Bouyancy changes?

[boorens]

Hey Im new to this site, and cant seem to start my own forum. I have a simple question, and that its that I noticed that when I went for my first semi deep dive (35 ft fresh water, cold wearing a 7mil wet suit) in British Columbia, I expected a change in my buoyancy but it was much larger than expected. While it was a slow decent (painfully slow) from 0 to 20 feet, I seemed to drop extremely quickly at around 30 feet and was struggling to stop the descent much less rise back up to 30 feet (I dropped to about 45 feet before I could stop it. Adding that much air to my BCD in one go was un-nerving to say the least what with being taught not to take the "elevator" up constantly. does anyone have any tips that could ease my descent? I guess making little stops to make sure your in control every few feet? but it was pretty quick from 20 to 45.

 

[El Orans]

Hey Im new to this site, and cant seem to start my own forum.

I take it you mean "start my own thread"?

Consider it done.

 

[Charlie99]

The biggest changes in buoyancy are closest to the surface, so you changed buoyancy a lot more going from 0 to 20'.

I doubt that there was really any rapid change in buoyancy right around 30'. What is more likely is that you had been finning along with your body at an angle so your feet were down and finning was helping to hold you up. Then when you stopped or slowed your finning it appeared to be a buoyancy change.

There isn't any way to know at this point. Just keep it in mind next time.

Several times during your descent, stop finning completely and see if it affects your "buoyancy".

Of course, finning doesn't really affect your buoyancy, but it will cause you to ascend if you are finning upward rather than being completely horizontal.

 

[ScubaSteve]

My recommendation is to add air into your BC in short puffs rather than a large inflation at one time. Once you break the surface, breathe normal, equalize often and pay attention to your depth. Add a bit of air and drop, add some more air and drop. If at any point you stop dropping, then you are neutral (in a perfect world) or added too much air (as a newer diver this is more likely). Waiting until depth to add air into your BC is a difficult thing for a relatively new diver to do because it is so easy to overcompensate and hold the inflater button too long. Add less air more often and I think you will find neutral much easier.

Also, check your weight. If you drop too quickly it is also possible that you are overweighted....another common mistake with new divers. This will be easier to correct for as you get more comfortable in the water, but since the "dropping like a rock" syndrome makes you uncomfortable, it might help you now by slowing your descent and making you more comfortable.

This is of course just one man's opinion. You are going to get incredible suggestions and advice here (just Like Charlie's before me). There is a wealth of knowledge here and you have tapped it. Good for you and dive safe.

 

[diver 85]

Were you overweighted, how much weight and what kind of a tank did you use??.........I would try less weight next time if at all possible.......When I'm 2 lbs over it seems like I drop like a rock....good luck in your new adventures......

 

[Sinbad the Diver]

I had a major ah--ha experience this weekend taking deep classes, may be helpful.

I had been stuggling to start my descent and finaly got that part figured out (get that air out of your lungs and get yourself straight and still vertically). Once I got through that I was dropping like a stone until I hit bottom, in this case the platform we were descending on. That is not going to work going forward so I made a concious effort to change my body position to horizontal once I hit about 20 ft and begin to put short puffs of air into my BC. It had the desired effect and I was able to arrest my descent about 3 ft above the platform, make minor changes to the air in my BC and hover. I moved off the side of the platform and concentrated on maintaining a good hover for the next 5 mins while the others in the class descended (one person was struggling).

This was probably the most valuable thing I have done since starting to dive from an enjoyment of my dives perspective. By concentrating on boyancy I was able to cross my arms and relax for the entire dive and my air consumption dropped dramatically. Same thing the other 3 dives this weekend and for the first time I was not the person who's air was the limiting factor on our bottom time . You will read a lot on this board about focusing on bouyancy....it's the real deal IMO.

 

[TSandM]

Sinbad, that's a wonderful story! Diving is SO much more fun when you figure out how to get truly neutral.

OP, remember that the air cells in your neoprene are compressing as you go down. The proportional pressure change between the surface and 30 feet is the greatest you'll experience -- pressure doubles, so the air cells in the neoprene are half their original size at 30 feet. As you descend and this is occurring, your descent will constantly accelerate, unless you add gas to your BC to compensate for the buoyancy you are losing. (That's one of the reasons they are called buoyancy compensators.)

You've already been given the solution. Add gas in tiny puffs to the BC as you get deeper (I try to do it each time I clear my ears). Unless there is strong current and some reason why I need to get to the bottom in a hurry, I try to do my whole descent without getting any further from neutral than I can stop with my breath. That way, if my buddy has problems with his descent and has to stop for some reason, I can easily stop and stay with him.

At first, this may be difficult for you, because many newer divers don't yet have a sense for how long they have to push the inflator button to get that "puff" of air. If you overdo it, you'll find yourself going back UP, and then dumping gas and having the sinking too fast problem again. But each time you dive, you'll get better at it.

 

[The Kraken]

I call that loss of buoyancy "The Neoprene Plunge".

That first experience with really thick neoprene giving up the gas can be quite an experience.

Once experienced, never forgotten.

Safe dives . . . . . . .
. . . safer ascents !!!

the K

 

[boorens]

Thanks for the responses, I will check my buoyancy every ten feet or so to make sure Im still neutral until I get the hang of it. As for weight, I wore 28 pounds (The same amount my dive master had to get on me to descend and no I wasnt breathing harsh I was having a good time.)
I think it was partly that "Neoprene Plunge" plus the quick descent in the first place. After all a 7 mil wetsuit compressesed more than my usual no suit dive. Anyways thanks again.

 

[boorens]

Oh one thing else, where I was diving the spring run-off had apparently just came in and so the vis was terrible, descending to 30 feet with no orientation other than a computer was new to me as well.