VERY basic BC technique questions

[MauiScubaSteve]

The pike dive was in reference mainly for ocean dives.
Guess I jumped the gun.

There should be little difference between salt and fresh water dives; with the proper amount of weight for fresh it should be very similar as to with the proper amount of weight for salt.

Just don't go in overweighted.

Many, many divers dive with significantly more than "eye level, fully deflated, held normal breath, 500 psi tank" weight. Nearly every instructor/guide is carrying extra weight for students/clients, at least on the first dive with those divers. It is not that hard to dive overweighted, as long as it is distributed properly. It is much harder to dive with too little weight (for a normal breath 15', 500 psi safety stop). Even so I know of quite a few divers who do dive with too little weight for controlled neutral buoyancy at 15'/500psi. Mostly these are divers who never get their tanks under 1000 psi, swim down a lot and have a mooring line to hold at the SS.

Perhaps you are not quite far enough past the blind state to be leading the blind.

 

[knowone]

The pike dive was in reference mainly for ocean dives.
Guess I jumped the gun.
But you can still practice in a pool. You don't necessarily have to dive straight down, shallow angle dives work too.

Care to share your opinion in the matter?

In reference to what aquaregia said about surface diving. He's right, you should descend with your buddy, and stick with your buddy at all times. But if a surface dive is the only way to get you under, and you have the visibility to do so and see your buddy, you can do a surface dive and immediately revert yourself to be face to face w/ your buddy.
It's all personal preference how you get down. You could perform a kelp dive so you descend feet first and it would work the same way.

Just don't go in overweighted.

With the greatest of respect and humility, it is of my mind
that you could choose your threads and post wisely, and
listen and dive more, and speak less, which would have a
net result in the ability of eating more soup for all and sundry.

I would also hazard to proffer the same advice to myself.

 

[g1138]

To halemano.
When I deflate fully my eyes are under the water, if I exhale all the way I start to sink. But I don't like exhaling fully to sink feet first. So I breathe normally and do a shallow pike dive to get started. If I need to I reinvert myself to keep pace with my buddy.

There's suit compression too. Being in Monterey is not like being in Maui. I have a 7mm farmer john which puts 14mm of neoprene on my chest. When I descend it compresses, once I ascend it re-expands. For a 30ft and below dive, at about 3 feet on a low steel tank I have to keep myself finning at a slight downward angle to keep from poppinp up. Having said that, on shallow dives I go 20lbs VS 16lbs for deeper dives.

 

[g1138]

I'll think more before I post next time.
Thanks for the heads ups guys.

 

[TSandM]

web.boards, welcome to scuba diving! Be assured, you are not the only student who has found buoyancy in the pool to be a challenge. (Read the journal linked in my sig line . . . ) As someone has already stated, very shallow water is where buoyancy is most difficult to control, because the proportional pressure changes are very great. And to me, working with students, one of the biggest problems is that darned BC.

If you think about what the BC is FOR, a number of things will become clear. A BC is a buoyancy COMPENSATOR. What's it compensating for? The weight of the gas you intend to exhaust into the water, and any buoyancy from your exposure protection that you are going to lose from compression as you descend. If you are in a pool, using a small tank, and wearing a bathing suit, you have very little compensating to do. So, if you let enough air out of the BC to sink, it should only take a small puff to stop that sinking and make you neutral. When I do pool dives with students, I'll put one little squirt of air into my BC, and then I can swim back and forth from the shallow end to the deep end and back without ever putting any more in, or letting any out. I do that by controlling how deeply I breathe.

Most students want to do it by adding and subtracting gas from the BC, and that's hard, because your control isn't very precise. It's easy to overshoot and end up too buoyant and rising; then you let a lot of air out to avoid going up, and you sink. You become a "BC-induced yo-yo"! The key to stopping this is VERY small additions and subtractions of gas, and careful attention to a steady, rhythmic breathing pattern.

So the answers to your questions are: If you are floating up, you may be underweighted, but it's more likely that you aren't regulating your BC and your breathing properly. On descent, you can start adding gas to the BC as soon as you are fully underwater; doing so will keep you close to neutral on descent, which is a nice place to be if you have to stop because you can't clear your ears, or because your buddy is having a problem. There ARE dives where you want to descend fast, but they aren't beginner dives. And you never add gas to your BC on ascent, until your head breaks the water, and you want to float. An ascent should be started just by breathing a little deeper, and maybe swimming just a little bit up, and then you vent the BC regularly to keep yourself close to neutral -- again, it's a good idea to be able to stop an ascent any time you want. There may be a boat above you!

 

[RJP]

Perhaps the reason you need to pike dive is because you have not fully deflated your BC.

I find that an awful lot of students can't descend in some part because they are still unconsciously kicking to stay at the surface!

:shocked2:

It's such an ingrained action that they just can't stop.

A simple fix is to cross your ankles... and fully vent your BCD.

 

[MauiScubaSteve]

Perhaps the reason you need to pike dive is because you have not fully deflated your BC. Since we are 4-6 lbs negative, with a normal breath, at the beginning of the dive, if you fully exhale you should sink before you fully deflate. Then descending compresses both the air in the BC and the wet suit so you would get more and more negative as you get deeper. I often do not deflate at the surface and just haul myself down the mooring line. When I reach depth I still need to add air to my BC even starting with a fully inflated BC at the surface.

Another thing beginners do is remain vertical, squirm and twitch, which flexes the fins and pushes you up. I prefer to get the fins higher than my head and then squirming and twitching pushes down instead of up.

Let me say what halemano already said in a different way; I find that an awful lot of students can't descend in some part because they are still unconsciously kicking to stay at the surface!

:shocked2:

It's such an ingrained action that they just can't stop.

Another simple fix is to cross your ankles... and fully vent your BCD.

This is how I would have preferred that you use my words RJP.

 

[RJP]

This is how I would have preferred that you use my words RJP.

I would have had to have read them that far to have done so...

:cool2:

Either way, I was wanting to clearly make the distinction between "kicking" and "squirming and twitching" as I see most people with this issue quite specifically KICKING... not just an errant fin flick here and there.

 

[scubadiver888]

I am brand new to diving and am going through the process of getting certified.

Congratulations and welcome to the wonderful world of scuba diving.

I will not meet with my instructor again for another week, and in the meantime, have a couple of basic questions I'm hoping someone can help me with:

1. At various times while practicing in the pool, I found myself ascending without even realizing it. Does this mean I am not properly weighted? If so, is letting air out of my BC the main thing that I can do to not ascend without being able to get more weights?

Buoyancy is all about volume and weight. If the water your body displaces weights less than your body, you will sink. Things like lead weigh more than the water they displace, so they sink. A wetsuit is full of millions of tiny air pockets, so it is lighter than the water it displaces and it floats.

When you get in the water you want to have enough weight that you will sink when (a) your BCD is empty and (b) you exhale. If you have too much weight, you will need to add air to the BCD.

Now here is what happens when you go down... air compresses. The millions of tiny air pockets in a wetsuit will compress. The wetsuit will literally become smaller. Smaller volume but same weight means less buoyant. So as you go down and the wetsuit shrinks, you will start descending faster. Additionally, if you are wearing too much lead and had to put air in the BCD to compensate, the air in the BCD will shrink and you will start descending faster. If you had one cubic foot of air in the BCD at the surface, you will need two cubic feet of air at 33 feet deep.

So as you go down a small amount, you can use your lungs to increase your volume and control buoyancy. At some point, your lungs will not be able to compensate and you will add a small amount to your BCD.

As you come back up you need to do the reverse. As you go up, the air in the wetsuit and the BCD will expand and you will become more buoyant. At first, you can use your lungs to control your ascent rate. But at some point you will have to remove some of the air from your BCD.

Another reason you might be ascending without realizing it is if you are slightly buoyant, hold your head up or angle your body towards the surface, a gentle kick of the fins can send you up. If you are excited and breathing rapidly, this will increase your lung volume and you will go up. You need to exhale more to go down. Think calm, zen breathing.

2. When descending, at what point do you let air into your BC?

As I explained above, if the air in the wetsuit and the air in the BCD compress you will need to add air to the BCD. Note: the change from surface to 33 feet is larger than from 33 feet to 66 feet. So the first 10 feet is when your BCD and wetsuit will compress the most. This is the range that is hardest to control your buoyancy in.

It took me something like 20 dives to get everything going well. Not too much weight, calm breathing, not using my hands, not kicking when I didn't need to, being aware of body position, etc. I just worked on it one thing at a time.

3. While ascending at the end of a dive, at what point do you let air into your BC? While at the surface only?

Thank you for your patience.

Absolutely not only at the surface. When I am going up I try to be aware of how fast I am going up. If I stop kicking I like it so I start sinking. If I stop kicking for a moment and keep going up then I need to let air out of my BCD. If you wait until you feel yourself rising it could be too late.

If you have the correct weighting, at the start of the dive your BCD is almost empty. As you go down you VERY slowly add small spurts of air to the BCD. When coming back up you do the reverse, you VERY slowly dump small spurts of air from the BCD. You can do it a little faster than you added the air and compensate by kicking a little with your fins.

 

[MauiScubaSteve]

To halemano.
When I deflate fully my eyes are under the water, if I exhale all the way I start to sink. But I don't like exhaling fully to sink feet first. So I breathe normally and do a shallow pike dive to get started. If I need to I reinvert myself to keep pace with my buddy.

There's suit compression too. Being in Monterey is not like being in Maui. I have a 7mm farmer john which puts 14mm of neoprene on my chest. When I descend it compresses, once I ascend it re-expands. For a 30ft and below dive, at about 3 feet on a low steel tank I have to keep myself finning at a slight downward angle to keep from poppinp up. Having said that, on shallow dives I go 20lbs VS 16lbs for deeper dives.

The OP is "pool" practicing in an as yet undisclosed location, also with undisclosed tank and exposure protection; yet you think the OP "needs" to employ your personal preference for "kelp" descent wearing 7mm john/jack and using a steel tank.

I wear a 5 mm merino lined Pinnacle wet suit, and own two steel 120's; the weights I use, while less than what you use, are also used to compensate for suit compression, and air usage during the dive. The fact is that no matter your exposure protection, the base line recommendation for proper weighting (able to comfortably hold a 15' SS at ~500 psi) leaves you negative at the surface with a full tank, empty BC and normal breath.