Now i'm just confused. I understand a SS backplate removes about 6 lbs but I need more than that.
The ultimate answer to where to put weight on a BP/W rig is 'it depends'
1.) It depends on HOW MUCH weight you need.
2.) It depends on where that weight is best placed from TRIM perspective.
3.) It depends on how much weight needs to be DITCHABLE
STEP 1: HOW MUCH WEIGHT
While it's true that you might need more than 6lbs currently, it's important to note that your current BCD is most likely positively buoyant itself. As much as 4lbs or more, depending on the model. So a switch to a BP/W rig that is ~6lbs negatively buoyant means a 10lb swing in how much lead you need to add.
Another factor that helps determine how much weight you'll need as you "transition to a BP/W rig" is whether you're transitioning tanks as well. Are we talking a single tank or doubles? And what kind of tanks? With a single AL80 you'll probably need some extra weight. With a set of steel doubles... maybe not.
STEP 2: WHERE TO PUT THE WEIGHT
Once you know how much weight you need, you need to figure out where to put it, starting with the impact on your trim. One of the benefits of a BP is that it puts the weight where the buoyancy is - where the wing and your lungs are located. This often helps improve people's trim significantly. Adding more weight from there should be done with an eye towards further refining - or at least not hurting - your trim.
For purposes of keeping discussion focused on "weight" let's assume you won't change anything else for now, let'd further assume that your trim is perfect with your new BP/W rig... but you need to add weight. Let's say 12lbs of lead, as an example
Well, you could put all of it on a weight belt, but that will move your center of buoyancy towards your feet and put you in a head-up situation. To help improve that, you could add a 6lb weighted tank adapter or bolt-on weights to your BP and 6lbs on a weight belt. This would help keep you in trim better as it would spread the weight out "north and south" if you will. Another option is to add weight pouches to your cam bands. The nice thing about that approach is you can move the weight to top or bottom cam strap, depending on where you need it for trim purposes.
STEP 3: HOW MUCH WEIGHT IS DITCHABLE
Just because you need to add weight doesn't mean that ALL of it needs to be ditchable. In the 12lb example above, having six lbs of ditchable weight should be more than sufficient in most cases... assuming you're properly weighted overall and diving a balanced rig.
Options for accomodating ditchable weight include:
- traditional weight belt
- weight harness such as DUI
- add-on weight pockets
DUI weight harness:
Add-on weight pouches are available from Halcyon, Dive-Rite, Hollis, and other manufacturers...