Rapid Descent Rate

[Edward3c]

I get that, and I understand the principal behind it.

My understanding was that while some air would need to be added at depth to maintain buoyancy, you should never be so over weight that the air is required to arrest the descent vs using kicks to arrest the descent and then air in the BCD to reduce the work of staying at the desired depth.

If I tried to arrest my descent by fin strokes I would crash into to the bottom or continue past the planned depth (on a wall). By the time I get down to, say, 25m my neoprene drysuit will have lost around 4kg of lift, add in the 3,600Lt of gas I carry and finning isn’t going to work. I add gas to the suit as needed all the way down, then add more as I approach the planned depth to stop gently.

Edit: The descent is done slightly head down so finning would only send me deeper. Your suggestion requires a diver to be vertical, i.e. head up.

 

[scubadada]

When I get in the water, I tend to dump all my wing gas and exhale and descend pretty fast. When I get to depth I add gas to the wing and level off. We always worry about rate of ascent for obvious reasons but is there an unsafe descent rate? The only thing I can think of is maybe higher chance of narcosis?

60 ft/min is the planning descent rate in Multideco. I make a negative entry and swim down doing drift diving in SE FL. Looking at my profiles, 60 ft/min is about right. I've never thought that is too fast. I'm lucky. I clear with no effort. I have the gas added to my BC down.

 

[rongoodman]

My understanding was that while some air would need to be added at depth to maintain buoyancy, you should never be so over weight that the air is required to arrest the descent vs using kicks to arrest the descent and then air in the BCD to reduce the work of staying at the desired

Why would you want to descend vertically, as opposed to flat or perhaps head down?

 

[lostsheep]

When I get in the water, I tend to dump all my wing gas and exhale and descend pretty fast. When I get to depth I add gas to the wing and level off. We always worry about rate of ascent for obvious reasons but is there an unsafe descent rate? The only thing I can think of is maybe higher chance of narcosis?

This is completely anecdotal so take it for what it’s worth; I seem to be one of those who is more susceptible to narcosis when I drop fast. It might just be that detecting the narcosis is harder when it comes on slowly but on fast descents when I first get down I really notice it. FWIW, I’m talking 28% and 130’, I dive Trimix for any deeper

 

[kinoons]

Why would you want to descend vertically, as opposed to flat or perhaps head down?

You can descend flat or head down and change orientation as you approach the desired depth, much like an aircraft approaching landing.

You also don’t have to be completely vertical, as swimming forward with a 20 deg or so pitch up can arrest a descent. Not efficient for any distance, but works to arrest a descent while getting buoyancy dialed in.

With this in mind - see my earlier post about opening my eyes to more efficient use of the BCD.

 

[GF99/99]

You can descend flat or head down and change orientation as you approach the desired depth, much like an aircraft approaching landing.

You also don’t have to be completely vertical, as swimming forward with a 20 deg or so pitch up can arrest a descent. Not efficient for any distance, but works to arrest a descent while getting buoyancy dialed in.

With this in mind - see my earlier post about opening my eyes to more efficient use of the BCD.

Why not just descend horizontal/slightly head down when you approach your desired depth inflate and that's it. There is no kicking up or down, changing orientation, swimming at a pitch, flapping around, etc.

Just keep it simple. I was always taught kicking is for going forward and backward. Wing is for going up and down. Yeah you can make minor depth adjustments by kicking but you should not be kicking to actually keep your self from crashing into the bottom or floating up.

 

[grf88]

This is completely anecdotal so take it for what it’s worth; I seem to be one of those who is more susceptible to narcosis when I drop fast. It might just be that detecting the narcosis is harder when it comes on slowly but on fast descents when I first get down I really notice it. FWIW, I’m talking 28% and 130’, I dive Trimix for any deeper

I have the same experience with fast descents.

 

[sunshower]

When I get in the water, I tend to dump all my wing gas and exhale and descend pretty fast. When I get to depth I add gas to the wing and level off. We always worry about rate of ascent for obvious reasons but is there an unsafe descent rate? The only thing I can think of is maybe higher chance of narcosis?

How about your teammate? Are they doing the same or are you ditching them on descent and hoping to meet up on the bottom?

 

[kinoons]

Why not just descend horizontal/slightly head down when you approach your desired depth inflate and that's it. There is no kicking up or down, changing orientation, swimming at a pitch, flapping around, etc.

Just keep it simple. I was always taught kicking is for going forward and backward. Wing is for going up and down. Yeah you can make minor depth adjustments by kicking but you should not be kicking to actually keep your self from crashing into the bottom or floating up.

As I said in my response - the same advice was given earlier in the thread and has caused me to rethink my technique as described in my initial posts.

 

[RyanT]

I suppose you can go too fast (ear issues or increased narc), but on S. Florida hot drops, you need to go fast. I did 120 fpm yesterday to hit the wreck.