Recently certified - buoyancy a mess. Would PPB help?

[inquis]

The "lever arm" is longer on the top band so less weight is needed to achieve a given shift in the overall center of mass. Trim pockets are usually limited capacity so being on top works well. However, if your smallest bricks are "too effective" on top, try them on the lower. (Slide the pockets up against the backplate to minimize any tendency to roll.)

 

[lowwall]

So it's rental gear and it has weight pockets attached on both bands holding the tank. Weight sitting on upper band vs lower band, how does it feel different? Does weight in upper tank band feel heavier/more balanced on the chest allowing the torso to come down for horizontal trim?

This explains why it's important to be horizontally trimmed:

Mastering Horizontal Diving Trim: An Effortless Balancing Act!

Horizontal diver trim is the foundation for good buoyancy control and efficient propulsion. It also helps conserve the marine environment.

scubatechphilippines.com

To achieve this you need your center of mass to be directly below your center of buoyancy when horizontal. People aren't naturally like this. Our legs are mostly muscle and bone which are negatively buoyant and our chest includes our lungs which is a big space with a bunch of air in it. That's why people's legs hang down when they relax in the water.

If all your weights are around your waist it will exacerbate this problem. Moving weight towards your head alleviates it. A steel backplate is an easy start to moving some weight forward. If it's not enough, trim weights on the upper band takes advantage of the additional lever arm from being a bit further forward.

A couple of years ago somebody came up with a good set of diagrams to illustrate all this. I tried to find them without success. Maybe someone can supply the link?

 

[Zinman]

The obvious one is to attach it lower. You've got a good 10cm left before you get to the sloping part at the top of the tank.

Next is check your harness. Use the crotch strap to control the plate height. You may need to loosen the shoulder straps to allow the plate to sit lower.

Actually do the plate height first. We can't see it directly, but from where the wing sits, it appears to be too high.

Thand you. The dive guide on the boat did my gear set up the 2nd time which is when this pic is from, and I didn't rechecking it cos he's a guide! It's a good point - I ll make it a point to recheck. Once you pointed it now, I can see it's quite low, which is not how I normally put it.

 

[Zinman]

Question - does it make you roll more if there's more weight lower down on the body?

The "lever arm" is longer on the top band so less weight is needed to achieve a given shift in the overall center of mass. Trim pockets are usually limited capacity so being on top works well. However, if your smallest bricks are "too effective" on top, try them on the lower. (Slide the pockets up against the backplate to minimize any tendency to roll.)

 

[Zinman]

This explains why it's important to be horizontally trimmed:

Mastering Horizontal Diving Trim: An Effortless Balancing Act!

Horizontal diver trim is the foundation for good buoyancy control and efficient propulsion. It also helps conserve the marine environment.

scubatechphilippines.com

To achieve this you need your center of mass to be directly below your center of buoyancy when horizontal. People aren't naturally like this. Our legs are mostly muscle and bone which are negatively buoyant and our chest includes our lungs which is a big space with a bunch of air in it. That's why people's legs hang down when they relax in the water.

If all your weights are around your waist it will exacerbate this problem. Moving weight towards your head alleviates it. A steel backplate is an easy start to moving some weight forward. If it's not enough, trim weights on the upper band takes advantage of the additional lever arm from being a bit further forward.

A couple of years ago somebody came up with a good set of diagrams to illustrate all this. I tried to find them without success. Maybe someone can supply the link?

Very good explanation.

 

[lowwall]

Question - does it make you roll more if there's more weight lower down on the body?

Weight in front that's balanced side to side should diminish a tendency to roll if you are face down and parallel to the bottom.

But I'm not the best person to comment on this. I started out as a swimmer and water polo player before getting into scuba. This means I more or less subconsciously compensate for minor disturbances to my trim without noticing it.

The only time I've felt a tendency to roll was on the initial descent of a dive the first couple of times I used HP120 tanks. These are quite negative when full and I didn't have any air in my wing, so when I tipped to one side to look around, it wanted to keep going over. It was easy enough to stop, but I could definitely feel it.

 

[steinbil]

This thread is a good example of why taking a course like GUE fundamentals early on is a good idea. There are many small equipment and setup issues that the OP is struggling with that would be easily fixed by a good instructor. Also learning a proper body position, buoyancy, finning and a proper weight check. There are so many obstacles to gaining comfort in the water if those issues are not addressed, so having more dives before the class would not be much help, and possibly would be a disadvantage because of bad habits formed. I feel lucky to have taken it early on, but I have heard from SO many divers that they wish they would have taken it sooner, because it made diving easier and more enjoyable.

 

[inquis]

Question - does it make you roll more if there's more weight lower down on the body?

If by "lower" you mean toward your feet, then no.

 

[FreqFlier]

Question - does it make you roll more if there's more weight lower down on the body?

It's obvious that OP lacks fundamental buoyancy/trim/weighting understandings.
Our comments may help a bit but may do more harm at the same time. I'd say to OP - find a decent instructor, get a dive or two in with him/her and you just may have your answers. Maybe fellow aussies can chime in?

 

[Cthippo]

It's obvious that OP lacks fundamental buoyancy/trim/weighting understandings.
Our comments may help a bit but may do more harm at the same time. I'd say to OP - find a decent instructor, get a dive or two in with him/her and you just may have your answers. Maybe fellow aussies can chime in?

I don't think those material is covered in most OW classes. I certainly was never taught how to compute or adjust weight, just told I needed about 28 pounds. The finwr points of distributing it for correct trim I learned from thos board.