Descent rate

[Dan Gibson]

You don't have to tell me about current. I got my butt kicked in Little River last week doing a stage dive. The flow was higher than anytime I have been in there.

Beyond logistics, I am also refering to potential physiological problems associated with rapid compression. I'm not a doctor, so don't quote me, but I have been led to believe rapid compression can result in bone damage over the long run. It may be nothing most divers will experience unless they are involved in extensive commercial diving, but I just don't think it would be something I want to test.

I do know I have experienced alternoberic vertigo due to rapid descents on one or two occasions (both in cold water) and it trully wacked my vision and head for a moment or two. I didn't feel sick, but it wasn't the most pleasant feeling.

True - in most cases it is not the way to do it...But, I am referring to up current drops. There have been times where the current is ripping at a pretty good pace and we do a live / hot drop in full tech gear to hit a target at 150 to 170fsw. In a full tech rig, you do not have the best mobility and drag is very high in a current (Dry Suit, Double Steels, 2 Deco bottles, etc.) At depths like these, dpending on visibility, taking an extra 20, 30, or 40 seconds to hit the bottom may mean you miss the target. All depends on the scenario.

 

[dumpsterDiver]

Nope not with all the gear. If you do not have any gas in BC..... you sink like a mofo. And that is good, you want to be down ASAP in order not to miss the target. ....

I also do rapid free descents in currents to reach a wreck or something at depths over 150 ft. I will enter the water negative and swim straight down. Sometimes I will take a breath and exhale half of it and then not inhale for 30-40 feet to allow chest compression to aid in my descent rate. However, at no time am I sinking like a "mofo".

I think that a diver should not become so negative that they can not stop their descent at any point by simply swimming up. I have had times where I clear fine on the surface, but for some reason at 20 -25 feet my ears will completely lock up. In a situtation like this, if you can not stop your descent IMMEDIATELY you can easily damage your ears. Hitting the inflator at this point will NOT begin to stop a descent if you are very heavy and sinking; the inflator is just too slow if you are very heavy.

If I choose to, I can usually snorkel to a depth of 60 feet in less than 25 seconds and have no trouble clearing, but you never know when a tiny little piece of snot can ruin your whole day. Doing a very negatively bouyant descent without a descent line or wall to hold is dangerous.

We usually splash in 500 to 750 feet upstream of our target if the current is like 3 or more knots rather than being overweighted. If the depth is like 100, we might drop 300-350 feet upstream if the current is strong. Getting a "good drop" from the captain and perfecting a vertical descent seems safer than being too heavy.

 

[CD_in_Chitown]

Getting a "good drop" from the captain ....

There is the variable in that equation.

 

[PaulChristenson]

The 90fsw/min maximum descent rate shown there is for a very specific table. That specific table also has a limitation of 3 hour minimum SI. I wouldn't call that table a "standard".

I didn't say it was a standard...

Just passing on another Bruce special...

 

[IwakuniDiver]

After creating a few of my own underwater "mushroom clouds" on the bottom I came to this conclusion as my own personal standard for decents.

"Decend as only as fast as what is safe for your conditions."

I can clear my ears very rapidly and I know I'm capable of decending well in excess of 60fpm. On the occasional treat that I get to spash in an area with over 30ft of vis, I'll do just that, especially if a current is present. However, decending at night, in 5ft of vis, 60fpm will inevitably result in the creation of what has become affectionately known in my dive group as "The Great Cloud of Scott" and a good extra 30 minutes of cleaning out my gear back at the locker.

 

[CD_in_Chitown]

"Decend as only as fast as what is safe for your conditions."

A good plan, starting every dive with a mushroom cloud is a good way to pare down your dive buddy list.

 

[Bretagus]

Pardon my ignorance, but a "hot drop" is when you (and your buddy/group) enter the water negative (or enter and immediately decend), right?

I decend a little slower than my ears allow, as I find going too fast gives me a bit of a headache (sinus equalization?)

 

[IwakuniDiver]

A good plan, starting every dive with a mushroom cloud is a good way to pare down your dive buddy list.

I agree. It's a good thing that my buddies are more closest friends so the worst "punishment" I got was a rather clever label and I had to buy rounds after the first couple dives we went on. At least it still provides some entertaining beer-time discussions.

 

[CD_in_Chitown]

I agree. It's a good thing that my buddies are more closest friends so the worst "punishment" I got was a rather clever label and I had to buy rounds after the first couple dives we went on.

You're still figuring out the whole kit, I know guys with 100s of dives that descend that way. No personal insult intended, as long as the goal is to someday stop before impact on a regular basis.

Pardon my ignorance, but a "hot drop" is when you (and your buddy/group) enter the water negative (or enter and immediately decend), right?

I think a true "hot drop" is from a live/idling boat and the point is to get to the bottom before the current carries you past the target. Hitting a wreck from 150+ feet is part science part artform.

Straight Descents (or another term may be in vogue) involve stepping off a moored boat negatively buoyant and descending to 10-15 ft, finding the downline and buddying up to do S-drills and start the dive. This is the method we use in cold water to avoid breathing on the regs above the surface.

 

[Skeeter1097]

My first two wreck dives, I messed th target. The third time we went hot 3.5 knots of current on top. 15 ft. from the bottom and 10 SEC. to spear. Landed dead on. Know that is the only way to dive in current but I am steel new at this.