What blows my mind is - I called DSS and they recommended for light setup warm water - 17lb winds with steel backplate. Which all makes sense - the way they added up neg and positive buoyancy. But the thing is I was diving cold water with a 3mm full suit and a 7mm shorty over it and 20lbs on the belt I could not swim to the bottom! no air in a scuba pro jacket bc ... Then I dove later with same setup but only a 7mm shorty with 23lbs and did fine. That kins of weight on a belt is a pain in the A**! What I am trying to do is shed the belt and weight - but dss was saying i might need 4 lbs at the most?? Am I missing something? Would the BC have that much negative buoyancy?
Ah, well for starters you never mentioned using anything other than a 3mm shortie,
You never provided any info regarding a 7mm suit.
As we discussed, if you add a lot more neoprene you will need a larger wing.
A typical 3mm full suit will be about 4-5 lbs positive. I'd guess a 7mm shortie could be 15 lbs positive, and most jacket type BC are inherently positive by 2-4 lbs due to foam padding.
3mm full suit ~ 5 lbs
7mm shortie ~15 lbs
Jacket BC ~4 lbs
Total 24 lbs
This is a *PERFECT* example of why I recommend actually testing the buoyancy of your exposure suit.
For the application you did describe, warm water in a 3mm suit with al 80's
Weight of your rig with a full tank:
Large SS plate and harness ~7 lbs
Regulator ~2 lbs
Full al 80 ~2 lbs
Rig max negative with a full tank -11 lbs
17 > 11 your rig will float if you ditch it
Your suit can only loose the buoyancy it starts with, 3mm suit ~5 lbs
17 > 5 the wing can *easily* compensate for the complete compression of your suit.
If your rig is -11 lbs with a full tank it will provide about 5 lbs of ballast with an empty tank. That's perfect if your suit is +5 lbs.
You *might* need 2-4 lbs in a belt, but I'd start with just the plate, reg and tank.
Tobin