ascending and descending

[jgaff]

I had my second dive yestersday after my owd cert.Both dives i had trouble getting down so i added more weight 34pds total. Now after the extra weight was added i had no trouble dive was excellent. My first dive i ascended perfectly but yesterday my gauge read 70 bar so i started to come up but couldnt if i came up 5m and let a small bit of air out of my bcd i would drop back down. I started to panic a bit as ithought my air was running out and i never dumped air out of my bcd and i shot out of the water by about 2 feet.The dive master wouldnt let me take my second dive as a result of my rapid ascent.What am i doing wrong and will these skills get easier with practice. I also used my new bcd and wetsuit for the first time yesterday.
Totally hooked on this great sport.

 

[LI Diver]

Not enough info. What thickness wet suit? Sounds like a lot of weight. What type of build do you have? Do a eye level surface weight ck refer back to your manual/video or instructor before you think about descending again!

 

[Ber Rabbit]

You need to do a proper weight check with your new gear. While 34 lbs sounds like a lot it could be close to but still over the amount of weight you need if everything in this list applies to you:
1-you are wearing a 7mm suit
2-you are diving in salt water
3-you are a little anxious and not breathing properly
4-you are a fairly big guy (260+ pounds) or have a high percentage of body fat

When you first get in the water there will be air pockets in your wetsuit that increase it's buoyancy until the water runs down your back and fills them up. Some divers who are weighted for neutral buoyancy at 15 feet with an empty bc and 500psi in the tank have a bit of trouble descending the first few feet (usually 6-8). The feet first surface dive you were shown in your OW class will give you enough momentum to get down to 6 or 8 feet.

There are some really good threads here on the board about doing proper weight checks. You are a new diver and should not be carrying more lead than you can safely swim to the surface.
Ber :lilbunny:

 

[Matsya]

Prima facie it sounds like you are over-weighted especially when you say that on your ascent when you let air out of your BCD, you tend to drop down.

Proper weighting is a key to achieving neutral buoyancy and is something to be really worked on.
You will find numerous helpful threads in ScubaBoard on proper weighting techniques.

Are you completely emptying your BCD when you descend? Your weighting should ensure that you have as little air in your BCD as possible when you descend. The more the air in your BCD, the more weights you will need to descend.

You should be adding small amounts of air in your BCD during the dive only to compensate for changes in buoyancy - for example due to wetsuit compression.

Yes for me it got better with practice. With a 3mm wetsuit I now use 8 pounds of weight in sea water and dive with a practically empty BCD. I weigh 150 pounds.

 

[TSandM]

The key is dosage.

Think about a thermostat -- The goal is to keep the room at the same temperature. When the temperature goes down a little bit, the thermostat turns the heat on. What you don't want is a thermostat that waits until the temperature has gone down 20 degrees, and then heats the room until it's 20 degrees too hot before it turns the heat off.

It's the same with buoyancy. What you want is to stay as close to neutral buoyancy all the time as you can. Then you can control your depth with your breathing and with your attitude in the water. The problem is that, as you go up and down, the amount of air you need in your BC to be neutral changes, and you need to adjust it. In the beginning, you don't have a sense for exactly when you need to make these adjustments, and how large they need to be. You wait too long to make changes, and then you tend to undershoot or overshoot -- you're a bad thermostat. As you gain experience, you realize how small the adjustments need to be, and you get much better at evaluating the sensations that tell you whether you have done enough (or too much).

Overweighting, common with students, makes the job harder, because the extra weight requires that you put more air in your BC to get neutral in the first place, and therefore the buoyancy changes with the proportional expansion of the air as you ascend are bigger, and harder to control.

It sounds as though you might benefit from a little more time in a pool, working on these ideas. Can you talk to your instructor about that?

 

[Louma]

It does get better with practice. You should be able to start sheading pounds shortly. But first you have to address the immediate problem. First off don't go back in the water till you get this corrected. If you can, go back to the shop where you got certified and see if they'll let you in the pool and work on your buoyancy.

You didn't give a lot of info but I'm going to assume you are diving cold with a 7mm wet suit 2 piece Farmer John, with hood, gloves and booties. As a REAL GENERAL rule of thumb for diving in fresh water figure 13% of your body weight for the amount of lead you'll need with an AL80. Like I said it's only a rule of thumb, I know a lot of divers who use a lot less. For salt water add a few more pounds. 30+ pounds seems like way too much given your story about having trouble ascending.

 

[Dive-aholic]

A lot of great advice already here. Overweighting along with the cold water exposure suit definitely sounds like the problem. This will get easier with practice. Once certified, focus on doing lots of shallow dives - less than 30ft/10m and working on your buoyancy. This is the hardest depth to maintain buoyancy, but once you master it there, you'll be good at all depths.

Lynne, great analogy!

 

[Blackwood]

i shot out of the water by about 2 feet

Nonsense.


In any case, practice your weighting, either in the shallows or in a pool. Try ascending and descending horizontally. It's much easier to control your depth.