What is proper procedure for downcurrent

[grazie42]

This is propably the best thread I´ve read on this board...

The problem as I see it (and as others have pointed out) with advice like "watch whitch way the bubbles go" and "deploy a liftbag" is that this requires the diver to be in "tv-mode" ie calmly and detachedly watching what is going on around him. For most (if not all), in a serious current, this will not be the case.

Currents certainly vary in appearance and caracter but what I think is necessary is a procedure that works in most currents (the solution that works more often then all others) differentiated on which way the current is heading (horisontal, up, down) and then to practise the procedure until you can do it without thinking. Papers I´ve read suggest that it takes about 10 000 reps to insert a response into muscle memory (which is the only place for any safety procedure in diving).

Is it rational to spend this much effort to (10 000 reps *3, in my example) to do this right? Do most divers even spend this much time practising other "more common emergency techniques" like rapid assents, lost reg, air sharing etc? Should we just accept that when we end up in a current we´ll have to figure it out then and hope it never happens? what do you think? (maybe this is a slight hijacking but I just dont see a consensus on procedure in sight)

 

[pufferfish]

Concensus, sure there is, I'm with Arctic Diver and DocV all the way

 

[Charlie99]

If at 66' we only have 1/3 the available lift, and 1/4 at 99', that means that my 40 lb wing will only provide about 13.3 lbs of lift at 66 fsw and 10 lbs at 99 fsw. In other words, if there is nothing to which hang on, and the bubbles are going down in a hurry, the BC might not have enough lift to get a diver out of the down current, so it will be better to just hang on and wait, gas supply permiting.

Huh? When fully inflated your wing has the same lift at any depth.

 

[Scubaguy62]

Huh? When fully inflated your wing has the same lift at any depth.

Ok...I remember reading about this, and it made sense considering the compression factor. I can't see how if the volume is reduced due to increased pressure the displacement will remain the same. Isn't displacement what buoys up an object? I don't mean to be argumentative Charlie, but I'd appreciate your view on this.

Semper Safe,

Rick

 

[ArcticDiver]

Concensus, sure there is, I'm with Arctic Diver and DocV all the way

Thanks for your affirmation.

But a previous poster is correct about using analogies to help explain. Using them in person is very useful. But, especially when there isn't a common background, they sometimes don't hit the mark.

To keep focused on the basic question: What should you do when caught in a downcurrent?

I think by now everyone agrees that first and foremost a diver should keep their cool. Let the mind run fast, not the body. Next, try finning away from the wall and up to steer out of the current.

If you can't steer out of the down current then inflate your BC. Then if the current hasn't let you go and inflating the BC hasn't had an effect start dropping weights sequentially. Drop sequentially to preserve as much ability as you can to have a controlled ascent.

It is the matter of inflating the BC that has brought the most confusion. It is hard to explain in a forum like this. I don't know what specific class Force and Vector Analysis is taught in nowdays. But it used to be in Jr. High Geometry and lower level H.S. Physics. So, maybe getting one of their text books would help in understanding.

That said let me take one more crack at helping those who don't understand. First, if a diver is going downward in a current and can't fin out of it they must do Something. What? Well they certainly can't hurt anything by inflating the BC. After all they already are going at the same speed as the down current. So, no matter how much surface area they present to the current it won't matter because they are already at equlibrium with the current. If they do nothing they are leaving their fate to the vagaries of the current. Maybe it will let them go, maybe not.

So, if the diver is already going as fast as the down current there is no way the current can cause the diver go any faster. So, what is there to gain or lose by inflating the BC? Gain: The diver now has the upward lift(bouyancy) of the BC working against the current flow. Loss: Nothing. The diver is already going as fast as the current. So, there is no extra energy to push the diver any faster. So, inflate the BC. It can only help.

Now, what about a horizontal current like when drift diving? In this case the BC's lift(bouyancy) is not going opposite to the horizontal current. It is going vertically at roughly a right angle to the current. So, will inflating the BC cause the diver to go faster? No, the diver is already going at the current's speed. The current can't push any faster. But the diver may go up when that is not the desired direction.

Up currents are another matter again. There it is important to do whatever possible to limit ascent rates. But lets' save that one for another thread.

 

[Scubaguy62]

Thanks for your affirmation.

But a previous poster is correct about using analogies to help explain. Using them in person is very useful. But, especially when there isn't a common background, they sometimes don't hit the mark.

To keep focused on the basic question: What should you do when caught in a downcurrent?

I think by now everyone agrees that first and foremost a diver should keep their cool. Let the mind run fast, not the body. Next, try finning away from the wall and up to steer out of the current.

If you can't steer out of the down current then inflate your BC. Then if the current hasn't let you go and inflating the BC hasn't had an effect start dropping weights sequentially. Drop sequentially to preserve as much ability as you can to have a controlled ascent.

It is the matter of inflating the BC that has brought the most confusion. It is hard to explain in a forum like this. I don't know what specific class Force and Vector Analysis is taught in nowdays. But it used to be in Jr. High Geometry and lower level H.S. Physics. So, maybe getting one of their text books would help in understanding.

That said let me take one more crack at helping those who don't understand. First, if a diver is going downward in a current and can't fin out of it they must do Something. What? Well they certainly can't hurt anything by inflating the BC. After all they already are going at the same speed as the down current. So, no matter how much surface area they present to the current it won't matter because they are already at equlibrium with the current. If they do nothing they are leaving their fate to the vagaries of the current. Maybe it will let them go, maybe not.

So, if the diver is already going as fast as the down current there is no way the current can cause the diver go any faster. So, what is there to gain or lose by inflating the BC? Gain: The diver now has the upward lift(bouyancy) of the BC working against the current flow. Loss: Nothing. The diver is already going as fast as the current. So, there is no extra energy to push the diver any faster. So, inflate the BC. It can only help.

Now, what about a horizontal current like when drift diving? In this case the BC's lift(bouyancy) is not going opposite to the horizontal current. It is going at vertical at roughly a right angle to the current. So, will inflating the BC cause the diver to go faster? No, the diver is already going at the current's speed. The current can't push any faster. But the diver may go up when that is not the desired direction.

Up currents are another matter again. There it is important to do whatever possible to limit ascent rates. But lets' save that one for another thread.

I'm sorry ArticDiver; I don't fully understand what you mean when you say sequentially. Should a diver take off his weight belt and drop a few weights and then re-position it? Should he take off one of his weight pockets and leave the other one on? What if he's diving without a weight belt or weight pocket, as some divers do?

Can't figure that one out. I seem to recall everyone else saying the same thing; Don't drop weights!!! But, as I've said before, I've never experienced a down current, despite having done several wall dives before, so again, in theory.

As far as the diver going at the same speed as the current with the wing inflated or deflated, the difference in speed may be so minuscule that it would be irrelevant to even notice it, so perhaps the airplane analogies were a bit extreme.

But it used to be in Jr. High Geometry and lower level H.S. Physics.

You might be right. I only took physics, college algebra, and advanced aerodynamics 20 yrs ago (notwithstanding a few thousand hrs jet time)...perhaps I should review the books.

Nevertheless, here is where I leave this alone. Just one question, and please, just food for thought; assuming there is a wind, when will a sail boat travel faster, before or after raising sail?

Semper Safe,

Rick

 

[ArcticDiver]

I'm sorry ArticDiver; I don't fully understand what you mean when you say sequentially. Should a diver take off his weight belt and drop a few weights and then re-position it? Should he take off one of his weight pockets and leave the other one on? What if he's diving without a weight belt or weight pocket, as some divers do?

Can't figure that one out. I seem to recall everyone else saying the same thing; Don't drop weights!!! But, as I've said before, I've never experienced a down current, despite having done several wall dives before, so again, in theory.

As far as the diver going at the same speed as the current with the wing inflated or deflated, the difference in speed may be so minuscule that it would be irrelevant to even notice it, so perhaps the airplane analogies were a bit extreme.



You might be right. I only took physics, college algebra, and advanced aerodynamics 20 yrs ago (notwithstanding a few thousand hrs jet time)...perhaps I should review the books.

Nevertheless, here is where I leave this alone. Just one question, and please, just food for thought; assuming there is a wind, when will a sail boat travel faster, before or after raising sail?

Semper Safe,

Rick

To answer a couple questions:

Sequentially: Means to ditch your weights a little at a time. If that means readjusting gear, so be it. If a person doesn't carry ditchable weights then I guess they can't use this method. But, I submit that such configuration, if weights are needed by the diver, is less than optimal. Some might even say unsafe.

Sailboat: What direction is the wind coming from? But, I'm reluctant to get off on another analogy track. We didn't do very well last time and only complicated the issue.

Cheers

 

[Scubaguy62]

To answer a couple questions:

Sequentially: Means to ditch your weights a little at a time. If that means readjusting gear, so be it. If a person doesn't carry ditchable weights then I guess they can't use this method. But, I submit that such configuration, if weights are needed by the diver, is less than optimal. Some might even say unsafe.

Sailboat: What direction is the wind coming from? But, I'm reluctant to get off on another analogy track. We didn't do very well last time and only complicated the issue.

Cheers

I know several tech divers (and even some recreational divers) who dive without weights because their rigs give them enough negative buoyancy to not need any.

As far as the sailboat, well presumably from the stern, but you're right...it's better not to go on another analogy track.

Dive hard, dive deep, dive lots, but for peak sake,

Semper Safe!

Rick

 

[Charlie99]

Ok...I remember reading about this, and it made sense considering the compression factor. I can't see how if the volume is reduced due to increased pressure the displacement will remain the same. Isn't displacement what buoys up an object? I don't mean to be argumentative Charlie, but I'd appreciate your view on this.

Let's say you have a 32 pound lift BC. It generates this lift by filling 1/2 cu foot of space with air. 1/2 cu ft of water weighs about 32 pounds. The 1/2 cu ft of air weighs about 1 ounce at the surface. 32 pounds - 1 oz = 32 pounds.

Inflate your BC on the surface. 32 pounds of lift.

Take your inflated BC to 99'. The 1/2 cu ft of air gets compressed to 1/4 the volume, and the lift is only 8 pounds.

Now push your inflator and fill up the bladder. Now you have 32 pounds - 4 oz = 32 pounds of lift (ignoring the tiny 3 ounce loss of buoyancy caused by higher density of air at 99').

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If you don't put in air, yes, you lose buoyancy as you go deep, but that's what we have inflators for.

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[Scubaguy62]

Let's say you have a 32 pound lift BC. It generates this lift by filling 1/2 cu foot of space with air. 1/2 cu ft of water weighs about 32 pounds. The 1/2 cu ft of air weighs about 1 ounce at the surface. 32 pounds - 1 oz = 32 pounds.

Inflate your BC on the surface. 32 pounds of lift.

Take your inflated BC to 99'. The 1/2 cu ft of air gets compressed to 1/4 the volume, and the lift is only 8 pounds.

Now push your inflator and fill up the bladder. Now you have 32 pounds - 4 oz = 32 pounds of lift (ignoring the tiny 3 ounce loss of buoyancy caused by higher density of air at 99').

----------------

If you don't put in air, yes, you lose buoyancy as you go deep, but that's what we have inflators for.

--------------

That makes perfect sense, but when you hit the power inflator at 99, wouldn't the over inflation protection mechanism kick in before the bladder was fully inflated?

Rick