Trim versus buoyancy

[Scuba]

MikeFerrara you wrote:

When you see a diver perfectly horizantal, knees bent and herdly moving their fins (a relaxed modified frog) yet moving faster than you and..hardly any bubbles being exhaled you will know what I mean.

Can you please explain the part about hardly any bubbles being exhaled. How is this indicative of a good diver.

I thought a long slow exhale was good. What I'm I missing here?

Peter

 

[Zept]

MikeFerrara once bubbled...
That is one of the advantages of the bp, it has weight and it puts it in the right spot.

...

In the tropics diving in just a swim suit the problem is reduced because you don't have much compression going on and never add much air to the bc. That is why some warm water divers with a jacket think they are doing ok.

Us tropical divers are doing the best we can, given the variables we have to work with. I know people who dive with only 2kg (4lb) of weight. I use 4kg (8lb), thanks to a generous layer of neoprene. It isn't practical for me to use a steel backplate or a steel tank, let alone both together. I'd certainly end up horizontal, but only because I'd be pinned to the bottom!

I know my gear would need a radical overhaul if I were going to dive in your cold quarries. Temperate diving is different from tropical diving, in some of its demands and constraints. Fair enough. However, I'm not going to go around beating myself up for not having cold-water diving skills when I don't have any cold water to dive in!

Cheers, Zept

 

[roakey]

Scuba once bubbled...
MikeFerrara you wrote:

When you see a diver perfectly horizantal, knees bent and herdly moving their fins (a relaxed modified frog) yet moving faster than you and..hardly any bubbles being exhaled you will know what I mean.

Can you please explain the part about hardly any bubbles being exhaled. How is this indicative of a good diver.

I thought a long slow exhale was good. What I'm I missing here?

Peter

I don't think he wasn't discussing breathing pattern, he was implying that good trim leads to less expended energy and less expended energy leads to less air consumption and slower breathing.

I'll even venture that good trim is the second most important characteristic that effects air consumption. You first slow your diving down so you’re not zipping around like the proverbial “puppy on a walk” -- that’ll be your most significant improvement. Trim comes next and then with various diminishing returns is making your gear hydrodynamic and better fitness (not to downplay those at all, however!).

I'm assuming here that the diver is not *horribly* out of shape.

Roak

 

[Uncle Pug]

... if this is a repeat then whack me over the head.

Many divers zip around like puppies out for a walk because the have crappy trim & buoyancy. They have to keep moving or they will sink (heads up folk) or rise (head down folk) if they stop. If they must stop then they immediately start in with the hand finning. They depend (without realizing it) upon water flowing over their bodies to provide lift to compensate for overweighting (or underweighting...which is the rare bird.)

First step is proper weighting.
Second step is proper placement of the weight.
Third step is proper trim.

 

[MikeS]

Uncle Pug,

Welcome back, I was beginning to think you’d been kidnapped by the BC Manufactures’ Guild or were being tortured to reveal the secrets of Pug Spit or that Shane had locked you in the fill station so he could play with your dive gear.

Uncle Pug once bubbled...
First step is proper weighting.
Second step is proper placement of the weight.
Third step is proper trim.

What is the difference between steps two and three? I thought that the proper placement of weight was the biggest factor in optimizing trim.

I think that everyone would agree that having good trim, defined by the ability to float effortlessly in any orientation, is a good thing. However I don’t remember trim being part of my PADI OW course and there seems to be some confusion, at least on my part, about the difference between trim and orientation (i.e. horizontal). The point of the thread was to confirm that what I was doing to adjust trim made sense and to see if there different and or better methods.

Mike,

While a bp/wings are in the long-range plans I’m not going to stop diving in the mean time. If I understand you correctly achieving good trim with a bp/wings is easier than with a BC. That being the case, everything I learn in theory and practice with the BC should apply to a bp/wings.

Thanks for the suggestion of the of the ankle weights on the tank valve. Since I have my own tanks now I have been marking the tank band location and noting the difference in trim as I move the tank up or down so I can fine-tune the location.

Thanks,
Mike

 

[MikeFerrara]

Scuba once bubbled...

Can you please explain the part about hardly any bubbles being exhaled. How is this indicative of a good diver.

I thought a long slow exhale was good. What I'm I missing here?

Peter [/B]

I meant that the diver is breathing in a slow relaxed fashion and not working very hard.

I should add that you should not intentionally breath less. This could lead to its own set of problems like Co2 build up. Gas usage is reduced as diving becomes easier and, of course fitness increased. I don't think reduced gas consumption should be the goal so much as a side benefit of overall good technique and fitness.

 

[Uncle Pug]

MikeS once bubbled...
What is the difference between steps two and three?

Step two has to come before step three.

But step two doesn't insure step three... as you have already noticed: moving the tank up or down in the bands has a huge effect...

What you may not have noticed is that you can effect trim by the way you hold your body... bend forward at the waist with knees dropped and head held high ~ or~ back lightly arched with knees held up and head down... this can alter your trim significantly.

Correct trim is actually more subtle than merely weighting.

Whilst weight placement is one element of trim that is easily seen and adjusted it is not by any means the only element and surprisingly not even the most important!

In fact many divers compensate for poor body trim by moving weights around... and actually end up causing problems of unbalance.

Paradoxically the diver who is always foot heavy/head high may need to move weight aft by positioning the tank lower. The reason the diver is in this attitude may be because they are holding themselves head high to keep from tipping over forward because they really are weight too heavy toward the head.

Here is an experiment I want you to try since you are having a foot heavy problem... before you move any weights around at all:

On the next dive hold yourself in what you feel is the correct horizontal position with knees up (just as if you were laying on the floor at home... in fact practice this position on the floor before you go out diving) and then I want you to tip your head down and look underneath and back... just your head... not your whole body... you should be able to see behind yourself this way.

If there is any tendency during this exercise to *fall* over onto your head or go inverted... you are weighted too heavy toward the head. Adding a weight to the tank neck is the opposite of what you need to do!

 

[MikeFerrara]

Good point. Compenstating for being top heavy results in a head up position. If you are foot heavy you end up head down to compensate. However if you are foot heavy and do not compensate you will go head up and vertical.

If you hover in a position as close to horazantal as possible (without needing to kick to maintain position)and end up head up you may be head heavy and if you need to be head down to hold position you may be foot heavy. It goes beack to having your centers of gravity and buoyancy in line. If they are in line vertically you will be stable horizantally (no apposing forces). When you compensate by tilting in the opposit direction than you are being pulled you are putting those centers in line vertically.

The relationship between weighting and technique and the effect it has on trim is the reason we can't take students out and have them trimmed perfect right off the bat. It's more of a process. You must get the weighting right to get the technique and you need the technique to get the weighting. So...you improve one then find that to go further you need to improve the other and so on. Even so, there are clues as to where the weight should go. Most should be in line with air bladder that will support it after your suit compresses and becomes less buoyant.

The lead wants to go down and the air wants to go up. If they are in line the equal but oposit forces cancel and there is no movement. If they are not in line, each will move until they are in line.

This explains why so many like a jacket at the surface. With a weight belt below and the bladder around the boddy above, it can do a great job of keeping you vertical at the surface with air in the bladder. The problem is that at depth ,when you must again put air in the bladder, the system will tend toward the vertical.

 

[MNScuba]

I use the ScubaPro Knighthawk which is a back inflate BC... I don't really see a problem with buoyancy or trim once I am below the surface. I hover effortlessly over and around objects once I establish neutral buoyancy. The only time I even think about the trim weight (if I don't use it) is when I am at the surface and have to fin to maintain an upward position. If I use my trim weights, this problem is almost non-existent. So, based on that I wonder if it has more to do with your bc or bp than the actual trim/buoyancy concerns you have.

 

[Uncle Pug]

MNScuba once bubbled...
I hover effortlessly over and around objects once I establish neutral buoyancy.

The real test of bouyancy, neurality, weight position, and trim...
Is to see if you can get horizontal and remain horizontal without any movement to compensate (hand / foot finning) while set maintaining depth.

The ultimate test of course is to do this with your eyes closed.

I play this game at the end of rec dives in 10 fsw.