Trim...

[wgw04024]

Hi, I don't know if this is a directly related to my bpw, but since that's what I have, I thought I'd start here first. My trim is heavy in the legs, and I'm not sure what my first move to correct it is. I'll use my example of a couple of weeks ago.

1. Bonaire.
2. No wetsuit.
3. Transplate with steel plate, with Voyager wing.
4. 80cf aluminum tanks.
5. 10 lbs of weight, 5 lbs on each side of my belt.

What is happening is when I'm moving along, even very slow, I am fine. However, when I stand still for very long (testing my trim for example), my feet start to drop and I start rolling backwards.

The one thing I did think of after returning home, was if a wetsuit might have more neoprene material in the top half, which would of helped out?

The trim isn't generally a problem except for I want to be able to hover without having to balance myself manually, and of course, taking a snap shot waiting for the right time is a pita.

Thoughts?
Thanks,
Bill

 

[snowdog61]

XSScuba trim pockets or something similar on the tank band (or a leg weight around the tank neck). Not sure what you are using for fins but something less negative will help (D6 Eddy fins are a bargain @$100). 10 lbs w/ a steel plate seems a bit overweighted for no wetsuit but if you've got your buoyancy right, trim is just moving around what you've got - but you knew that

 

[offfi]

Hi Bill,

I had this issue, too.
First of all:
Why did you dive with 10lbs even though you wore no suit?
I only used a rash guard (skin suit) during my last vacation. I was a little disappointed as I still needed 4lbs of weight with AL80s.
On most dives (deepest was 50m) my BC was completely empty.
The 2x2lbs were on my tank band.
Sometimes I still had the feeling my feet were sinking, even though they were the only part of my body with neoprene on.
This is where body tension comes in!
I often had trouble with my back, which I am sure now, is also a matter of proper tension.
After realizing this, I kept my back and thighs straight and as a result I maintained perfect trim.
Even the angle of the knees seemed to make a difference.

Hope this helps you somehow.

 

[Skulmoski]

If you are using flutter, try changing to frog kick. Bending at the knees brings weight forward.

Good luck

 

[rongoodman]

You don't say what kind of fins you're using it but lighter ones might help. Since we're in the Dive Rite forum, Dive Rite XTs are popular(Slipsteams and Deep6 Eddy fins too.). They're all light, and stiff enough to handle the frog/precision kicks. As previously mentioned, posture is a big part of it. If you let your legs sag, that's going to override whatever else you might try.

 

[lowflyer]

As mentioned, but also move your cylinder higher up on the BCD (toward your head) as much as you can without the valve banging into the back of your head with your neck extended.

 

[DevonDiver]

Steel backplate plus 10lbs and no wetsuit?

That's a very substantial amount of weight just to offset the weight of gas you consume and subsequent tank buoyancy (an AL80 becomes about 2.5lbs positive near-empty).

If you're overweighted, there'll be superfluous gas in your wing to lift that lead. Any slight deviation in trim will cause that gas to rise to the highest point. That'll swing you further out of trim.

Quite often trim problems stem from a flawed posture. Weak hips and dropping knees pull the whole lower body down. The best way to diagnose of you do this is by filming yourself with a GoPro.

There can also be some mental factors. If you were initially trained on your knees there can be an instinctive, unconscious, habit to drop the legs whenever you stop or do skills. Sounds absurd... but you'll dive how you trained. Breaking bad habits takes time and discipline.

Scuba Diving Skills On the Knees - Bad Habitual Response Conditioning

Trim weights are your last option, only once you've ruled out bad habits and weak skills.

The better alternative to adding trim weights is to consider the weight on your feet. Heavy fins... at the end of long levers (the legs) have a big effect. Get lighter fins... and if still leg heavy get some very buoyant booties - like 5mm hard soled (they're comfortable also).

 

[The Chairman]

As mentioned, but also move your cylinder higher up on the BCD (toward your head) as much as you can without the valve banging into the back of your head with your neck extended.

Negative. We are duped into thinking that we are moving our COG forward, but we're actually messing with COB: Center of Buoyancy. Put an aluminum tank in the water and you'll see the butt float up. This is accentuated as the air is consumed. Pushing the bubble as far back as possible will actually help to keep your legs up. Counter intuitive? Yes.

Attaching weights to the cam band or even the shoulders can help.

Do make sure that you're using the smallest amount of weight possible. I need a lot to sink my butt and I can't tell you how often people jump over me about how much weight I'm using. It's my naturally buoyant personality, I guess. So, figure it out, but the less weight you have to deal with the better.

 

[tbone1004]

@The Chairman the weight of the first stage and valve exceed that of the positive buoyancy of the tank. They do float tail up, but when you restrain the tank, moving the valve up towards the head has a greater impact on CoB than moving it down. Basic solids problem for moment arms around an axis. All of the negative buoyancy is concentrated at the valve and the first stage vs the positive buoyancy being evenly distributed along the length of the tank.
When the tank is strapped in, it becomes part of a rigid object and moving it towards your knees will not create a shift in CoB towards the head since the valve and first stage are moving towards the feet.

 

[lowflyer]

I'm not as experienced as most here, but this I do know in my own case.: I'm one who is leg heavy. If my weight isn't distributed well it is harder to maintain the posture alluded to by DevonDiver. So in my ignorant state I try to shift weight to maintain better posture. Secondly, if I'm feeling leg heavy and reach behind my back and push the tank, Al or steel, up toward my head, I stay more horizontal. Maybe I have it all screwed up and I'm anxious to learn, but that is what works for me.