hot descending

[Mako Mark]

the only negative effect of rapid descents apart from the obvious equalization and buddy contact issues is soemthing called

Diabaticosteoarthuralgia.

basically the sudden rush of nitrogen disolving into the liquid that lubricates the joints causes some kind of super osmotic effect resulting in discomfort to mild pain in the joints.

I get it when I dive deeper than about 30-40m and do the "drop like a stone" descent.

Rapid descents also seems to increase narcosis a little.

 

[Rick Inman]

...and the faster you fall, the faster you'll have to decelerate so you don't crash into the bottom causing damage and/or silt-out.

 

[DA Aquamaster]

...and the faster you fall, the faster you'll have to decelerate so you don't crash into the bottom causing damage and/or silt-out.

In cold water this can be a serious consideration as a lot of gas will need to be dumped into the dry suit and/or wing in a relatively short period of time to achieve neutral bouyancy before impacting the bottom. With experience and a good feel for bouyancy and inflation rates this can be done accurately, but it places a high adibatic cooling load on the regulator and a first stage freeze up can result if the first stage is not environmentally sealed.

 

[Greg D.]

I personally like a fast deccent, closest thing you can get to a freefall in water

 

[eponym]

I'd like to know why is this a good or bad practice since I was able to control the equalizing of my ears and felt no bad effects.

While no-one in this thread has suggested finning to get down quickly, that might be poor practice. I’ll quote Dr.Deco from posts in 2002 and 2003:

September 2002, in reply to a post describing 100’+ wreck divers who “rocket down head first kicking the whole way”:

“[…] vigorously kicking to the bottom […] would probably do more to add tissue gas through the mechanism of increased blood flow to the body, especially the legs. This is not a theoretical concept; it has been known since the time of the physiologist Krough (about 1920). He received a Nobel Prize for his studies of blood flow and exercise.
Some increased blood flow continues for a while (about 20 minutes) even when you have stopped kicking. When you then make the ascent, you are generally less active than when descending (in this particular case). This arrangement could lead to potential DCS problems. I would recommend that vigorous activity to reach the bottom carries with it a potential penalty.”

August 2003:

“When one kicks to descend, the muscle pump is in activity and the heart rate is increased. When you reach bottom, the blood flow continues at a high level for several minutes (“post exercise excess oxygen consumption”). This will increase the gas loading beyond what would be expected from the algorithm. A later gentle, slow ascent to the surface will slow the circulatory system and the off loading will not be equal to the on gassing.”

I know that if I make a fast (but relaxed, non-finning) descent immediately on entering the water, I’m not taking a minute or two at the surface to relax after the exertion of gearing up and making my way to the exit. My heart rate is usually elevated when I first get in the water--especially around here, in the cold and the swell, but also in eager anticipation. Taking a minute or two on the surface to get back near resting heart rate makes sense to me, given the information from Dr.Deco. Nor would I want to skip my final in-water gear check and relaxing pre-descent visualizations.

As to the question of narcosis, here’s the Doc again, in August.2003:

“It is my understanding that nitrogen narcosis comes on very rapidly. This is because nitrogen is only slightly soluble, and it equilibrates very rapidly. […] Naturally, if you descend quickly to the 100 FSW level, you will experience the full effect of 100 FSW of nitrogen. If you descend more slowly, the effect will come on at a reduced rate since you are shallower. The final effect at 100 FSW will be the same […] irrespective of a fast or slow descent.”

But given Doc’s first quotes about elevated heart rate and increased gas loads, perhaps a rapid descent that’s done with an elevated heart rate can create more narcosis than a descent with low heart rate?

-Bryan

 

[Mako Mark]

As to the question of narcosis, here’s the Doc again, in August.2003:But given Doc’s first quotes about elevated heart rate and increased gas loads, perhaps a rapid descent that’s done with an elevated heart rate can create more narcosis than a descent with low heart rate?

-Bryan

good post Brian,

I think that most experienced divers know that the fastest way to the bottom does NOT include kicking down, it is the freefall.

Regarding the narcosis, I am sure that Doc is right about the net effect of narcosis being the same, but I think the sudden onset is what makes it more noticable and (although I hate using the alcohol analogy) you could compare it to taking a tequila shot compared to sipping a pint of beer. It has the same net effect due to the same dose, but one comes on faster.

 

[Uncle Pug]

I think that most experienced divers know that the fastest way to the bottom does NOT include kicking down, it is the freefall.

The fastest way is to let a scooter pull you down.

 

[Mako Mark]

(Note to self: Have both eardrums peirced, invest in modified turbopowered V8 scooter and take Rapid descents course with UP)

 

[Uncle Pug]

One hand for the scooter and one hand for the nose.

 

[Mako Mark]

One hand for the scooter and one hand for the nose.

So now I have taken the course, when do I get my card?.