Weighting for tropical diving with SS BP/W

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I just discovered this thread and am reading it with great interest. I am 5’10” and am now hovering right around 190# (down from 235!) Since I “shrank” so much, my old X Lg vest type BCD is way too big, so I bought an aluminum Dive Rite Back Plate with Oxy Cheq wing. On my June trip to Nassau, I dove my old BCD with 10# of hard weights, but since the BP/W is heavier than the BCD, I’m figuring I’ll be able to get in a pool session to get close. Long and short of it, you guys are giving me ideas I need to get started. Thanks!
🐸
 
I'm around 200, 5'10", could afford to lose a few pounds (180 would be about right).

With an AL80, a 5 mil, SS BP/STA, neutral fins, I don't need any additional weight and I trim out nicely.
 
I'm 6' 190# and with my aluminum plate and 5mil wetsuit I add 8# of lead for salt water. Aluminum plate and 3mil wetsuit I add 4# of lead for salt water, anything less than a 3mil 0# of added lead.
 
Just a note. A person's overall weight has only a limited correlation with lead requirements. At least unless you know the body fat percentage as well. Body fat has a density of around .9 (g/cc), while everything else averages out to about 1.06.

So if we take a 100kg (220lb) person with 25% body fat, we get 75x.06=4.5kg negative and 25x.1=2.5kg positive. For a net of 1kg positive. But then we have to add in 2kg positive for the typical amount of air that is left in the lungs after a normal exhale, so 3kg (6.6 pounds) positive before taking into account your gear.

Edit: This is for fresh water. Seawater has a density of around 1.027 g/cc, so every pound/kilo of lean mass contributes .033 pounds/kilos of negative bouyancy and every pound/kilo of fat contributes .127 positive.

For @Green Frog . If all of the 45 pounds you lost was fat (congrats!), you should be able to remove 5.5 pounds of lead (in the ocean). Your aluminum plate will add just over 1 pound negative, so that's 6.5 you can take off. The unknown is how positively buoyant your old BCD was. You might not need any lead in the pool and I suspect you'll only need 2-4 pounds in the ocean, but I'd start with 6 pounds and do a weight check at your safety stop.
 
To low wall and others contributing so much to the conversation, thanks! As near as I can determine, the Al BP/W is about 1.5# heavier than my old vest-type BCD. I had already lost the weight before I went to Nassau, but I’m afraid I lost a fair amount of muscle mass along with the “stored energy” (to avoid using the “F word”!) so I think I should be able to look at about 4-6# and be in the ball park. ⚖️

I’m hoping to take an early Spring dive trip to the Keys so I can drive and take a big load of gear then hope to do a dock dive to tune up my weight and trim. The 2 XS Scuba trim pockets on the waist band and the 2 on my cam band on my tank will each hold a 5# hard weight (or smaller) so I could go with no weight up to 20#. I’m diving an old tri-lam skin that contributes minimal buoyancy, but if I add a shorty or a full 3mm suit, I’ll deal with that when it occurs. Basically I don’t like to dive in cold water though! 🥶

As a backup plan, I’ve rehabbed an old ScubaPro Accent to use if I have to abandon the BP/W for whatever reason. I do have plenty of hard weights for the trusty old weight belt. Luckily my SUV has room to haul all of it. 😎

Thanks again everybody!
Froggie 🐸
 
Hawaii is warmish water not warm water and I now use a 5mm full suit year around there and you will see guides there in 7/8mm in the winter. Current water temperature is 80F.

+1

I've been in Oahu/Maui 3 times around mid October, 3mm barely cut it. Water temps 74-79F. I don't have 5mm and felt like taking 7mm to Hawaii was a bit too much.

6'2", 225, 3mm, ALU Xdeep plate, neutral fins I needed about 6lbs in Hawaii

On a boat - especially when your weight attachment is somewhat tricky - put 2# extra just in case so you don't waste anybody's time on your first dive. It'll help you a lot (assuming Cathedrals is your first? :cool: )
 
I would rather have a long, narrow weight in my STA than normal lead weights zip-tied onto holes in my backplate:

 
Lead flashing is my preferred weighting system

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https://www.shearwater.com/products/swift/

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