Whats my problem with sinking (weights) ??

[DevonDiver]

What NWGratefulDiver taught me, when I was new, was to hold my BC inflator hose up and vent it, and INHALE. Just as my mask hit the water, I was to EXHALE and hold it. At the same time, I was to cross my ankles with my knees slightly bent. This kept me from kicking myself back up, and also, because of the bent knees, tended to rotate me into a more horizontal position for descent, which meant that if I did kick, I wouldn't go back up.

Hope some of these tips help you. Difficulties descending are very common with new divers, and although proper weighting is necessary, the solution is rarely more weight.

TSandM pretty much covers it.

Common problems on descent:

1) Failure to exhale and empty lungs.
2) Failure to calm breathing to a slow and steady rate.
3) Failure to fully deflate BCD.
4) Instinctive fin movement, causing upwards force.

The instinctive reaction to these problems, and associated inability to descend, is to add more weight. This is dangerous for several reasons. It will also make you much more uncomfortable throughout the dive and cause you to burn your air quicker.

Ideal Weighting

The best way to confirm your weighting requirements is to analyize your safety stop at the end of the dive, when your tank is at minimum diving pressure (50bar/500psi). You should be able to easily hold your safety stop without floating upwards. Examine how much air you have in your BCD. Is it mostly full or nearly empty?

If there is a lot of air in the BCD, then start removing weight a small amount at a time. As you do this, you will have to remove air from the BCD to compensate. Slowly, through trial and error, remove weight and air, until you reach a point where your BCD is virtually empty.

If you can reach a point where you have hardly any air in your BCD, your tank is at minimum pressure (50bar/500psi) and you cannot possibly remain floating at your safety stop with less weight - then you have achieved good weighting.

The end result should be that you don't ever need to add much air to your BCD to attain neutral buoyancy. This has a knock-on effect of improving your overall buoyancy control, especially on ascent, and should improve your horizontal trim and lessen water resistance as you swim (you use less air).

Aim to repeat this assessment every 20 or so dives, as your weighting requirement will decrease with experience.

 

[SilverNU]

All great replies..

My info:
Im usually wearing a 5mm full wet suit,
a skin suit 1mm under my wet suit,
3mm gloves,
boots
Al80 tank

I have 6 lbs of weight on the back of my BC (tank weights)
I also have 8 lbs of weight in my BC (4 on each side)

The situation went like this..

I start the dive... find that its hard to get down with my BC deflated.
Figure I need more weight..
Went to the boat to add some weight.. at this point I tried to do a weight check.. with everything listed above.. (the tank is nearly full)
Deflated my BC, took a breath, then stated to sink a few feet.

Maybe I didn't have all the air out of my wet suit... maybe I need a couple extra pounds.
Maybe I should do my weight check with an almost empty tank.

The only think that seems weird to me is that its hard to sink that initial 10 or so feet.. then I seem to go down as needed... eventually need to inflate my BC some to stay off the bottom.

 

[TSandM]

Oh, but you see, what you are experienced is how it should be.

You are using neoprene exposure protection. Neoprene insulates by virtue of tiny gas bubbles caught in the material. As you descend, those gas bubbles deflate just as everything else containing gas shrinks as the pressure increases. As they get smaller, they displace less water, so they are less buoyant. A thick wetsuit can lose a LOT of its buoyancy in deep water. This is normal, and is part of the reason you need a buoyancy "compensator". The air in your BC compensates for two things . . . the gas you intend to exhaust into the water (which has weight, difficult as that is to imagine) and the buoyancy your exposure protection loses as you descend.

Anyone diving fairly thick neoprene (and if I read you correctly, you are using about 6 millimeters of neoprene) will experience decreasing lift as they go down (thus more gas in the BC) and rebounding lift as they ascend (thus a need for more rapid venting of the BC). This is normal, and you will get used to it.

 

[SilverNU]

so you are saying its normal to have a little trouble getting down those initial 5-10 feet (as I experience) and once I get compressed enough I tend to find it much easier to sink?

 

[DevonDiver]

Yes... there is a 'critical depth' that you reach, where compression of your exposure suit will decrease your bouyancy enough to make you easily negative. From that point onwards in your descent, the equation changes and you need to start adding air to the BCD.

The first few meters is where you are most bouyant. A few small issues such as deep breathing and involuntary finning will stop your descent. Iron out those problems and it will all seem very easy

 

[wantedule]

Well, I agree with Submariner ! A little more weight do no harm ! You have plenty "room" to balance with your jacket instead having a big problem at the end of the dive with empty tank- grabbing the rocks from the bottom ! LOL !

 

[Quero]

so you are saying its normal to have a little trouble getting down those initial 5-10 feet (as I experience) and once I get compressed enough I tend to find it much easier to sink?

Yes! The descent for those first few feet is very gradual. As you descend the air in the fabric of your neoprene wetsuit becomes compressed and no longer offers the same amount of buoyancy, so you begin to descend a little faster. The deeper you go, the more pronounced the effect. If you go deep enough, you will need to add air to your BCD in order to compensate for the lack of sufficient buoyancy provided by your wetsuit and your lungs to keep you neutral (and prevent you from ending up on the bottom).

 

[SilverNU]

all of this make more sense now..

I appreciate everyone's replies.

Sometimes I do find when I do get to the bottom I become a rock grabber
and
on the top I guess I would be an air grasper

 

[Quero]

Well, I agree with Submariner ! A little more weight do no harm ! You have plenty "room" to balance with your jacket instead having a big problem at the end of the dive with empty tank- grabbing the rocks from the bottom ! LOL !

The circumstances here where I do most of my diving prevent me from conducting weight checks with nearly empty tanks on ocean dives. But I do know roughly how much the air in a full tank weighs as opposed to a nearly empty one, so when I get my students/new divers to weight themselves at the beginning of a dive, with a full tank, we get them floating properly and then I hand them enough additional weight to compensate for the fact that the tank will be lighter and tend to drag them up at the end of the dive.

However, I wouldn't make a blanket statement like A little more weight does no harm since I think it can instigate all sorts of problems. Divers should be properly weighted rather than over-weighted or under-weighted, and the weight should be distributed appropriately. But that's a different topic.

 

[SNorman]

If an object is negative it won't sink five feet then stop, it will keep descending. So, I think you're either breathing in too much or finning. You may not have enough weight, and descending past a certain distance compresses your wet suit and BCD enough that you're sufficiently negative.

I had a similar problem when I lost 10lbs of weight from a weight integrated BCD and didn't realize it. It was really hard to get down (but somehow I managed to) but then was unable to hold the safety stop at the end of the dive.

I would try making sure you have all the air vented from your BCD, you're exhaling sufficiently, and not finning first.