Trim in Weight Integrated BC's

[mccabejc]

Could someone give me a short course in adjusting trim in a WI BC ? I mean in terms of location of weight versus center of gravity and center of buoyancy, etc.

I would think that you need to place weights based not only on trim but also in ditchable vs. non-ditchable. I've heard you should have about 60% of total as ditchable.

I would also think the that back/shoulder fixed weights would tend to make you nose heavy when horizontal, counteracting the part of the tank weight. And I assume that the front ditchable weights are pretty close to your center of gravity/buoyancy, so would be pretty neutral in terms of trim.

I suppose I could hop in the pool this weekend and start experimenting....

 

[fmw625]

I would also like some advice. I'm new to diving. Certified the last weekend in June. Trying to trim to help hovering, tend to be foot heavy when not moving. Only dive with 4 lbs. of lead in .5 mm diveskin and AL80. Use Aqua Lung Maverick weight intergrated BCD.

Any help would be appreciated.

Thanks in advance

 

[WillHarm]

I dive with 20# 16 dichable, 4 non. Iv got 2 2# in the pouch on the bottom tank band, centered on the band. I think my trim is fine. Thats me. I would also think it depends on your BC, and how the manufature has placed the pockets. Iv got a Zegal ranger. my 2... good luck

 

[WillHarm]

I would also like some advice. I'm new to diving. Certified the last weekend in June. Trying to trim to help hovering, tend to be foot heavy when not moving. Only dive with 4 lbs. of lead in .5 mm diveskin and AL80. Use Aqua Lung Maverick weight intergrated BCD

Id guess its you fins, some have positive, some have negative. I belive, and dont quote this, most BLACK are negative, and colored get more positive depending on color. Not sure where i pick that up, I dont think i made it up... :lick:

 

[fmw625]

Mine are black and negative.

 

[Charlie99]

Could someone give me a short course in adjusting trim in a WI BC ? I mean in terms of location of weight versus center of gravity and center of buoyancy, etc.
..........

I suppose I could hop in the pool this weekend and start experimenting....

The shortest course is to simply note that you won't know what your trim is until you stop finning and just hover.

The basics are pretty obvious:

If you tend to pitch nose down when motionless, then you have too much weight in your back shoulder pockets. If you go head, move more weight up there.

What you have for fins makes a difference, particularly since they are out on long lever arms. Some divers swear by having highly negatively buoyant fins on your feet, then adjusting your trim by foot position. I prefer to get it right without contortions.

----
Some more subtle observations:

Tank positioning has both the obvious effect of immediately changing trim, but also effects how your trim changes as you use up your air or other gas.

Ideally, you can position the tank centered over your body such that it doesn't change your trim whether full or empty. If you go from nose-down towards nose-up as the tank empties, then the tank is too high. This "change in trim" effect happens with both steel and aluminum tanks -- air weighs the same in both.

You need to get your overall weighting correct before working on the details of trim. If you have too much lead, then you will have excessive air in your BC or wing to become neutral. This air bubble will move around as you change pitch and roll. In most cases, this air bubble movement is adds to stability, but negatively impacts agility. If you roll rightside down, the air bubble will move towards your back left side and will keep you in that position. You will only really know what your true trim is if you have virtually no air in the BC.

Hop in the pool and start experimenting!

 

[MgicTwnger]

I suppose I could hop in the pool this weekend and start experimenting....

Yes.