Figuring new lead requirements when you’ve lost bioprene?

[Marie13]

I’ve lost 12 lbs over the winter and continue to lose. I now have to figure out my weighting again. Last time I dove my CCR with heavy undies was late October. I needed 26 lbs with one AL40 for dilout (Kiss Spirit). I’m switching to a pair of LP50s, which seems to take me down to 22lbs.

Now that I’m down 12 lbs of bioprene, how much less should I be able to shed?

 

[lexvil]

Try 2lb and adjust as needed, undies seem to matter more, for me, than body weight.

 

[johndiver999]

{Mod edit}

density of fat - Google Suche

www.google.com

I looked up the density of fat. It says it is 90% the density of water. So if that is correct then you eliminate 12 lbs of fat, you eliminate 1.2 lbs of buoyancy. Is that the basic physics, right?

 

[grantctobin]

density of fat - Google Suche

www.google.com

I looked up the density of fat. It says it is 90% the density of water. So if that is correct then you eliminate 12 lbs of fat, you eliminate 1.2 lbs of buoyancy. Is that the basic physics, right?

I'd be surprised if it's more than a pound from the weight loss. I'd expect 5 to 5.5 from the AL40 to LP50 switch given the extra first stage and jubilee band and boltsnap and buoyancy difference, less if we're comparing empty cylinders rather than full.

All estimates based on level of loft consistently dived, and most people reduce their carried weight from dive 1 on a CCR to dive 100.

 

[inquis]

New cyl - old cyl: 2*1.25 (LP50s) - 2.4 (AL40) = +0.1 lb buoyancy (increase)
Losing 12 lb of fat translates to 1.3 lb lost buoyancy, based on the density of 0.9 g/cm3. However, you may have lost more than 12 lb fat and gained back muscle, which would make that -1.3 lb figure more negative. Bounding the problem with a max of 20 lb fat loss & 8 lb muscle gain, that's a buoyancy change of -2.7 lb.

In short, drop a minimum of 1.25 lb lead and a max of about 2.5... or just try 2 lb as @lexvil mentioned and see how you get on.

Edit: @grantctobin correctly points out there's another first stage & rigging, which would make you another 2-2.5 lb less buoyant. So I would guess you can drop about 4 lbs of lead.

 

[lexvil]

just like Marie, playful…

other times

 

[lexvil]

I hope the sea otters don't pick up on this trait...

They just look at you, like “ugly, to big to eat…but I may just Bash it with my rock”

 

[wetb4igetinthewater]

I need to find that pic where I stuck out my fist and had a juvenile steller sea lion bite down on it. I posted it online with the caption "This is what I do with impolite sea lions!".

I didn't kick a hornet's nest with that joke, but dozens of hornet's nests. I'll point out I was in heavy undergarments and additional layers and in a crushed neoprene drysuit. There's no punching by me, especially of an agile mammal that could bite a chunk out of me if it wished.

Anyway, this is a legit question. If I understand correctly @Marie13 is asking advice on a ballpark amount of weight to shed. My advice is to figure out two numbers for dry suit divers:
1) how negative is one's kit with nearly empty cylinders? This can be determined with a fish scale and a rowboat or dock
2) how positive is one in just their fins and exposure protection.

Then add the negative number with the positive number and there is how much lead to use. Then test it at a safety stop. And of course, distribute it to achieve trim effortlessly.

 

[inquis]

how positive is one in just their fins and exposure protection

That's a little difficult for a drysuit. You need to be in trim and underwater to obtain the normal amount of air in the suit & undergarment loft (and therefore buoyancy). It's tough to do that without an air source, though a long hose at the side of a pool works.

Personally I'd rather do a real dive than a pool dive, so I just shoot a little light and find the pressure where I'm neutral with empty wing. The weight of the gas over and above the minimum/reserve level is the amount I'm short. (About 12.5 lbs per cf for air.) The dive is over at that point, obviously, but it's no problem to ascend on less than 12 cf of gas (which is when staying down by breathing shallow starts to be uncomfortable).

 

[wetb4igetinthewater]

That's a little difficult for a drysuit. You need to be in trim and underwater to obtain the normal amount of air in the suit & undergarment loft (and therefore buoyancy). It's tough to do that without an air source, though a long hose at the side of a pool works.

Bingo. Can be done offshore as well.

Personally I'd rather do a real dive than a pool dive, so I just shoot a little light and find the pressure where I'm neutral with empty wing. The weight of the gas over and above the minimum/reserve level is the amount I'm short. (About 12.5 lbs per cf for air.) The dive is over at that point, obviously, but it's no problem to ascend on less than 12 cf of gas (which is when staying down by breathing shallow starts to be uncomfortable).

The test ultimately comes at the safety stop at the end of the dive for the diver to determine how much to inflate their dry suit for comfort.