Buoyancy changes from BCD to BPW

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I didn't try it, but would guess that my 3mm wetsuit is a few kg's buoyant. I....

I dropped one kg when I stopped wearing my 2 mil shorty as a point of comparison. A full 3 mil suit, twice that??
 
I dropped one kg when I stopped wearing my 2 mil shorty as a point of comparison. A full 3 mil suit, twice that??
Something like that. Hard to say from thousands of miles away and all that, but that's a good starting place.
 
So is this aerated waterated or both

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but at different times


Platey
 
I dive this backplate with no STA in warm salt water with no thermal protection and an AL80 and I'm probably about 1.5-2kg overweighted because I sink like a rock without added buoyancy. There's not much I could do about it besides wearing a skin suit or something. I don't really care though. I dive comfortably and have all the freedom of movement I want. I can swing my rig up from wherever at any point in the dive even with total BC failure.
Don't stress it too much. It sounds like you're going to be very close, if not right on the money.
 
I am currently diving with a BC and am considering switching to a BPW set up. I dive warm salt water, no neoprene just board shorts and a rashie. I now use 4.5 kg weight and am thinking of dropping a half kg. I am currently on a fat loss/muscle gain quest and expect that by the time I hit my targets, if I do lol, I should be able to drop a second half kilo.



My concern is that if I go to a stainless steal plate, I will not be able to add any trim weight without being over weighted. I have no problems now being neutral at 50 bar as I can pass between positive and negative with my lung capacity with my BCD empty. Currently I need to be lungs fuller to get positive so I am thinking of dropping the half kg so I return to being neutral at half full lungs.



How much buoyancy does an empty BCD have over an empty BPW? I am thinking that there is at least a couple kgs difference simply due to the size of the BCD over a BPW. That would mean that without any trim weight I would already be over-weighted with a steel BPW.



Travel weight is not a consideration for me. I live in a dive destination and will leave my gear at the dive shop between dives as they have secure storage and are only a few steps from the boat/shore entry point.When I go to a different dive destination, I will most likely drive and again leave my gear at the shop between dives.

I am thinking that if I go to 4 kg lead now with my BCD, that switching to an aluminum BP, I would be able to drop another 1.5 or 2 kgs for the difference in the buoyancy between the two rigs and just have 2 to 2.5 kgs lead.

You're overthinking. Get a backplate, dive it, see how it goes. If you have to add a little air to the wing to get neutral so be it. You will see greater benefits in terms of trim and streamlining.
 
https://www.shearwater.com/products/swift/

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