What is proper procedure for downcurrent

[diverbrian]

Currents can be helpful if you use them to take you where you want to be. Down currents are currents. Therefore down currents can be helpful if you use them to take you where you want to be.

Best bet is not to fight any current but learn how to use the current to go where you want to go.

Of course a lot of folks don't get much practice in between vacation dive trips.

... the conditions that would cause a down dwelling on vacation. I have seen some "flagpole" type currents in the Great Lakes and some areas in Traverse City, but they are primarily NOT up and down. There aren't many walls where I dive to cause this type of issue.

This is all good information though and yes, it is better if you can use the current than if you have to try to swim perpendicular to it. Trying to swim against a strong current is definitely a waste of time and energy.

 

[Michael Schlink]

Rsoper, are you kidding?! That much work for a possible 5 minutes bottom time and the possibility of being swept away no matter who you are, sure sign me up, I'll let you know on my next trip thru-LOL-M

 

[ArcticDiver]

I have never dove anywhere with a down current and I was wondering what the proper procedure is for getting out of one? I would think that the best thing to do would be to swim horizontal out off the current rather than try and fight it and swim up. Similar to swimming perpendicular to the beach when you get caught in a riptide. Is this the correct plan?

This questions is in response to another thread regarding Nitrox and possible downcurrents.

Thanks,

TTSkipper

For whatever it is worth here is what I did on the two times I've been caught in downwellings and what happened. Both times I was diving on 29% EAN and they were drift/live boat dives.

Time one the top of the wall was at about 90' and the bottom was in excess of 1000'. The water went from the nice clear to that dark blue that looks more like ink than anything else. I at 90' on the top of the wall when I felt the downwelling and just swam away from the wall a few feet and it stopped. Actually no big deal. Then I ascended a bit, swam back over the more shallow sea floor and continued the dive.

In this case surface currents and sea state were mild.

Time 2 was again on a wall. But currents were high enough the captain had difficulty putting us in the correct place for the drop off. Top of the wall was at about 70'. I can't remember the sea floor depth but it was about 400 fathoms as I remember.

I swam around a coral head. In the time it took to make the swim around I was pushed down from the 70' to 155'. There wasn't a bloody thing I could do about it. Then the downwelling just dissipated and I was left with countering the resulting up elevator ride from the inflated BC. I dumped the BC and flared. My computer wailed mightily that I was going up too fast, just like it did on the way down as I passed the alarm depth.

But because I had not dumped my weights I was able to deflate the BC and stop the ascent fairly quickly. At this point I stopped, took inventory of all the pieces and parts, decided I was OK, decided to terminate the dive and started a slow ascent to 50' and then take my time getting to the surface.

So, my best advise from these two experiences is to first of all try to swim away from the wall. Second, if caught in it don't drop weights (you do have a BC with adequate size wings don't you?), then pay real close attention on the ascent so you don't injure yourself. Then, when all is under control terminate the dive and safely return to the surface before some other sea demon gets you

 

[Gary D.]

I hope this doesn't upset some of you but there are some things that for the most part you do not want to do.

Getting caught in a current can be fun if you stay relaxed, think about whats going on and then act. It's a shame that it isn't taught because so many people get exposed to current.

One of the last things you ever want to do is inflate a BC. That increases your surface area increasing the water pressure on your body making it harder to swim against or across.

Next time your in a car going down the freeway stick your hand out the window. Lay your hand flat and it cuts the wind. Put your palm into the wind and see the pressure difference. It will work the same way in the water only stronger by a bunch.

Think your going to stay in a real 3 knot current for 5 minutes? The Navy used to have current listed as 1.5 knots max for a working dive. 3 knots a "Navy diver" can hold his own in scuba. I have been around a lot of divers and very few and I mean very few civilian divers are in the physical condition to stay put in 3 knots let alone for 5 minutes and think about deco, air supply or anything else except staying in control.

We do a lot of current dives every year both for training and for real. What we do is called a "Ferry Swim". It takes practice and heads up on what your doing but it is swimming (above or below) across a fast moving body of water at an angle that actually assists you crossing without going down stream. To give you an idea as to how much current we can do that in the jet boat sometimes needs 2800-3000 rpm just to hold it's position. Max rpm's for the boat is 4800 rpm's.

MB talked about the Coz dive with the video's. I was on that trip and when the current first hit I was having a ball ridding it into and away from the reef as I filmed the current increasing.

The first few minutes was cool and I was having fun until I realized a lot of people were in trouble. Fun stopped and we got people to the reef and into a sand shoot. This is going to get some upset but when the current hit, the fins, other than plain old fashion single blades, needed help moving anywhere.

I was selfish on that dive because we just had two strong current training days just a couple of days before the trip to Coz and I was out there having fun not thinking about other divers who couldn't handle it. A lot of the group got bent and went for chamber rides but everyone made it home safely.

Think about what current can do before you expose yourself to it. It can be fun or it can be a death trap and how YOU handle it can make the difference.

Gary D.

 

[SDAnderson]

One of the last things you ever want to do is inflate a BC. That increases your surface area increasing the water pressure on your body making it harder to swim against or across.

Walter mentioned the same thing a few posts earlier. Obviously wing dynamics and lift capacity would factor into the equation, along with current speed and flow direction. Is there any math or testing behind this or is it an anecdotal thing? I certainly don't know where the balance is between the increased drag and the increased lift of inflating the wing, but I can see there there might be one at some point on the speed curve. Not that you're wrong, but it seems counter-intuitive (to me, anyway) that this would occur at anything less than a gale, or at least within the limits of my experience with currents. Do you know of any other information about this out there?

 

[Walter]

A good rule of thumb - when your exhaust bubbles are heading down, inflating the BC won't help.

 

[Gary D.]

Walter mentioned the same thing a few posts earlier. Obviously wing dynamics and lift capacity would factor into the equation, along with current speed and flow direction. Is there any math or testing behind this or is it an anecdotal thing? I certainly don't know where the balance is between the increased drag and the increased lift of inflating the wing, but I can see there there might be one at some point on the speed curve. Not that you're wrong, but it seems counter-intuitive (to me, anyway) that this would occur at anything less than a gale, or at least within the limits of my experience with currents. Do you know of any other information about this out there?

I don't know where the balance is either but I know like, Walter just said, If the bubbles are going down, What is a BC other than a contained bubble.

Another post says Inflate the BC but don't try a Lift Bag. Again Whats the difference? A bubble is a bubble.

On the Coz dive there was a bunch of divers. We had 2 boats just in our group. Some inflated at the very start of the current hitting and went up out of control. Others inflated later into it and went the other way.

The bottom line here is knowing how current reacts on your body and how to counteract those forces WITHOUT making a bigger bubble on your back that will most likely be counter productive. Lake and river currents DO NOT act like ocean curents and CAN NOT be treated the same. One is somewhat constant while the other is going to do ????

Bottom line. Be strong enough and have enough knowledge of the current AND your equipment to ride it out to safety.

Gary D.

 

[Charlie99]

I don't know where the balance is either but I know like, Walter just said, If the bubbles are going down, What is a BC other than a contained bubble.

The BC is a really BIG contained bubble. Not all bubbles rise at the same rate.

Another way to look at it is "what is a fastest possible ascent in still water ---- 1) swimming up full speed with BC deflated, or 2) swimming up full speed with BC fully inflated." I don't really know, and I don't intend to do the risky tests that would be needed to figure that out for my rig. Lacking any real info I'll just settle for " if the big bubbles are going down, don't inflate".

An often suggested technique for getting out of riptides is to swim at 45 degree angle to the beach. A 45 degree angle up and away from the wall might be a good way to hedge your bet rather than choosing to swim either just out, or just up.

Charlie

 

[ArcticDiver]

For this post let's break the currents into two different types: First, the original post, a Down Current. Second, a Horizontal (or nearly so) Current. In both currents what the diver is attempting to do is regain control by either overcoming or exiting the current's force. For this discussion I'm assuming the current is strong enough finning by itself is inadequate to do more than possibly steer.

In a Down Current one should inflate their BC completely and early. This provides the maximum up force available to counter the down force of the current. Finning is useful because in the process you might steer yourself out of the current.

Horizontal Currents are another matter. The BC's force vector (lift) is vertical up whereas the current's force vector is horizontal. So, inflating a BC will do nothing to counter the effect of the current. Nor will it help the diver steer. It might help the diver stay afloat if fatigued. Finning is useful because you might be able to steer yourself out of the current.

So to inflate or not to counter the current really is a function of the relative force vectors. How effective any escape method will be is a function of current strength and available lift for a Down Current and finning strength for a Horizontal Current.

As for the idea that inflating a BC is a bad idea because it just gives the current more surface to push on, well let's examine that for a minute. Once in a current the size of the object makes no difference in its' speed. The current will move all items at the same speed regardless of size. If you have a river nearby you can demonstrate this for yourself.

Gary, I'm with you, if you are in a horizontal current, which is what I think you were talking about, relax and play awhile!

 

[pufferfish]

Another place with notorius down dwellings is the Galapagos Islands. I don't remember offhand but four or five major ocean currents converge here hence the biodiversity and heavy current.

I have seen regulators ripped out of diver's mouths, fin clips undone, and masks come off in the current down there. I do remember one excellent DM Paula at Scuba Iguana who tells the story of being at 100 feet and getting caught in a down current. She initially tried swimming at an angle up and out of the current, but her bubbles were still going down so she started to inflate her BC. When you no longer can rely on the direction of your bubbles for orientation, and it is all deep blue around you the only way to know which way is up is to check your SPG. She did this and continued down until the BC's overpressure valves were releasing. At this point and I think I would have done the same she ditched her weight belt. Having an integrated system now I would likely just release a few pounds and see if I start to rise. In any case it wasn't until she dumped the weight belt that she was able to fin out and up from the current. She vented the BC on the way up and made an ascent and long safety stop without incident. The computer registered 210 ft and the whole episode took place in under a minute. Essentially a quick bounce dive. She told us this story so we would think about what to do in this situation.

Tell me in this situation without inflating your BC or dumping some weight how one might approach this? These down currents may be interfaces between Humbolt and Panama currents and just keep on going down well past depths I want to try swimming up from! If my bubbles are going down and my SPG needle is too then I'd start inflating rather than finning hard and getting tired. If that doesn't work then start dumping weight. I'd only start finning hard when I see that SPG depth stabilize in one place. Then I'd fin up and out at an angle while starting to dump air as needed.

To say never inflate a BC or dump weight are absolutes that may need to be broken in certain situations. Look at the rules for airplane cabin fires. Prior to the Swiss Air accident it was dump fuel waste time and then look for an airport. Now it is get the bird on the ground asap. Sometimes you just got to just trust your gut and break the 'rules' to live another day to tell the story. Paula if you are on SB thanks for yours