Why so much weight (1st using 7mm suit)?

[spectrum]

So I'm getting the sense that new divers need more weight because even if we're breathing "calmly," we're keeping too much long volume even when we think we've exhaled? Perhaps because we're not quite comfortable yet, and we instintively hold on to some extra air?

That is true and you have all that nice fresh neoprene too.

Is the trick to good bouyancy not altering your lung volume over much, so that you don't have a huge difference between the inhale and exhale, while still using your oxygen efficiently? (I've done enough intro dives that I can calm myself down and not tear through my tank fast, but when trying bouyancy control in the pool, I still felt a lot of up and down between breaths.)

Deep breathing is the key to it. Some amount of porpoising as your lung volume swings is normal. One trick is to start your inhale just as you are about to sink then begin your exhale just as detect the start of an ascent. After a while timing and swimming technique can negate a lot of the up & down. For now be patient with yourself, relax and enjoy your dives. If you are self aware and dive with a spirit of continuous improvement a lot of this will come to you with frequent diving.

Deep, normal breathing is important to flush carbon dioxide from your body and to overcome the dead volume of your windpipe. If you are getting headaches odds are you are breathing too shallow.

Pete

 

[ianw2]

The pool, unless it is a very deep pool - 20+ feet - is a lousy place to play with buoyancy. In the top 15 feet of the water column, the smallest changes in gas volume create the largest changes in buoyancy. Physics again! At 16 feet of sea water (FSW), you've added half an atmosphere of pressure to your surroundings. At 33 FSW, you;ve doubled the pressure surrounding you that you had on the surrface. You won't double the pressure again until you hit 99FSW.

All this means is that, in the pool, small chnages in lung volume will cause large changes in buoyancy. At 33 FSW, the up and down will be significantly reduced.

If you were able to keep a constant volume of gas in your lungs, you'd be able to hover perfectly. That's exactly why those rat bastard rebreather divers hang there like they're pasted in place. The colume of gas intheir lungs, the loop and the counter lung doesn't change much.

Diving is Physics!

 

[LeadTurn_SD]

...Is the trick to good bouyancy not altering your lung volume over much, so that you don't have a huge difference between the inhale and exhale, while still using your oxygen efficiently? (I've done enough intro dives that I can calm myself down and not tear through my tank fast, but when trying bouyancy control in the pool, I still felt a lot of up and down between breaths.)

Thanks again, this board totally rocks -- I counted about 5-6 posts after only 15-20 minutes -- that's totally awesome!

Like with most everything else, the bouyancy control will come with practice and soon become second nature. You can use your lung volume to move up or down a few feet when needed without touching the BC inflator, but steady, deep, relaxed breathing is the way to go, both for bouyancy control and air consumption.

It is normal to move up and down slightly as you breath, but since it generally takes a couple seconds to start to rise or fall with changes in lung volume, you should not be moving very much.... if you ARE, you are probably pausing too long at the beginning and end of each breath. Think about how relaxed, deep and steady your breathing is during sleep. That is what you are striving for when you dive.

Your bouyancy will change as your depth changes, so you'll find yourself making small adjustments by adding or removing air from your BC. The key is to make the adjustments small.

Safe Diving!

 

[davidbaraff]

The pool, unless it is a very deep pool - 20+ feet - is a lousy place to play with buoyancy.

Diving is Physics!

You're right, of course. (The pool was only 12 feet deep, and I was doing the "lie on the bottom exercise.") I'll look forward to trying that again around 30-40' and see how I do!

We were playing around tossing a bowling ball around under water, and I thought it would be neat to try a "bounce" pass to my buddy, off the bottom of the pool. I was startled by just how loud of a noise it made when it hit -- almost painfully loud. Getting to experience some of the physics firsthand is, I must say, quite cool.

(I'd known about "inhale, rise up, exhale sink down" of course, and my background actually has a lot of physics in it, but it's still something else to *feel* these things firsthand, rather than read about them!! E.g. like feeling something have little apparent weight, due to bouancy, while still feeling the mass/inertia, when you try to slow it down.)

 

[Beachlover]

With the density of the water everything is quite loud.Just wait until you are out in the ocean and you try to determine the direction from which a noise is coming from.It's not easy to do.Anyway, just enjoy yourself and everything else will come to you in time.

 

[DwayneJ]

I have the same wet suit in XL size. I like dive with a Steel 120 and Al Backplate and am comfortable in the Ocean with 20lbs of weight. I also have a Steel backplate (+4lbs). On dive boats Al 80's and Steel backplate changes my buoyancy by up to an additional 4-6lbs and more with my Al backplate.

Alternating between Ocean and Fresh water confuses the issue somewhat. Ultimately your focus needs to be salt water buoyancy and the best thing you can do is spend 15 minutes hanging off the back of a boat adding weight until you find the right amount for you.