How about the two arguing give their advise as to what I should get.
In evaluating the responses, you may wish to give at least some weight to the relative breadth and depth of the experience of the individuals from whom advice may come (as with most things on SB). Just a thought.
I have been reading everything and only get confused.
I am curious. Are there particular technical areas of confusion about BP/W rigs? Or, is the confusion something akin to, 'What model of computer should I buy?', or more along the lines of 'Should I buy a Ford / Chevrolet / Nissan / Toyota, KIA (etc., etc.)?'
---------- Post added August 30th, 2015 at 03:29 AM ----------
Every time we rent we get different age wetsuit (different compression factors etc) and different BC's but all are vest style and we have sinking legs with those, so wrestling with buoyancy and trim at times . . . . We want back inflate for trim issues but no rentals for those.
Mark, one other thought, if you are still with us on the thread (and haven't moved on, waiting for the fighting to stop
): it is not uncommon to see comments about 'sinking legs', particularly from newer divers. I would caution you that simply changing to a back-inflation unit from a jacket BCD may not fully address the trim issues. The switch is a good idea, don't get me wrong. But, you can achieve great horizontal trim with both a back-inflation unit or a jacket, or you can fail to achieve it with either. A lot depends on weighting - the total amount you carry and the distribution of that weight.
Think about your physiologic center of lift (CoL). Where is it? Generally, it will be somewhere in your thorax, above your diaphragm and below your collarbone - i.e. your lungs. OK, for those of us who have spent a lifetime developing a reserve store of bioprene, we may have supplemental buoyancy / lift as well, but the center fundamentally remains the same. In fact, think about what we try to teach in dive training - i.e. control your position in the vertical water column with your breathing, NOT by adding / purging air from your BCD. When you strap on a BCD, whether jacket or BI, you functionally augment the existing center of lift, as the bladder generally sits in the same general area as your physiologic center of lift. Now, where is your center of gravity/weight when diving? For many, it is 'lower' than the CoL, it is at the waist line. When you wear a weight belt, or even with many weight-integrated BCDs, the center of gravity / weight is below the center of lift. In the water, the two try to align vertically, and that weight pulls your legs down, while your lungs raise your (upper) body. It is not that your legs are necessarily 'sinking', or 'heavy', or negatively buoyant (in a small number of cases that may be true, but not for the most part), you are simply seeing physics in action. The solution - move the two 'centers' closer together. Many BCDs today come with trim weight pockets, usually located higher on the BCD, and taking some weight off the waist and moving it 'up' to those pockets really helps. But, divers still are reluctant to move too much weight to those pockets (from their waist), for a variety of reasons, and the center of gravity remains misaligned with the center of lift.
One advantage of a hard (metal) backplate, is that it moves weight to a position where it is more directly aligned with the center of lift. Not only that, a SS backplate, with a simple web harness, and SS waist buckle and SS D-rings, is generally going to be negatively buoyant. In contrast, most fabric BCDs - be they jacket or back-inflation - are positively buoyant, which means you add more weight to your center of gravity to compensate, which only worsens the mis-alignment of lift with weight / gravity.
The point - don't expect the 'sinking legs' trim issue to necessarily disappear if you only switch from a floaty jacket BCD to a equally floaty back-inflation BCD. Changing your weight distribution is equally, and possibly more, important. (Another way to affect that weight distribution is to switch from a longer AL cylinder to a shorter steel cylinder, but that is a different topic.) I dive a jacket BCD at times (teaching) and a (metal) backplate at times. And, good horizontal trim is possible to achieve with both. But, I carry more weight with the jacket, and horizontal trim is easier to achieve if I take my weight belt off my waist and drape it across my shoulders - not suggesting you do that, only pointing out the importance of weight distribution. (In fact, I use that shift in weight distribution with students to emphasize the the notion of horizontal trim, but that is also a discussion for another venue.)
