Buoyancy / trim question.

Ceberon · Sep 19, 2003

I am looking at a rock wall in front of me. I am horizontal. I have perfect buoyancy so that if I hold my breath at the right time, I do not move at all (yes yes, no holding breath, but this is not my point).

If I wear my last weight (2#) on my tank valve, I slowly tip down headfirst so that I'm hanging (perfectly buoyant) upside down.

If I wear my last weight (2#) around my waist, I slowly tip down so my legs are hanging below me.

Am I correct that in the perfect world, I would be trim so that I would not tip in any specific direction when horizontal? So I'm assuming I should be moving my weights around until I fix this tipping problem? Any suggestions? I know if I swim even slightly, I don't have any problems, but I would prefer to be able to hang motionless.

So many people write about fixing their buoyancy, but that's never been my problem, I've had a lot more problems with trim.

yoda4x4 · Sep 19, 2003

I may not be an expert, not by any means. But why not try one of these:

putting only 1 pound at your waist,
or 1 pound at your waist and 1 pound at your tank valve,
or putting only 1 pound at your tank valve.

Sometimes trial and error is your friend.

David

Dan Gibson · Sep 19, 2003

You could do it the easy way and use your legs to lenthen or shorten the lever arm. As the air in your tanks is used, that alone will alter your trim. Placing a trim weight here or there won't cover you for the whole dive. This is why the cg drill is so important to learn.

yoda4x4 once bubbled...
I may not be an expert, not by any means. But why not try one of these:

putting only 1 pound at your waist,
or 1 pound at your waist and 1 pound at your tank valve,
or putting only 1 pound at your tank valve.

Sometimes trial and error is your friend.

David

Diver0001 · Sep 19, 2003

Ceberon once bubbled...
I am looking at a rock wall in front of me. I am horizontal. I have perfect buoyancy so that if I hold my breath at the right time, I do not move at all (yes yes, no holding breath, but this is not my point).

If I wear my last weight (2#) on my tank valve, I slowly tip down headfirst so that I'm hanging (perfectly buoyant) upside down.

If I wear my last weight (2#) around my waist, I slowly tip down so my legs are hanging below me.

Am I correct that in the perfect world, I would be trim so that I would not tip in any specific direction when horizontal? So I'm assuming I should be moving my weights around until I fix this tipping problem? Any suggestions? I know if I swim even slightly, I don't have any problems, but I would prefer to be able to hang motionless.

So many people write about fixing their buoyancy, but that's never been my problem, I've had a lot more problems with trim.

Does your BCD have weight pockets behind your shoulders?

R..

Ceberon · Sep 19, 2003

Actually this issue revolves around me just getting a new BCD (DR TPII). It's great, I like it a lot. Don't think it has weight pockets behind my shoulders, although that's something to think about.

I guess I was just wondering if there was anything not obvious that I wasn't thinking about. I know I did get down to around 600 lbs in my tank and it threw my trim off, but that's to be expected. I can move my weights around, as yoda said, one on the waist, one on the tank or something similar, I just wanted to make sure I had the right ideas

I keep hearing from people "Don't worry about the trim now, the gear is new, wait until you're used to the gear". I don't see how being used to the gear will change how I float when I'm not moving.. I'm not saying I'm uncomfortable, I'm just a perfectionist.

Charlie99 · Sep 19, 2003

Ceberon once bubbled...
.. I'm not saying I'm uncomfortable, I'm just a perfectionist.

If you are a perfectionist, another thing you can play around with the tank position so that whether the tank is empy or full, it doesn't affect your head up/ head down pitch. For example, if you go more head down with an empty tank, then move the tank higher up on your back.

It sounds like you are close enough on trim that just extending your legs vs bending at the knees will change your trim enough to be able to do motionless hover horizontally. You will also just unconsciously start bending your torso or arching your back a bit to adjust.

Ceberon · Sep 19, 2003

Thanks for the tank position suggestion, I did notice I was having a more feet first rise once I was running low on air.. hrm, I'll have to think about it.

herman · Sep 19, 2003

I get the impression you feel that you should be able to just "freeze" and stay perfectly horizonal. If you are neutral, the slightest thing can change your CG. When I took my DIR-F class, one of the things that was ask of the instuctors was " how do you keep horizonal and stay perfectly still?" These guys looked like they were laying on a rock, not moving at all. The answer suprised most of us. What we were told and later saw was that they CONSTANTLY made very very small changes in their legs and the arching of their back to keep things horizonal as well as very small movements in their fins. So, if these guys who have very good at trim and bouyancy control have to "tweek" their trim constantly, so should the rest of us.

Ceberon · Sep 19, 2003

Well, yes, I did have the impression you could hold perfectly still

Thanks for the suggestion. I can hold very still if I continue to twitch my fins once in awhile, move my arms down, or up, etc etc. I'll have to pay more attention when the instructors are holding still.

Thanks a ton. I'll still be taking more classes & learning more, but that should help me a lot when I'm doing my fun dives.. I like to try to improve something every dive, and that was really bothering me last weekend, since I kept moving my tank & weights around, and no matter where I put them, I always was drifting slightly in some direction..

bwerb · Sep 19, 2003

Think of it like steering a car. No one just holds the wheel completely locked in place on a straight road, there is a constant miro-adjustment of the steering wheel going on almost constantly to keep the car going straight.

Same with trim. Moving the two large levers you have forward and backward (arms and legs) in conjunction with your head position (look up vs look down) and minor fin sculling keeps your trim spot-on when you want to hover "motionless".

Buoyancy / trim question.

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