brian montecno
Registered
I've been looking for answers for some time now and desided I need to ask. I am 170# , I use al. bp/w is 30# venture and would like to be sure if that is enough lift using 30 stage and lp95.
Is 30# lift enough?
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More than enough with some left over. N
*Floater*
Contributor
it would be for me.
Plenty...
Unless your wearing around a hundred pounds of lead it is. 
Gary D.
Gary D.
KCIREVAM
Contributor
My question pertaining 2 lift. What is rule the of thumb when it deals with lift lbs? How much is 2 much or not enuf.
cool_hardware52
Contributor
Any BC need to be able to two things;
1) Float your rig at it's heaviest (full tank) without you and your buoyant exposure in it.
2) Compensate for the loss of buoyancy of your exposure suit. Wetsuits compress and you need to be able to compensate for this to remain neutral.
Which ever is greater, i.e. #1 or #2 will determine the absolute minimum lift necessary.
I'll give you hint. In cold water it's almost always #2 that governs, and in tropical conditions it's usually #1.
Tobin
Most the guys I dive with use somewhere in the 55#-65# area depends on what your taking with you gear and exposure wise. Some use a minimalistic approach and rant on and on about how much drag you get with bigger ones and air consumption. But really its not a big deal...to me anyway
GrumpyOldGuy
Contributor
OK, I have a question for you. If you plan your personal air reserve to allow you AND your buddy to ascend safely, why don't you do the same for your BC? If my buddy is OOA, I want to be able control the bouyancy for both of us, which means I want 2X more lift than I need normally.
*Floater*
Contributor
If you search in the BCD section titles with "lift" in them then you'll get a good answer.
Basically it should be enough to offset the gas in your tank/s when full and the compression of your wetsuit.
For a large tank that's about 10# of air, for an AL80 it's 6#.
Next see how much lead it takes to sink your wetsuit. If it's takes more than 20# then you might want to consider a wing with more than 30# of lift, but actually even then you don't need to (for single tanks) because your wing only needs to offset about half the compression of your wetsuit if you are otherwise weighted correctly.
First, about 25% of the buoyancy loss of your wetsuit happens during the first 10' feet, and it's only at 10' during that last safety/deco stop or below that you need to remain neutral. Second, another 25% of your wetsuit's buoyancy is not lost (exponential curve thing), at least not in recreational depths, so you could just use 50% of your wetsuit's total buoyancy as the amount your wing needs to compensate.
So if your wetsuit takes more than 40# to sink but you are otherwise squared away then you might need a wing with more than 30# lift, but actually you still have some to spare, namely your lungs can generate some additional lift.
I can personally blow up a 25# SMB in 3 full breathes , so I figure my lungs can generate about 8# of buoyancy when full vs. empty. Most people should be able to put out at least 5#.
Of course you want to have some sparse capacity just in case and people are probably better served following Tobin's rules of thumb, but my point is that no single tank diver should really "need" more than 30# of lift, though I'm sure some diver's prefer more for various reasons.
By the way, the wetsuit figures are based on this person's article, or more precisely I assume his wetsuit compression test is accurate and representative of typical wetsuits, so that's where I get my 25% estimates: DIR-diver.com - How much lead?
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