Are we birds or submarines...

[scubajoh44]

This weekend I got caught in the crossfire of two people arguing over going to a deeper depth. Here are their arguments. (and they were really adamant about being right)

1. He said we should be like submarines and use our BC's to go up and down. He said this is how we make descents from the surface and how we should descend even deeper. It would be no big deal to maintain bouyancy even if we do this.

2. He said that we should be like birds and swim/"fly" down after our initial descent. He said that.. yes we would have to still maintain bouyancy, but that we are supposed to be flying not dropping.

I didn't think either of these was that big of a deal and told them it depends on the situation and the divers preference. They both attacked me then. They were set on being right. Thoughts????

 

[pants!]

I don't think either of them really have the idea.

The BC is not an elevator and it's not a ballast tank. It's a buoyancy compensator. The proper use of the BC is to compensate for your buoyancy changes.. ie, bring you closer to neutral. To descend (except from the surface where you begin positive), you should be exhaling, not removing air from the BC. It's kinda pointless to release air from the BC to descend when you're going to have to immediately put air back in to slow down and arrest the descent. A simple exhale is enough to get you to start 'dropping', and then the BC is used as intended.. you add air on the way down to control the descent, with each push of the button bringing you closer to neutral.

Same on ascent. An ascent should begin by taking a deeper than normal breath... it's pointless to put air in the BC that you're going to immediately vent to control the ascent. Again, in this method the BC is used as intended... each push of the vent button brings you closer to neutral.

I'm not a fan of swimming or flying downward either, as that's a lot of wasted energy.

 

[scubajoh44]

I don't know how the conversation even started. They just called me over and asked my opinion.....(big mistake for me to answer). I'de never really thought about it. It's just something that comes natural I guess.

 

[cfenton]

I don't think a diver should need to fin to go down or up; accept in an emergency. As far as a the BC it should be being inflated on the way down and vented on the way up. A change in lung volume is enough to begin an accent or decent and the bc should be used to keep it under control (i.e. venting on the way to the surface). Sinple right? So why the argument.

 

[scubajoh44]

Don't know.... That's why I was asking. Thought maybe I was missing something.

 

[theskull]

He was right. You were wrong. Go diving.

Excellent anwer, Pants! Those 2 paragraphs belong in the OW Divers Manual!!!

theskull

 

[Don Burke]

1. He said we should be like submarines and use our BC's to go up and down. He said this is how we make descents from the surface and how we should descend even deeper. It would be no big deal to maintain bouyancy even if we do this.

As a former submarine Diving Officer of the Watch, I can tell you that submarines use main ballast tanks to stay positive on the surface and vent off all of that air to submerge.

Barring some compelling reason, neutral buoyancy is maintained with variable ballast tanks and the ship is driven to various depths much like an airplane.

Bringing in a few tons of water to get deep from periscope depth or blowing main ballast to recover from a casualty is pretty much the extent of using weight changes to change depth.

 

[archman]

The very best OWSI I know has a saying that he repeats on almost every pool session.

"It's (inflator) NOT an elevator button!"

 

[Hammerhead]

To be fair, sometimes (strong currents when trying to hit a particular site on descent with no line for example), you need to fin to get there or miss it.

Equally, downdraft encountered on an ascent = fin upwards.

Having said that, it's always been a kick for me just to 'drop' almost immobile into the blue, without seeing the bottom until you get to the site.

Horses for courses etc...

Cheers,

 

[Wildcard]

If your swiming, your not diving. Float, suspend, hover, whatever you want to call it. Be like a cloud and just drift along. Want to go down? exhale. Up? reverse the last. Just an occasional burp of air in or out of the BC is all that should be needed.