BC Lift Question

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MRTdiver

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I enjoy a lot of what is on this post and lean towards a smaller wing. I was in that line of thinking but the lds and one of the wing manufacures are steering me to a larger wing (60#). I am contemplating double 130 on a ss plate. 22 neg on tanks full, 8 lbs gear, 6 lbs plate only gets me 36 negative. Adding 26 lbs posative from the drysuit implies i am 10 neg and only need 10 lbs of extra lift to start. By the end of the dive i would shed 20lbs of air so i would need an extra 10 to start. That would still only imply I need 20 lbs of lift.

Do you agree with this math? Also if the suit fails I loose the 26 lift at the beginning or end of the dive when tanks are 22neg and 2 neg, respectively I would 36 neg and 16 neg, respectively. Seems like a smaller wing could swing that espc as one could ditch the 10 lbs of lead. what am I missing

I have doubled 130s. Here's my numbers (negative weight):

Double Tanks 130 ft[SUP]3[/SUP] tanks in salt : ~ -23.4 Ibs neg buoyancy (full) (- 11.7 lbs each see XS Scuba specs)
+ must factor in tank bands & manifold (4 Ibs?)
Dual regs (3-4)
SS Backplate (6),
Canister light & backups (2)
Reels & spools (3) (Cf. Tobin's numbers)
= ~42 Ibs lift needed. I'm purposely leaving out the positive buoyancy of a drysuit or wetsuit. So about a 40# wing is the bear minimum.

And seeing if this measures up to real life... I'll quote lamont discussing wings (Post):
Actually, I've been using the 40# evolve with the double-130s lately since its just been with nitrox with no stages or anything else.
This is about as low as a person normally would have for a wing. Though commonly we will use ~55# for doubled tanks with the weight of the Worthington HP 130s/LP 108s, because commonly stages are added into the equation later on.
 
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gcarter

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I have doubled 130s. Here's my numbers (negative weight):

Double Tanks 130 ft[SUP]3[/SUP] tanks in salt : ~ -23.4 Ibs neg buoyancy (full) (- 11.7 lbs each see XS Scuba specs)
+ must factor in tank bands & manifold (4 Ibs?)
Dual regs (3-4)
SS Backplate (6),
Canister light & backups (2)
Reels & spools (3) (Cf. Tobin's numbers)
= ~42 Ibs lift needed. I'm purposely leaving out the positive buoyancy of a drysuit or wetsuit. So about a 40# wing is the bear minimum.

And seeing if this measures up to real life... I'll quote lamont discussing wings (Post): This is about as low as a person normally would have for a wing. Though commonly we will use ~55# for doubled tanks with the weight of the Worthington HP 130s/LP 108s, because commonly stages are added into the equation later on.

(I am checking my learning here)

So is it fair to say that when choosing lift for a wing, the assumption is that it should be sized without exposure protection in the equation?

I am basing this on the idea that you will weight to compensate for wetsuit or drysuit (air only for anti-squeeze) buoyancy and that takes it out of the equation.
 

MRTdiver

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So is it fair to say that when choosing lift for a wing, the assumption is that it should be sized without exposure protection in the equation?
Essentially divers wear wings with sufficient lift to enable them to maintain neutral buoyancy and go slightly positive at the depths to which they dive. The ability to maintain neutral buoyancy at any stage during a dive becomes more important during a deeper dive.

In sizing for a wing perhaps I am wrong in leaving out the positive buoyancy provided by our exposure protection (wetsuit/drysuit) in my calculations above (post 51). But this was some of my reasoning…

Now I always wear a drysuit with the heavy doubled 130s for redundant buoyancy. But a drysuit can sustain a large tear in the wrists etc. rendering it's buoyancy virtually to nil.

And wearing a full 7 mm wetsuit with hood while providing ~+22 Ibs of lift at the surface, at 130 feet, the wetsuit will only provide ~+4.5 Ibs of lift. Being 4 atmospheres down that‘s 1/5[SUP]th[/SUP] of the buoyancy we had at the surface. I also keep in mind that wetsuits lose buoyancy as they age.

Imagine only wearing a 3mm. Its buoyancy would be very little at depth.

So the wing still needs to provide the needed lift at depth with a compressed wetsuit or deal with a catastrophic drysuit failure.
 

Sigma13

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Thanks for the input. I think I'll opt fit a 57# but feel better about my math and choice. Aside from that how do you like the double 130s. I've found them to be manageable in flat conditions but have not taken them to sea as I'm not sure how they fare with 6th waves. Rolling conditions and 125 lbs of gear and water weight on a ladder have kept me from trying.
 

MRTdiver

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Thanks for the input. I think I'll opt fit a 57# but feel better about my math and choice. Aside from that how do you like the double 130s. I've found them to be manageable in flat conditions but have not taken them to sea as I'm not sure how they fare with 6th waves. Rolling conditions and 125 lbs of gear and water weight on a ladder have kept me from trying.

With those doubled 130's I wear an AL backplate & drysuit for redudancy. The usual tendency among the diving community to use a higher poundage wing than one needs. This is almost always the case. In the ocean I was fine whether or not there are waves. Used to use a Hollis 60 Ib wing, that's really not needed. So now I dropped down in poundage and bought a couple Halcyon 55 Ib wings and really love them.

With these tanks the main thing I advise ppl on is to be physically in shape. As you know they are heavy. If you have knee problems then NO. If you don't do regular physical training, then NO. Because a person can easy injury themself more.
 
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