30# wing or 40# wing - still not clear...

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Turtle Time

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I've read up on boyancy and am still unclear if I'm missing something. It seems that a 30# wing is fine for single tank dives. Is the only way to figure it out to get into 10 feet of water and neutralize w/ empty bladder and add 9lbs suit compression and 6lbs air loss...as they say on the halcyon site. Is the kicker If you use steel vs Alum tanks?

TT
 
Dig around, there are plenty of threads that cover this one.

As for myself, I just recently bought a Deep Sea Supply LCD30 with a stainless backplate.
I dive a 3mm wetsuit, sometimes a 1mm wetsuit.
I don't need any weight with this rig.

That being said, 30lbs. of lift is more than I need. Luckily, the DSS LCD30 is a pretty streamlined wing. In reality, a 20lb. wing would have been enough lift for me. The LCD30 is a little longer than the 20, and I felt that it would trim out better for me.

I could have went with their Torus 26, but I wanted their horseshoe shaped wing so that I could have access for minor bladder repairs. I'm in Guam and will be taking trips to Yap, Palau, and Chuuk.
In the event that I were on a trip and had a puncture, I wanted to be able to fix something myself.
That's why I chose a 30lb., a 20lb. would do.
I'm guessing that there aren't too many situations where you would need 40lbs. for a single wing.
Ask Tobin, in the "Deep Sea Supply" section of the board.

-Mitch
 
Your wing needs to be able to do two things . . . Float your rig at the surface, and compensate for lost buoyancy at depth.

For the first, you have to figure out the negative buoyancy of all your gear. With the exception of the highly negative Faber tanks, you're unlikely to have a tank that's more than 11 pounds negative when full. Your backplate is five or six pounds negative. You might have weight plates or a weighted STA adding another 8 lbs or so. Add a reg, D-rings, can light, and with a full 130, you might be right at the capacity of a 30 lb wing to keep the rig afloat. But if you are using more typical tanks (Al80, LP95, HP100s) you should still be fine, even with the weighted rig.

For the second, you need to figure the maximum buoyancy you can lose at depth. It varies from wetsuit to wetsuit, and with age, and no figures are published on it, but I know that the GUE guys checked it with a 7 mil wetsuit and came to the conclusion that you could lose about 20 lbs of lift at 100 fsw. If you were wearing layered 7 mil, as some folks do here in the sound, I suppose you might be able to lose even more, which might push the capacity of a 30 lb wing. Diving dry and assuming a complete suit flood is another circumstance where you'd lose a fair amount of lift, although it takes time for water to displace all the gas in one's insulation.

So I guess the answer is that there might be some circumstances right on the margin, where you would be pushing the capacity of a 30 lb wing, but for most configurations, even in cold water, 30 lbs is likely to be enough.
 
I've read up on boyancy and am still unclear if I'm missing something. It seems that a 30# wing is fine for single tank dives. Is the only way to figure it out to get into 10 feet of water and neutralize w/ empty bladder and add 9lbs suit compression and 6lbs air loss...as they say on the halcyon site. Is the kicker If you use steel vs Alum tanks?

TT

The only way to "be sure" (aka "field testing") is to dive to 100 ft, and see if your 30 lb B/C gets you off the bottom at that depth with all your normal gear. And then when you are back on the surface, inflate the B/C completely and see if your head is out of the water enough so that you can breathe without your regulator in your mouth. Then take off your gear in the water, and see if it floats when completely inflated on its own, without you holding it up. Those are the 3 major considerations for deciding on the amount of buoyancy that you need and want.

With a single tank, there will be a difference in performance of your B/C between the beginning of the dive and the end. At the end, you will "weigh" 6 lbs less, because the air in a single tank weighs about 6 lbs (0.08 lbs/cu ft x 80 cu ft).

At 100 ft, there will be a difference in performance of your B/C because your wetsuit has compressed, if you are diving with a wetsuit. Since the wetsuit will be less buoyant at depth, the B/C needs to carry the weight of the gear more on its own, rather than shallow, when the suit also does some of the lifting as well. With a drysuit this is not an issue.

When the gear is floating on its own, there will be a different result depending on whether you wear all your ballast on your weight belt, as opposed to splitting the weighting between a backplate and your belt. Some backplates also have extra weight due to weight plates and/or an STA.

Have fun trying this all out. The game of scuba toys is all about playing around with different combinations and making discoveries. Since everyone configures differently, there is no one quick easy answer to your excellent question.
 
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...Dig around, there are plenty of threads that cover this one.

As for myself, I just recently bought a Deep Sea Supply LCD30 with a stainless backplate.
I dive a 3mm wetsuit, sometimes a 1mm wetsuit.
I don't need any weight with this rig.

That being said, 30lbs. of lift is more than I need. Luckily, the DSS LCD30 is a pretty streamlined wing. In reality, a 20lb. wing would have been enough lift for me. The LCD30 is a little longer than the 20, and I felt that it would trim out better for me.

I could have went with their Torus 26, but I wanted their horseshoe shaped wing so that I could have access for minor bladder repairs. I'm in Guam and will be taking trips to Yap, Palau, and Chuuk.
In the event that I were on a trip and had a puncture, I wanted to be able to fix something myself.
That's why I chose a 30lb., a 20lb. would do.
I'm guessing that there aren't too many situations where you would need 40lbs. for a single wing.
Ask Tobin, in the "Deep Sea Supply" section of the board.

-Mitch


Oxycheq sells a great 18 lb wing which works perfectly together with a 1/2 mm suit or 3 mm suit. I would guess DSS offers something similar.
 
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So I guess the answer is that there might be some circumstances right on the margin, where you would be pushing the capacity of a 30 lb wing, but for most configurations, even in cold water, 30 lbs is likely to be enough.

A lot may depend on where you carry your weight. Integrated weights may not work if you are going to push your wing capacity.

A friend of mine has a 7mm FJ (XL) that is about 32 lb buoyant. (It took 32 lb of lead attached to the suit to sink it in a swimming pool.) So between that and his inherent buoyancy in SW, he requires a little over 32 lb of neg buoyancy to descend and maybe a bit more than that to hold stops. You can probably pick up at least 30 and 50% of the weight you need with your choice of tank and BP. But the rest would have to be on your person rather than your gear to allow your gear to float at the surface. Pushing the limit is probably a bad idea. First there is the question of the manufacturer's buoyancy rating of your wing vs what you actually achieve in your configuration. And then that are those $10 OPV with the $2 spring that might let out a burp when the rig hits the water.
 
I've read up on boyancy and am still unclear if I'm missing something. It seems that a 30# wing is fine for single tank dives. Is the only way to figure it out to get into 10 feet of water and neutralize w/ empty bladder and add 9lbs suit compression and 6lbs air loss...as they say on the halcyon site. Is the kicker If you use steel vs Alum tanks?

TT

Wing capacity is mostly a function of the buoyancy of your exposure suit. You have provided no information about your configuration.

The reason why divers need Buoyancy Compensators is their exposure suits loose buoyancy as they descend.

If you jump in the water in your swim trunks there's no neoprene to compress. If you jump in the water in a full 7mm suit with hooded vest there may be 25+ lbs worth of buoyancy to be lost as the diver goes deeper.


The ultimate goal is to be weighted so your total ballast is equal the buoyancy of your exposure suit at your shallow stop depth with a (near) empty tank.

If your back plate + harness + regulator + empty tank is less than this minimum required ballast add a weight belt.

If your back plate + harness + regulator + empty tank is more than this minimum you need to change to a less negative tank, or less negative back plate.

**The solution to being over weighted is not a larger wing**

You have provided no suit info or tank info so the best I can do is provide an example.

If you are diving locally I'll assume cold water (7mm wetsuit) and steel tanks.
Any "personal buoyancy" will impact your total weighting, but will not require compensation, fat doesn't compress at depth.

A medium SS plate and harness is about -6 lbs, a reg is -2 and a full HP 100 is about -10. That makes your "rig" about -18 lbs with a full tank, and about -10 with an empty tank.

If your 7mm suit is + 26 lbs you will need about 26 -10 (ballast of rig) = 16 lbs additional ballast. I'll assume you choose to add 8 lbs of this 16 to your rig via bolt on weights or pouches etc.

Now your rig is 18 + 8 = 26 lbs negative with a full tank, and provides about 18 lbs of ballast with an empty tank. 26 -18 = 8 lbs in a belt.

To float this rig, even with a steel tank and extra bolt on ballast you need a wing that is greater than 26 lbs.

Your wetsuit cannot loose more buoyancy than it starts with and I've **Assumed** it was +26. You need a greater than 26 to be able to compensate for a fully compressed wetsuit.

30 > 26. A 30 lbs wing would be fine. It is a rare wetsuit that is more than 30 lbs positive, and it is a rare single tank rig that will be more than 30 lbs negative.

Tobin
 
If you did not need weights...then how do deal with the situation which would call for ditching weight?

TT
 
If you did not need weights...then how do deal with the situation which would call for ditching weight?

TT

Is this question directed to me?

My recommendation for cold water diving in a wetsuit (read lots of total ballast) is to have at a minimum 4 lbs of ditchable ballast. That's enough to establish positive buoyancy at the surface in the event of a BC failure.

It's worthwhile to keep in mind that this works only if the diver is properly weighted to start with. If they are 12 lbs over weighted ditching 4 doesn't help much.

In cold water / heavy wetsuits and single cylinders I want to start the dive neutral at the surface with no gas in my wing and a full tank.

I will rely on the compression of the suit from the surface to my shallow stop depth to offset the weight of the gas I will consume during the dive.

If I'm neutral at the surface with no gas in my wing and a full tank I will never be any heavier, I have 100% of my wings capacity available for "comfort" at the surface, and dropping 4-6 lbs will certainly make me positive.

Tobin
 
First, Thank you all so much!!

Do you always make some weight ditchable? By say taking off the weighted STS and adding two 4 pound ditchables? Or pretty much always you'll need more than 8lbs of added weight?

I know not enough info...
For this example say a 3mm shorty, al80 tank, no stuff, and a not buff 190lb diver?

TT
 
https://www.shearwater.com/products/teric/

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