Turned upside down

[waynel]

New diver, trying to learn. This past November my wife and I dove some chilly water and the dive op put us in 7 mm farmers (which means 14mm around torso) for the first time. We also used WI BC's for the first time. We had trouble getting down and I know that was because we didn't have enough weight. We fixed that but on the safety stop we both literally flipped upside down while holding onto the line! Our feet started started ascending until our heads were pointing down and our fins to the surface. It was struggle to maintain a grip on that line. Our BC's were totally emptied. What happened? We are totally confused about trim. Did getting rid of the weight belt and integrating weights into the BC leave us positively buoyant from the bottom of the BC down to our feet?

 

[divermatt]

were you using AL 80's???

 

[waynel]

Yes. Just as we did last summer in our 3/2 suits and belts.

 

[divermatt]

Well, AL 80's are usually +1 or +2 pounds towards the end of the dive, and keep in mind that wesuits have a variable boyancy--the deeper you go, the less boyant they are. So you don't notice that your tank is becoming positive, because at depth, your wetsuit is less boyant. When I was learning, I had the same experience that you did. As I surfaced, with my tank running low, I became more and more boyant, especially over the last 20 feet.

 

[Divedoggie]

Hi waynel,
The extra buoyancy of the thick neoprene combined with the weights in the weight integrated BC did change the dynamics of your trim. Your legs were indeed more buoyant, and the weights were above your center of mass. Thus your head sank and your feet lifted!

A weight belt is worn lower near your hips which is closer to your center of mass. You could have stayed in a horizontal position in the water more easily if your weights were distributed more evenly .

Many people use a weight system or harness when diving in cold water (with thick neo or drysuits) to distribute the weight more evenly.

You will get a myriad of answers here ranging from, think about using a backplate and wing system for buoyancy, to improper training.

It would be good to learn how to adjust your trim properly before you get into an open water situation. You can get into the pool with someone who knows, and get your weights distributed effectively, and find the proper amount of weight, at least for fresh water.
When you can hover in a horizontal position comfortably in the pool, you will be much happier in open water.

 

[sbrooks]

Did getting rid of the weight belt and integrating weights into the BC leave us positively buoyant from the bottom of the BC down to our feet?

No. You just didn't have enough weight if you had to hold onto the line to stay down - good thing there was a line. You are either positive, neutral, or negative. If you're negative but have buoyant feet (ie. drysuit inversion) then you'll be stuck upside down but still sink.

You just needed more weight - and if you're new - then a little more trim or buoyancy practice.

 

[waynel]

Well, We are leaving for Cozumel in one week to do 13 dives over six days. It's our first drift dives and as you know, no line for the safety stop. We are doing a shore dive when our great gets to the resort in the afternoon. I will certainly do a buoyancy check then, but do you suggest adding a little more weight (after the "eye level" check at the surface)? The last thing I want to do is to flip upside down and shoot for the surface on a safety stop. My wife is very concerned about this. We are new but we do have a couple dozen dives logged.

 

[Divedoggie]

You should only need a 3mm suit down there. Don't go overweighted. Do your eye level check at the surface.

 

[waynel]

We are cowards when it comes to cold. Believe it or not we are bringing 5 mil full suits for 78 water temp.

 

[Divedoggie]

Which dive op are you booked with?