Trim, Buoyancy and Arm Position

[Blackwood]

In a way I think it does play a part, Marc.

When divers are working on technical diving skills, one of the things they learn is to hover motionless in horizontal trim. That requires excellent trim and excellent buoyancy control.

Go out to a given depth and stick your legs straight out. You'll rotate up. Sure, you'll have a little gas expansion in your wing and suit due to it being slightly shallower in the water column, but you should be able to hold that depth regardless of your body position (i.e. "trim").

I can flap like a bird on a deco stop without significantly sinking or rising. Similarly I can move my hands from my default position to my sides, across my chest, etc. without losing vertical position (at least within my own buoyancy control envelope which may not be as tight as some ).

It seemed to me that the thought in the OP was that flailing arms/odd arm position causes poor buoyancy control, something I disagree with. If related at all, the flailing of arms is caused by poor buoyancy and body control, not the other way around. Maybe that was the point, but if so I'm slow in getting it


From a trim standpoint, it's really easy to compensate for arm position with leg position since they're heavier and longer (and thus have a greater affect on trim). Compensating for leg position with arm position is not nearly as effective.

 

[boulderjohn]

Go out to a given depth ...

I understand your point and don't disagree. I think we are just a little apart on semantics.

 

[Blackwood]

I understand your point and don't disagree. I think we are just a little apart on semantics.

Could be. In my lexicon, buoyancy is the sum of weight and buoyant forces whereas trim is body position which is affected by constituent weights and buoyant forces, but independent of their sum.

 

[Buoyant1]

Depending...with my drysuit my hands are usually in front of me, left hand holding my right wrist (right hand usually holding a light)

In my wetsuit, either as mentioned above, or behind my back, hands under the cylinder...not sure where that one came from, but on a long dive it's comfy!

 

[pir8]

I don't stay in any one position all the time but generally vary between these positions depending on what I'm doing at the time.

 

[TMHeimer]

Normally I cross arms at chest or stomach (unless holding goody bag, of course). Sometimes I just let them drift back and to my sides. If I find myself in warmer water (60F or above) but only have my 7 mil wetsuit, I wear the top only--In this case I put my arms out front to balance out my (VERY) negatively buoyant legs.

 

[synctek]

It seems to me that trim and buoyancy are mutually exclusive terms if you define them separately. But you have to establish neutral buoyancy in order to have a properly trimmed profile, otherwise your all over the place. likewise if a divers feet are 6 inches lower than the rest of his/her body, swimming and maintaining depth will be an issue. It almost seems like Step 1. Buoyancy
Step 2. Trim

Just my opinion.

 

[Chris12day]

Hands in front holding camara. If no camara, hands in back on bottom of tank.

Safe Diving

 

[TSandM]

I don't think flailing hands cause poor stability. I think, as I was taught, that they are symptomatic of poor stability. My Fundies instructor told me to view hand movement as a symptom -- if I were trying to do something with my hands, it was because I was trying to compensate for a motion I didn't want, whether that was rising, falling, or rotating. When you get your gear balanced, and have mastered good body posture, you no longer use your hands, because you don't need them.

I tend to dive with my arms relaxed, my elbows hanging below me, and my hands in front of me, because stretching my arms out straight in front of me is hard on my shoulders. I use that posture when I need to go through a very narrow area, or when I really want to nail my trim to within a degree -- lifting my arms makes me lift my thighs and knees, too. But I find it a difficult position to maintain for long periods, although I have dive buddies who seem to find it comfortable.

 

[vladimir]

Hands in front holding camara. If no camara, hands in back on bottom of tank.

Safe Diving

Yes, left hand on camera handle, right hand on shutter release. If no camera, left hand on edge of hammock, right hand on margarita.