what was up with this ascent?

[opalobsidian]

Hello!

I'm a new diver- I just did my 42nd dive yesterday with Thalassa Dive Center off of Bunaken Island, N Sulawesi (23 dives in 8 days!). So, while I learned alot on this trip, there are still many aspects of diving that I find baffling.

When I tried to ascend from this last dive, I was so suprised to look at my computer and see that I was going DOWN while finning UP! Everyone else was already on the surface but I seemed stuck at about 35 ft. If it hadn't been for my computer I would have had no idea what was going on as I had no frame of reference, just blue water all around, and tho I was trying my best to go up I was just bobbing around between 30-35 ft. Then, all of a sudden, I'd kind of shoot up all too fast, causing the computer to blink and honk. The DM was on the surface waving at me to come up, but all and all it took about 10 minutes to work my way up to a point of stabilization at about 10-12 ft so I could safety stop.

What the heck was THAT all about?

Pamela

 

[TeddyDiver]

I was so suprised to look at my computer and see that I was going DOWN while finning UP! Everyone else was already on the surface but I seemed stuck at about 35 ft. If it hadn't been for my computer I would have had no idea what was going on as I had no frame of reference, just blue water all around, and tho I was trying my best to go up I was just bobbing around between 30-35 ft. Then, all of a sudden, I'd kind of shoot up all too fast, causing the computer to blink and honk.

Looks like you were in a strong current dragging you down. Waters in Sulawesi are known of strong currents, and they migh be quite surpising how and when they change. You obviously hadn't any issues during the dive with bouancy before the accent so it wasn't any weighting issue?

 

[MikeFerrara]

Since no one else "got stuck" I don't knowif it would have been current.

It sounds like a buoyancy control issue combined with not having a visual reference. Ascents and descents are a couple of things that nmew divers have the most trouble with because of the way that it's taught (or not taught).

If you become negative you could certainly go down when you are kicking up. Without a visual reference ascents are always a little harder but start your ascent being neutral...take a bit more air into your lungs and you start up. Better yet stay horizontal and you can start your ascent by just arching your back a little to raise your head shjoulders (and lungs) a little which will start you on your way up.

If you dump too much you can still end up negative but being horizontal offers more resistance to up and down movement and the fluctuations won't be as dramatic.

To make matters worse many divers start out negative because of their head up trim...meaning that they must be negative to swim forward without also swimm up because they are always pointing up. As soon as they stop kicking forward they begine to sink. If they were taught to go vertical and dump air to start an ascent they end up with a tripple wammy. They are negative as soon as they stop swimming forward, they can sink even faster once they go vertical and then on top of that they are dumping air.

 

[diverdown247]

If you dump too much you can still end up negative but being horizontal offers more resistance to up and down movement and the fluctuations won't be as dramatic.
QUOTE]



Hmm.....can you say water displacement formula?? Great thought Mike. After 90 dives I hadn't even considered this type of ascent beginning. I always did a short fin pivot to get neutral, then took in a good deep breath to start my ascent.

 

[Santa]

Which site was it? I dived most of the sites around Bunaken several times - from Two-fish on the island though. If you dove off the mainland, where i believe Thalassa is I remember some pretty crazy currents coming down off the reef at the turn of the tide.

Also it was generally normal for the area for different layers of current to be moving in different directions and at different speeds - or for different currents to meet at corners and play hell with everything. The point of Bunaken - at the village - is especially bad that way. But it's just generally very unpredictable and sudden.

My bubbles would often just zigzag their way to the surface and I made a habit of keeping and eye out for how the fish and softcorals were moving around me.

 

[victor]

My 2c worth
Did you check you buoyancy on day 1 and always used the same weight every day?

After 23 dives in a short period of time you may well have ended up over weighted. I know I normally drop 2 or 3 lb's off the weight belt after a few days diving.
So following correct procedures before you started your ascent you dumped all your air from your BC.
Probably distracted and with no reference you started to sink, even though you were fining gently upwards.
After a few seconds you were down to 30 / 40 ft and very negative.
A little panic set in, you fin hard, but breathe shallow, you don't seem to get anywhere, it was a hard swim to get back to 15 ft, when every time the computer bleeps and you stop fining and you start to sink again.

How to avoid this happening again

Check you buoyancy every few days at the end of a dive with a nearly empty tank.
Don't worry about emptying your BC before you ascend, instead concentrate on being neutrally buoyant at what ever depth you currently are.
In open water watch your depth gauge every few seconds until you are sure you are neutral and controlling you depth on your breathing alone.
If there is an anchor rope stay near that as a point of reference.

:hai:

 

[MikeFerrara]

If you dump too much you can still end up negative but being horizontal offers more resistance to up and down movement and the fluctuations won't be as dramatic.

Hmm.....can you say water displacement formula?? Great thought Mike.

I'm not sure what you're getting at but...what moves through the water easier, a knife blade or a boat paddle?

Water displacement formula?

Archimedes' principle explains buoyancy but tells us nothing about hydrodynamics. Buoyancy is the force that propels an object up or down in the water column but there is drag/resistance to movement. When you are horizontal, you are more like the boat paddle than the knife blade in regard to up/down motion.

After 90 dives I hadn't even considered this type of ascent beginning. I always did a short fin pivot to get neutral, then took in a good deep breath to start my ascent.

Fin pivots might be useful in the pool to get a feel for what buoyancy control can do. Though we can argue that, it's pretty easy to come to the realization that there's no use for a fin pivot on a real dive. When you descend, you stop at the desired depth...before crashing the bottom. Then you swim around neutral. When and why would you doa fin pivot?

 

[opalobsidian]

Thanks, everyone! There's alot of great information here!

Yes indeed I was vertical and trying to kick straight up, gently circling, like I'd been taught to do. I've had problems before shooting to the surface too quickly, so not being able to get up at all was a bit of a shock!

Also, because I was wearing a 1 mm skin under my 5mm wetsuit, I was pretty well weighted (7 kilos in my BCD; I weigh 135 lbs) I was surprised how chilly the thermoclines could be!

I don't remember the name of the dive site; it was over where all the crazy spiky metal things are piled to help rebuild the reef where perhaps explosives had once been used for fishing. There's a big undersea memorial plaque as well.

Thanks again!
Pamela

 

[IceIce]

I think you might either overweight or there was a down current.
When you ready to ascend, you don't need to puff the BCD, but just let it and you will float to the surface, if you need some hard finning effort on every dive, most probably you have too much weight.
Down current could be the culprit, when you see bubbles blowing under rather than above you, the down current is there, be careful not to blow to the surface or being carried to the depth. When we were in Bali, the current tried to bring us down, when we hung on the rock, it turned direction and blew us to the surface, we had to abandon safety stop to avoid carried down again. It's quite impossible to do the safety stop too, as we had to fin and fight the current, which something like you've been through, going up but the gauge showing negative direction.

 

[victor]

Yes indeed I was vertical and trying to kick straight up, gently circling, like I'd been taught to do. I've had problems before shooting to the surface too quickly, so not being able to get up at all was a bit of a shock!

Also, because I was wearing a 1 mm skin under my 5mm wetsuit, I was pretty well weighted (7 kilos in my BCD; I weigh 135 lbs) I was surprised how chilly the thermoclines could be!
Pamela

The most likely thing is you were carying to much lead.
I suspect your tank was still at about 1000 psi, that many dives in a short space of time will improve your air consumption.
At only 135 lbs and a 5mm suit 7kg seems like quite a lot of lead, the skin adds no buoyancy. Maybe when you originally set your buoyancy you had some air trapped inside the suit.

On a dive trip it is a good idea to check for neutral buoyancy at the end of a dive every couple of days. I was amazed at how much less lead I needed after a weeks diving in warm water.