Another trim question....

[Scotty g]

And here it is...

Doing my AOW recently i was asked to descend to the 22m platform. Once i got there, i 'stood' on there (not kneeling) and felt as if i was being blown backwards with a light breeze (it was a quarry dive). I really found it difficult to stand upright on the platform without feeling i was about to fall backwards off the edge of the platform (my bouyancy was comfortably negative).

In another instance, i was happily swimming along at a very proud horizontal trim only to have to stop briefly to wait for my buddy.

If you can picture the scene (as if being to the left of me and the surface being at 12 o'clock), as i stopped, my trim was my head at 11 o'clock and my feet at 5 o'clock. Stopping in this position, i felt (then started to...) roll back so that my feet were now at 7-8 o'clock and my head slowly from 1-2 o'clock moving clockwise (basically backwards) so that i could feel myself ending up on the quarry floor lying on my tank. My tank at the time was a healthy 170 remaining.

Do i have to re-assess my configuration or do i have an unbalanced weighting problem? I'm hoping that this is just a practise issue

Scotty

 

[Charlie99]

It just sounds like your center of buoyancy is more to your front than is your center of mass. If you remain really and truly motionless, you will end up with your center of buoyancy directly above your center of mass.

The sort of situation you describe is most likely to happen if you have a relatively negatively buoyant steel tank, and/or a heavy steel backplate.

The first thing to try is to move the weights on your weightbelt so that they are as far forward (towards your bellybutton) as possible.

 

[TSandM]

If I'm reading your description correctly, I'm looking at you from the side. Horizontal would be head at nine, feet at three. You started out with head at eleven, feet at five. This is a long way out of horizontal trim, and suggests to me that you are carrying WAY too much weight low on your body. Are you using an integrated weight BC, with all your weight in the pockets? That will pretty much obligate a feet-down position whenever you stop finning.

When you stopped, you rotated even more feet down, and when you got to vertical, the negative buoyancy of your tank continued the process and you ended up tank down.

Frankly, I don't know what would happen if I tried to stand up with my rig on underwater. I can't imagine a circumstance where I would want to do that (unless I wanted to try moonwalking). But I certainly wouldn't be surprised if the tank would try to pull me over in that position.

It sounds to me as though you need to play with moving some weight up onto your back. You can use tank weights, or ankle weights wrapped around the valve, or weight pockets on the cambands, or, if your BC has them, trim pockets higher up on the BC to try to redistribute some weight and get rid of the feet-down tendency.

 

[Scotty g]

Hi TSandM,

Sorry i may not have made perfect sense the first time. I was head at 9, feet at 3 before-hand. My head at 11, feet at 5 was only when i stopped to wait for my buddy, i seemed to roll back more and more from there on in.

My weights were 10kg 'belt only' (not intergrated with BCD)

Lke you said, maybe i was wearing my tank a little low which made me roll back? Or maybe there was some other aspect in this? I look forward to hearing your thoughts.

Scotty

 

[Adobo]

Hi TSandM,

Sorry i may not have made perfect sense the first time. I was head at 9, feet at 3 before-hand. My head at 11, feet at 5 was only when i stopped to wait for my buddy, i seemed to roll back more and more from there on in.

My weights were 10kg 'belt only' (not intergrated with BCD)

Lke you said, maybe i was wearing my tank a little low which made me roll back? Or maybe there was some other aspect in this? I look forward to hearing your thoughts.

Scotty

Scotty,

It might be better to assess your trim when you are not moving. In other words, float at mid water and see if you can keep that horizontal trim without moving your arms or finning.

Here is an article written by an instructor in my area. The article is written in the context of a DIR diver (with the associated gear configuration) but really, the principles apply regardless of what gear you use. It goes into a lot of detail around the hows and whys. Pretty detailed but a good read.

http://forum.5thd-x.com/viewtopic.php?t=978

HTH

 

[TSandM]

The additional information makes me even more certain that my analysis is correct. You've got 22 pounds on a belt, which is low on your body. When you stop finning, your feet drop. This tells you that your static balance is faulty. Almost certainly, you need to move some weight up onto your back, using one of the methods I outlined above.

You might enjoy reading THIS article on static balance. It's much better than what I can write.

 

[GDCB]

I had the same thing happen once. I went from my AL 80 to a steel 72. I took 4ibs off my waist and became very back heavy. I then took the weight from my trim pockets instead and was balanced. Too much weight on my back made me topsy turvy. When weighted neutral front back I can swim and/or pause/hover in any position, rightside up upside down on my left or right side. All were required in my PPB class.

Lynn wrote "I can't imagine a circumstance where I would want to do that (unless I wanted to try moonwalking). " How about when taking a picture or doing a specific task. I think any position should be maintainable.

Carl

 

[Adobo]

The additional information makes me even more certain that my analysis is correct. You've got 22 pounds on a belt, which is low on your body. When you stop finning, your feet drop. This tells you that your static balance is faulty. Almost certainly, you need to move some weight up onto your back, using one of the methods I outlined above.

You might enjoy reading THIS article on static balance. It's much better than what I can write.

Beat you to it.

 

[Jason B]

Lynn wrote "I can't imagine a circumstance where I would want to do that (unless I wanted to try moonwalking). " How about when taking a picture or doing a specific task. I think any position should be maintainable.

Carl

What on earth are going to be doing that requires you to satand up while underwater?

 

[JeffG]

What on earth are going to be doing that requires you to satand up while underwater?

Maybe what he means is being vertical in the water column.