Very interested in BP/w. Confused/help

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Hi Tom, welcome to ScubaBoard.

Regarding wing size, rjack321 and Dubious have already taken a crack at explaining this. Sometimes hearing the same thing in different words can be helpful, so I'll throw in my 2 cents in the bucket.

Your wing needs to be large enough to achieve two things, and two things only. (1) To compensate for the maximum difference in your buoyancy throughout the dive, (2) Be able to float on the surface in case you want to remove it in the water, or maybe toss it into the water and jump in after it.

(2) is easy -- like rjack says, you need a wing whose lift exceeds everything negative on your rig. That would be the backplate, tank, any attached lead, and conceivably gear (like if you have a super heavy can light). A typical steel backplate is -5 lbs or so, full typical steel tank -10 lbs or so. I also like to put 4 lbs of lead in trim pockets. So for (2), I need about a 20-lb wing. If you hate heavy weight belts / harnesses and want to stick it all on the rig, OK, fine. A 30-lb wing supports roughly 15 pounds of lead, a 40-lb could do around 25 lbs of lead, and so on.

(1) is the one that people often are confused by. It has absolutely zero to do with your body's density, the amount of lead you're carrying, the material of your tank, the material of your backplate, or anything else. The big ones that do matter are the volume of gas in the tank, and the volume of the gas in the materials of your suit.

For tanks: At the beginning of your dive, your tank is full, so an HP100 contains 100 cubic feet of air, which weighs about 8 pounds. . Suppose you were to completely empty the tank during your dive (not a great idea of course, but suppose). At the end of the dive, the tank will therefore be 8 pounds lighter, so your wing needs at least 8 pounds of lift to compensate for this difference.
Further reading on tanks: Here is a chart of the weight of air, here is a chart the buoyancy of many common tanks.

For exposure suit: At the surface, my thick wetsuit needs roughly 16 lbs of lead to sink it, so we can say that it is 16 lbs positive. As I descend, the gas trapped in the materials of the suit compresses from the pressure. If I were to go super super deep, that buoyancy would go close to zero. So my wing would need an additional 16 lbs of lift to compensate for exposure gear. In the worst-case scenario in my wetsuit, I therefore need a minimum of 24 lbs of lift. In fact, my I have a 32-lb wing, which works just fine. I also dove it in warm water earlier this year, and it worked great.

The material in my trilam drysuit is pretty much neutral, so I could probably get by with a smaller wing. Since you have a neoprene drysuit, the materials will be somewhat positive, but certainly less than a thick wetsuit. So again, the 30-lb wing range is probably just fine, and is a good rule of thumb for all single-tank diving. In warm water where you typically have smaller tanks and tiny or no exposure gear, 15-20 lbs is common. 40-pound wings and larger would make sense if you either had a super duper thick wetsuit (like 2 layers of 7mm, thick gloves/boots/hood), or if you had multiple tanks (adding another HP100 would add another 8 lbs of gas to compensate for), or as mentioned above, if you just want to put a s***load of lead on the rig.

All of the above only works if you are "properly weighted." Which of course, different folks have different views on. What I mean by it is, you are neutrally buoyant near the surface with an empty tank. Because that is the most buoyant you'll ever be, if you are neutral there, then you know that no matter your depth or amount of gas remaining in the tank, you will be able to achieve neutral buoyancy. If you are positive near the surface with an empty tank and empty wing, then you need more lead. If you are negative near the surface with an empty tank, then it is safe to remove some lead. 40 pounds is a LOT of lead, I suggest that you do a weight check at the end of a dive (so that your tank will be near-empty). Just completely dump your BC/wing, and see if you are able to hold a shallow stop. If you sink, give some lead to your buddy or set it on the ground. Keep removing lead until you're neutral. Now you have the perfect amount of weight. As one point of reference, I'm 5'11, 165lbs, dive in 50 degree water, and have been using about 20 lbs of lead in my drysuit / SS backplate / steel single tank. I intend to try a little bit less lead next dive, and expect I'll end up with no more than 16 lbs when I have it dialed in.

Best of luck, hope this helps!
 
Thank you all. I have learned a lot, and have much to think on. I can see i was looking at the need for lift incorrectly. I am now trying to figure out how much lead I would need for the coldest diving I might do, if I were to get a SS backplate. Layering wool and fleece seemed to add a lot of buoyancy, coupled with the neoprene drysuit, hood, gloves, and the back inflate bcd ( which is positively buoyant, but I don't know how much).

Then I can figure how much weight I might have on the BP/W. I would rather have a little extra lift, than barely enough.
 
If you dive with me you need a wing big enough to float your tanks and any integrated lead because on my RIB you have to ditch your gear in the water before you can climb back aboard. Its easy to take off a weightbelt and throw it over the tube. Then ditch the BP/W and tank. Then swim in and haul the tank in behind you.
@Tom Schirm,

Having enough lift for ditching/donning at the surface is not something everyone considers. I had 2 wings in the past for my twinsets, a 40 lb one for shore diving, and a 50 lb one for boat diving. While I have not experimented with that, I have been told by others that even fully inflated, my doubled HP100s will sink to the bottom if they are not on my back.
 
An HP100 is 10 lbs negative when full. So less than 30 lbs negative total with a SS plate and all the trimmings. Do you have a bunch of lead attached to the plate/harness?
 
I'd go with a stainless steel backplate. It will help with decreasing weight with cold water diving and in the caribbean if stuck with an al80. I'd go with a 30lbs wing. I'm a very very big fan of halcyon bp/w. About 50 people will chime in and say it's overpriced and not worth it. For me, the quality is one of the best but the customer service is as well. It's not unheard of for halcyon to repair a 15 year old wing under warranty. If you're going for cheaper options dive gear express has decent options. Avoid the "comfort" harnesses with the buckles and padding. It's toitally unnecessary. For OW diving I like the halcyon cinch system so I can easily go between a drysuit to a bathing suit depending on where I dive. It is completely unnecessary, but is nice to have occasionally.


I have heard Halcyon is great, but it is out of my budget.

An HP100 is 10 lbs negative when full. So less than 30 lbs negative total with a SS plate and all the trimmings. Do you have a bunch of lead attached to the plate/harness?

I have never used a BP/W yet. My thought was some weight in a harness, and some on the BP/W. I am not sure how much less lead I will need going to a BP/w. I realize a SS backplate is - 5 to -6 lbs, but I am not sure how positively buoyant my current Back inflate Dimension i3 is which obviously then requires lead to counteract. I also was probably overdressed in undergarments during the winter ocean dive with 40 #'s of lead needed.
 
An HP100 is 10 lbs negative when full. So less than 30 lbs negative total with a SS plate and all the trimmings. Do you have a bunch of lead attached to the plate/harness?
Around here in salt water probably 75% of people in DOUBLE 100s use a SS plate, a 10lb V weight, and a small amount of lead on a belt. Which will float enough to ditch in the water after dive 1 with a 40lb doubles wing. It's not common but occasionally someone needs to ditch a full set of doubles and climb back in the boat - leaking glove or neck seal are the most common reasons.

A 30lb wing is fine to float a single 100. Most Puget sound singles wings for any steel tank with SS plate are 30-40lb lift. 40 being a MAX. I think the smallest single wing for steel tanks and drysuits that is reasonable here is in the 24lb range. You could probably squeak by with an 18 or 20lb for shore diving but it would feel inadequate to keep your head up with a full tank off a boat.
 
A 30lb wing is fine to float a single 100. Most Puget sound singles wings for any steel tank with SS plate are 30-40lb lift. 40 being a MAX. I think the smallest single wing for steel tanks and drysuits that is reasonable here is in the 24lb range. You could probably squeak by with an 18 or 20lb for shore diving but it would feel inadequate to keep your head up with a full tank off a boat.
Agreed. My VDH 18# wing floated my steel plate and an HP120 with no problem in Coz last fall. But that used up all but 3 or 4 pounds of its rated lift. It wouldn't be enough to get you positive at the bottom if you were wearing anything thicker than a 5mm (assuming optimal weighting). A 24 would be technically enough to float a full tank and flooded drysuit, but you'd have to have the weighting spot on. The 30 isn't much larger and gives you wiggle room if you are slightly overweighted.
 
I have never used a BP/W yet. My thought was some weight in a harness, and some on the BP/W. I am not sure how much less lead I will need going to a BP/w. I realize a SS backplate is - 5 to -6 lbs, but I am not sure how positively buoyant my current Back inflate Dimension i3 is which obviously then requires lead to counteract. I also was probably overdressed in undergarments during the winter ocean dive with 40 #'s of lead needed.
I found an old test that indicates the i3 is 1.5 lbs positive. BP harnesses are also slightly negative, so take the plate weight and add 2 pounds. Subtract that from however much you need with your i3.

FWIW, this matches my experience. I can drop 7 pounds when going from a rental jacket BC to my BP/W and your i3 is a pound or two less buoyant than a basic jacket.
 
So a 30# wing would work with either an 80 or 100 HP steel tank, ss backplate as long as I don't put to much lead on the bp/w. MOre weight would need ot be on a blet or harness?
 
So a 30# wing would work with either an 80 or 100 HP steel tank, ss backplate as long as I don't put to much lead on the bp/w. MOre weight would need ot be on a blet or harness?
Sounds right. With a 30 lb wing you should be able to put 15-ish pounds of lead on the rig with a steel tank, and another 5 or so with an aluminum tank. Any other lead will need to go somewhere on your person.
 
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