Uncontrolled descent

[tc]

Buoyancy CONTROL is important, a Southern California example- One of the most popular oil rigs off out coast sits in 700 some feet of water.

It would be better to control your descent and stop at the level you planned for your dive rather than hoping you can grab one of the cross braces they have every 60 feet or so.

If you were to have an equipment malfunction, like say- forgetting to connect your inflater hose, it would be much better to find this out as you were passing 20 feet rather than 120.

We have a name for those that use the bottom to stop their descent- Sand darts.

 

[Coldwater_Canuck]

May be possible, but seems rather unlikely. However, there's three main reasons I add air on the way down:
- by the time I can see the bottom, I don't want it to be "too late" and I crash into it (not the worst thing in the world, but not a great way to show off your bouyancy skills)

- if I get going too fast, I could do damage to my ears if I can't equalize on time

- holding down the inflator (as in if you forgot to add air on the way down) can help promote freeze-ups


Sometimes I forget to add air and then when I realize my speed picking up remember. But ideally I'll add it a little bit at a time so I sink at a nice pace

 

[Gilldiver]

I've never seen it myself - and I hope I never will - but uncontrolled descents do happen and can have calamitous results. I believe the nomenclature is "dirt dart". The increased water pressure and resultant compression will squeeze one's exposure suit into a second skin, so even the buoyancy of a thick suit offers little protection against what's happening. The increased pressure can also result in freeflowing regulators, burst sinuses/bloodvessels/eardrums, and induced vomiting and vertigo. Hopefully by then, one will have encountered the bottom and be in a physical and mental condition to extriacate oneself from the mess...but the odds are great.

We used the term "Dirt Dive" more often. The divers we saw do this tended to be more newer and very excited on a "big" wreck. They might have a full tool bag and large crow bar etc., say 20-30 pounds of tools. When they jumped off the boat with no air in the BC or dry suit, they just disapeared and we know we had a Oh ****! situation, as in the uncoltroled decent panic was a very possible result and we started to try to follow the bubbles. In many cases they poped up on the surface in less then 5 minutes and we had to swim out and get them. In 250+ feet of water this can be real bad.

As for suit compression, a wet suit will be fine as it compresses from both the inside and outside and you will keep all of your mobility, but a Dry suit will put a good squeeze on you. The squeeze can be so much that you just can not move quickly and may have a lot of movement problems period.

On the RMS Oregon I had my dry sut inflator pop off at about 30 feet - now this was in the 80's before I dove with both a dry sut and BC, I stoped on the bottom and had at most 50% of my normal mobility. By the time I got the inflator back on and some air in the suit I had some real pain from sut pinches all over my body. The bruse lines looked like a plate of spegetti all over my back and legs.

Jump off the boat with air in the BC and if you use it in the the dry suit till you know how this all works. and yes, there are guys who bomb a wreck in high current, but they may not be in a dry suit and have may have a scooter to help control the decent and "Landing."

 

[Rick Inman]

And then, there are those people that empty their wing and jump off the back of a boat with the trigger on a scooter pressed all the way down.

Sometimes it's fun to dive-bomb the bottom.

A couple years ago in Florida diving the The Lowrance (210') there was a ripping current, so the captain dropped us up-current with the goal being that we would lazily drop down and drift right into it. Well, either the current was faster than the captain thought or he dropped us a bit close, because it was quickly apparent that if we didn't start kicking madly for the bottom, we would fly right past the ship with the current.

I think that was the fastest drop I've made. Everyone managed to get to the ship, but most of us just barely made it, and several crashed into the hull when they hit. I have to admit, that was really fun. And since that dive, I've intentionally made the occasional dive-bomb descent. Sure, I've always had to madly add gas to wing and drysuit just before reaching depth, and I've had to equalize frequently on the drop, but otherwise, no problem. The goal has been to arrest the fall like Tom Cruse does when he drops on the wire in Mission Impossible.

 

[Davidstealey3]

And then, there are those people that empty their wing and jump off the back of a boat with the trigger on a scooter pressed all the way down.

not that i have seen that, but sure dont want to try it. we use a scotter for digging, but carry it down to the sand.

for the original question, when you did your open water class, did they not discuss controlled ascents and decents? and then talk about the importance of this. i know this is part of the SDI course, but cant comment on the other organizations.

you can decend as fast as you want as long as you can continue to equalize, but you are going to have to put air i your bc, drysuit or both to slow your decent at some point, and then to be neutral in the water too.

 

[fnfalman]

Dive bomb is fun if you know what you're doing. On one particular deep dive site (the USS Palawan artificial wreck outside of San Pedro, SoCal), its keel sits on 130-135 ft depth). I'd drop down slowly and equalize, then at around 20-ft, I'd point my head down, sweep back the arms and sky dive until I hit around 100-100 FSW, then I'd flare out (starfish the arms and legs) and start inflating the wing to slow the descend.

Primarily the people that sink like a rock to the bottom are newbies who were overweighted or experienced (which is different than skilled) people who never bothered to learn about proper weighting and buoyancy control.

 

[GrandpaScuba]

In 1995 I made my first warm water dive since 1982. I had under-estimated the amount of lead that I needed, but it wasn't apparent at the begining of the dive. But not too long into the dive, I realized that I was becoming too bouyant. In an effort to overcome the bouyancy, I went deeper, as I would if diving in Puget Sound. I finally got down to 80+ feet and was still bouyant, when it occured to me that I wasn't wearing a wetsuit, so there was nothing to compress by going deeper.

If you are not wearing a compressable suit and you don't have any appreciable amount of air in your BC, you should not become "more and more" negative as you decend. However, your decent rate may continue to increase (until terminal velocity, as some have pointed out) due strictly to momentum.

Controlling your decent rate is a skill you should have been introduced to in basic scuba. You should avoid a decent rate greater than 75 feet per minute. And I recommend that keeping your decent rate to 60 feet per minute or less is advisable.

 

[bigsnowdog]

My problem is not descending too fast, it is being barely able [and sometimes unable] to descend. If I am weighted in the average breath and empty BCD so I float with the water line at mid eyeball, I have a terrible time descending. I now have just over 20 dives. This is with an 8/7 mm hooded suit [we are diving in quarries in the midwest].

I find, if I check at the end of my best dives, during this weighting experimenting process, at the end of the dive, with the BCD empty and an average breath, my head is a foot or so beneath the surface. If I am weighted as you are supposed to be, at the end of a dive, as we approach the shore in reducing depth, once I get to about 8-10 feet I can't stay down. Too buoyant.

Once I get down far enough to compress the suit, then I descend fine. If I am not adding air to my BCD I will hit the bottom. The balance I want to achieve with respect to initial weight seems elusive.

I can start down, turn over and fin down, but that aggravates the ear equalizing thing, as it must happen quicker.

This is an interesting thread....

 

[Teamcasa]

There are several threads on how to do a proper buoyancy check but basically if you are unable to maintain a hover at the end of your dive, 500psi in the tank 8-10 deep, with zero air in your BC (and drysuit if used) then you need a little more weight.

I begin to add air when I descend as soon as I cross 15 fsw. Just a puff or two to my suit and BC. WHo knows, I might to stop and see something on the way down.

 

[Colliam7]

I believe the nomenclature is "dirt dart".

Five years ago, I was diving the U-352 off the NC coast. A large group was in line to drop off the boat, and my dive buddy was toward the end of the conga line while I was at the front. We did a pre-dive safety check at a distance with hand signals - very sloppy. He and I agreed that I would splash ahead and descend to the sub (bottom at 115') and wait for him rather than at the surface - it was a great day, good vis, no current - as we felt we were reasonably experienced divers and a decent buddy pair. I splashed and descended, and moved off to the side to wait for him to come down the descent line. A few minutes later I saw this ball of human limbs and dive gear dropping rapidly to the bottom, where it impacted in a huge cloud of silt. It turned out to be my buddy, who spent some time fiddling with his gear amidst the silt, before joining me. He said afterward that he realized as soon as he was in the water, and starting to descend, that he had forgot to connect his inflator hose, so he just let the descent go and enjoyed the ride. We still laugh about it.