How do I control my bouyancy and trim?

[gadget]

Safety note:

Breathing and buoyancy are related but remember never use your lungs as a BCD.

If swimming along and you want to rise over an object avoid the temptation to take a big breath and hold it so you will rise.

If you get caught in a rising current the possibility exists of lung over expansion injury.

Just something to keep in mind as it only takes as little as 3 ft of pressure change to cause an injury if the right/wrong conditions are met.

With that said the best buoyancy trick is dive, dive dive.

 

[roakey]

Originally posted by gadget
Safety note:

Breathing and buoyancy are related but remember never use your lungs as a BCD.

If swimming along and you want to rise over an object avoid the temptation to take a big breath and hold it so you will rise.

If you get caught in a rising current the possibility exists of lung over expansion injury.

gadget,

There's holding your breath and then there's holding your breath. If you hold your breath by closing the back of your throat (“glottis”?) you're right, you can suffer a lung over expansion injury.

If you hold your breath by keeping your throat open, but by pulling your diaphragm down and keeping it there, there’s no danger of an over expansion injury since gas can flow freely in and out of your lungs.

That said, except in rare cases I stay with what’s taught in OW and “keep breathing” but what I’ll do is breathe shallowly at the top or at the bottom of my lung volume if I have to ascend or descend, respectively. This is only for a short period of time to “get things moving” and then I can resume normal breathing. If I was correctly neutral, I’ll continue in the direction (up or down) that I started.

So at some level I have to disagree with you, you do use your lungs as a BC, but within some constraints.

Roak

 

[k4sdi]

Originally posted by GeekDiver
My bro-inlaw can glide an inch from the botom and can adjust for varius contures like he has an invisable force holding him just above the bottom.

Use the force Luke!!


Remember putting your hand out the window of the car and making an airplane outta your hand? Its kinda the same principle in the water. Aquadynamics I think, anyway, the point is, try to imagine your body like that hand out the window.
seeeee the hand, beeeee the hand,,,,,,,

uggg

Mark

 

[Uncle Pug]

Originally posted by budgy
I wear a dry suit and as far as trim is concerned I think I am a bit light in the feet. I have been considering getting ankle weights.

If you think that you are too light in the feet then you are most likely not. Don't use ankles weights unless you are into UW aerobics. Correct horizontal positioning will have you feeling like you are going over on your head until you get used to it. Most new drysuit divers are so worried about getting into an uncontrolled inverted ascent that they conspicuously drop their feet and/or knees through out the dive. As Roaky has already explained this causes an upward force to be generated when you swim that is usually counteracted by excessive weight. When you stop swimming you sink. Very inefficient!

When you are in the correct horizontal position you should be able to tuck your head down and see directly behind you.

Now another thing that will help your buoyancy control immensely... in fact I consider it THE key... keep as much gas out of your suit as possible. Use the proper undergarment to keep warm... use argon if you must... but keep at least a 20' squeeze on the suit. (Don't be like Nate & Christy though and take it to the extreme - 65' squeeze and suit hickies all over.)

Use your BC or Wing for buoyancy compensation.... use your breathing for buoyancy control. There should only be enough gas in your wing to get you neutral at depth. You can make adjustments of 10 fsw just by changing breathing patterns. For example: when Shane and I are ascending to our next deco stop I might be busy winding up the lift bag spool. I don't have a free hand to be playing with my wing dump... and I certainly don't want to be dealing with expanding gas in my suit! By keeping only the minimum gas in the suit and only what is needed to stay neutral in the wing I can ascend the ten feet to my next stop without overshooting just by controlling my breathing. Then when I am there and done with my task I can make sure any extra gas is out of my suit and let out just a little from the wing to be neutral while breathing off the top of my lung volume.. when I got to the stop I was breathing off the bottom of my lungs to keep from overshooting.

Make sense?

 

[GeekDiver]

Thanks to all on the input and is helping me make some since of it all.

As to some of the questions sorry it’s taken me so long to respond back. I dive wet and fresh water at this point. I have a 3mil wetsuit and 12 lbs weight, at 10 lbs I’m a bit light. I have been renting steel tanks.

I have a rear inflate BC. I have repositioned the weight pouch to the rear of the cumber ban close to the air cell. I have been using 4 lbs on ea. side plus 4 lbs in tank trim weight (2lbs each pouch) The trim weight is via a strap attached to my BC and goes around the tank between the upper and lower cam straps.

I had not thought that practicing fin pivots, my trim would be incorrect but makes sense. When I practice the fin pivots I tend to have a hard time keeping my fins planted. I dive w/USD blades and they sink so I might try and see about getting some donut or leg weights and try positioning them around the neck of the tank and remove the tank trim weight from the pouches. That should help me get a better idea on how my trim is. I try to vary only 1-2 ft by controlling the way I breathe. When I get out of wack I have to start over so as can get my breathing back in sync with my motions. I’ll have to try the penny bit or at least picking a spot on the bottom and trying to hover flat that makes a lot of sense.

As far as holding my breath to change depth. I’m only talking for minor changes and understand that you should either swim or use the BC and to never hold you breath, but is good to point out. If I take to long a breath or exhale to much, if I don’t keep that under control then you can’t just suddenly stop an accent or decent and could end up 3-4 ft different than you intend. That’s the skill I want to improve on. I want to dive Texas Flower Gardens in a few months and don’t want to have to stay 5-6 ft above the bottom out of fear that I will crash into the bottom. That’s the reason I need to improve on this.

Thanks to all, will keep up the practice.
GD
You can go on a good dive, but that doesn’t make you a good diver.

 

[Paul168341]

Sorry Guys, but I HAVE to mention it...

PADI Peak Performance Buoyancy!

*Ducks from all the rotted vegetation being thrown*

 

[GeekDiver]

Yep your right and would fit the bill. In two weeks I will be in Austin for AOW dives.

GD

 

[ScubyDoo]

Originally posted by Paul168341
PADI Peak Performance Buoyancy!

I agree. I took my course about a month ago. If you want good buoyancy skills I highly recommend it. I came out of that course with a lot of confidence in my buoyancy skills. Just need to work my trim out.

 

[Zept]

Originally posted by roakey
There's holding your breath and then there's holding your breath. If you hold your breath by closing the back of your throat (“glottis”?) you're right, you can suffer a lung over expansion injury.

If you hold your breath by keeping your throat open, but by pulling your diaphragm down and keeping it there, there’s no danger of an over expansion injury since gas can flow freely in and out of your lungs.

How do you tell the difference? I've read several comments like this, but I have no idea whether I'm holding my breath with my diaphragm or my throat (note: I am trying this at my desk, not in the water).

Z

 

[neil]

Originally posted by roakey

First off, think of fin pivots as a skill done with training wheels. If you can do fin pivots, your trim in the water is all wrong: you’re heads up/feet down.
Roak

Roakey,
Excellent response, thanks! One of my pet peeves is the fin pivot. The ONLY purpose for the fin pivot is to have the student see how their breathing affects buoyancy (and basic use of the BC). All safely in the shallow end. That's all. And just for a few minutes. It was never meant to be a practical skill. And if their feet go up, even better. When I teach a PADI course, the students are supposed to demo pivots in OW. What the hell for? If they complete the dive demonstrating decent trim and buoyancy control, that's all I need to see. I don't want them on the bottom anyway.
If you can get a newbie horizontal and neutral in 3 1/2 feet of water, the rest is cake.

Neil