No fuzz. Properly weighted!


ORDER is relevant!

 

[lowwall]

I was diving a XXL 5mm in fresh water. That is a lot of buoyancy on the surface I guess?

Exactly. Neoprene gets most of its insulation capability from little bubbles of gas (usually air) trapped inside the fabric. Those bubbles also give the fabric positive bouyancy.

As you descend, the bubbles, and the bouyancy they provide, shrink under the increased pressure. At 100', the bubbles will be 1/4 the size they are at the surface. This can result in as much as 10 pounds of difference in bouyancy compared to the surface for an XXL 5mm.

 

[steinbil]

Am I underweighted or overweighted?

To test it, go to the shallows 10-15ft with a dive buddy, somewhere with a safe bottom composition (sand is ideal), and empty your BCD completely - make sure you squeeze all the air out. You should now be slightly negative and sink to the bottom. Purge or breathe down your tank to 500psi/30bar. On a full exhale you should sink to the bottom. If you don't you're underweighted. Make a full inhale, and you should float off the bottom. If you don't you're overweighted. To fix your weighting in this scenario, pass 1-2lb weights to/from your buddy until you reach the perfect weighting.

PS.
Emptying the air from your tank can seem scary, but you should do this in the shallows where you can easily go to the surface if needed, and you should have a buddy ready to donate if needed. Also make sure that you have weights you can dump, both to adjust the weighting, but also to get to the surface if you happen to be very overweighted and something happens to your BCD. The optimal place to do it is a beach with no surf where it's easy to climb out.

PPS.
Remember that neoprene will compress and lose buoyancy as you descend. The thicker the neoprene, the bigger the buoyancy change. Which is why some people don't dive deep with thick wetsuits, but use drysuits instead. Otherwise you might risk being overweigthed at the deepest part of your dive, which is both uncomfortable, and a possibly safety issue.

 

[Edward3c]

I was diving a XXL 5mm in fresh water. That is a lot of buoyancy on the surface I guess?

But what about your BCD (some have neoprene in the back plate for comfort), what cylinder do you use.

With wetsuits its normal for small air bubbles to still be attached to the outside of the suit; over a large area it makes a difference. They drop off during the dive. Additionally, are you venting all the air from inside your suit, because any trapped air will have an impact.

Do a proper buoyancy check at the end of a dive.

 

[Scubagermany]

When I got my new W7 7mm neopren I had trouble going under at all.

It was just possible with a lot of extra weight, going facedown and kicking. Every few meters I had to stop, get upright so I could equalize and than go head down again kicking.
At about 10m it was all better and I could descent normally so it was all due to the buoyancy of the 7mm.

 

[clownfishsydney]

Normal. So long as at 5 metres (18 feet) you are not buoyant.