Wings suitable for both double-7s and double-12s

[limeyx]

You have not provided any info as to what your suit buoyancy is, but I'll assume 22 lbs.

Double 130 will hold about 21 lbs of gas. Add 22 lbs of suit buoyancy and a few more lbs to allow for suit inflation at the shallow stop and you have 21 + 22 + 3 = 46 lbs. I'm not surprised that you found a 40 lbs wing insufficient.

Keep in mind that 46 lbs also represents the total ballast you need. You need 22 to simply offset the buoyancy of your suit, + 21 more to be negative by the weight of your gas + 3 more for extra inflation.

Your tanks are -1 each, empty. Plate and harness about -6, regs about -5, bands and manifold about -5, can light about -2 That totals -20 lbs. You need another 26 lbs of ballast. Lets say you choose to add 8 lbs of lead to your rig, and carry the rest of the 26 -8 = 18 in a belt. Your rig will now be -49 lbs with full tanks. That's another argument against using a 40 lbs wing.

It's easy to see that you need the 55 lbs wing for this rig, with or without the camera and or stages.

Tobin

Well, the actual numbers that I have are: 200G thinsulate/TLS350

6 pounds plate, 8 pound weightbelt and 21/35 in the doubles and Al80 stage.
Can light I dont think is -2 -- it's a helios 9, and I doubt it's even -1

I am guessing this case is more to do with the 8" tanks reducing the effective lift of the wing, and the wing simply holding me lower in the water than the slightly larger 55.

 

[cool_hardware52]

I am guessing this case is more to do with the 8" tanks reducing the effective lift of the wing, and the wing simply holding me lower in the water than the slightly larger 55.

By what mechanism will 8" tanks reduce the capacity of your wing. Doubles wing inflate outboard of the plate.

Tobin

 

[limeyx]

By what mechanism will 8" tanks reduce the capacity of your wing. Doubles wing inflate outboard of the plate.

Tobin

I am not 100% sure what is doing it. Until I do a test where *all* I do is change one thing at a time, I guess I wont know for sure.

I think even though it's a small difference, the 8" tanks might be a touch wider than the 7.25 -- maybe not enough to make a difference.

What I *do* know is:

Diving HP100's on a 40 pound wing with one AL40 is fine. I have not tried it with two, but would expect it to be OK too.

Diving 130's with a 40 pound wing and two Al40's is not so good.
I did dive the 130's with a single Al40 and 40 pound wing, but I dont remember how it was.

The weight of gas increase from 100's to 130's may be enough to just put me over the 40 pound edge, or it may be that the 130's are a bit longer and they affect the way I sit in the water.

Doesn't really matter that much in the end, as I know from experience which wings work in which circumstances -- the math is not as important as how it actually ends up working with my setup.

I am still confused on the loss of buoyancy with failed suit issue (and this is a genuine question, not a troll -- let's just say I didn't do so well in high-school physics

 

[cool_hardware52]

Interesting, I wasn't aware that a flooded d/suit would operate quite like that.
I am definitely not willing to try it in 54F water right now though

So to get this straight, you are saying that with a TLS350 drysuit (essentially incompressible -- and I guess doesn't have much inherent buoyancy), and say 200G thinsulate u/garments.

Assume that I measure them to be 20 pounds buoyant with me in it, and I dump all available gas.

Now, open the zipper completely. Now the buoyancy I have is what? 20 pounds less ?(minus my inherent personal buoyancy generated from eating too many pies at christmas)

Yup, that's about it. The shell suit is incompressible, but it's not inherently buoyant.

Your undies might be incompressible, but they can saturate. Thinsulate fibers are hydrophobic, thinsulate material can saturate.

Tobin

 

[BarryNL]

Barry,

There are very specific reasons why I suggested a 43 lbs wing as a minimum. I've detailed these for you twice already; You need to be able to offset both the potential loss of buoyancy from a total suit failure, and be able to stay at the surface when negative by the weight of your back gas + 2-3 lbs.

If you want to ignore these basic requirements and raise arguments based on wing sizes that are just simply unsafe and insufficient, (22 lbs doubles wing for example) then I have to ask why you posted your original question.

If you are already certain you have all the answers why bother asking? I wish both you and your fundies instructor the best of luck.

Tobin

Why is this such a big issue? All I'm saying is that you need more lift to counteract the negative buoyancy of doubles and stages than you need for doubles alone. If you read my post you'll notice the "22" figure is just for illustration - I'm not suggesting a wing this small (if such a thing exists).

Anyway, I e-mailed DIR Zone to ask their advice and they say their Stream 20 litre model is recommended for both double-7s and double-12s with stages. So, I have my answer.

 

[cool_hardware52]

I am still confused on the loss of buoyancy with failed suit issue (and this is a genuine question, not a troll -- let's just say I didn't do so well in high-school physics

Why does a foamed neoprene wet suit loose buoyancy when you descend? Because it becomes more dense, i.e. the weight per unit volume changes. The weight does not change, but the volume does, your suit gets smaller.

This is not what we are concerned with in a total failure of a Drysuit.

If you take your shell suit, just the shell and throw it in the pool you will eventually find it at the bottom, assuming the legs are filled. Why? Because Trilam is heavier than water.

Thinsulate is a polyester fiber. Polyester has a specific gravity around 1.5 If you stick your thinsulate garment in a 5 gallon bucket, it will saturate and sink.

How now do we get an undergarment that's made from a material that's heavier than water, and a shell suit that's made from a material that's heavier than water to become buoyant?

Same way we get steel ships to float, by displacement.

Let's we put you in your undies and drysuit and stick you in neck deep water and have you vent all the gas you can. This simulates what can be achieved at the surface at the beginning of a dive.

Now I'd ask you to descend to 100 fsw without adding any gas to your suit. Did the squeeze increase? I know it does in my suit. Are you more negative than you were at the surface? If your suit has no compressible gas in it how do you account for the squeeze?

It is this gas volume that accounts for the fact that your suit is positive at the surface even after you have vented all the gas you can, and it is this volume that can be lost in a total suit failure.

Tobin

 

[cool_hardware52]

Anyway, I e-mailed DIR Zone to ask their advice and they say their Stream 20 litre model is recommended for both double-7s and double-12s with stages. So, I have my answer.

20 liters is about 44 lbs of lift. We have a winner.

Tobin

 

[BarryNL]

Diving HP100's on a 40 pound wing with one AL40 is fine. I have not tried it with two, but would expect it to be OK too.

Diving 130's with a 40 pound wing and two Al40's is not so good.
I did dive the 130's with a single Al40 and 40 pound wing, but I dont remember how it was.

Now that is good to know. I should be fine then using a wing with 44 lbs lift with double-12s and Al40's.

I am still confused on the loss of buoyancy with failed suit issue (and this is a genuine question, not a troll -- let's just say I didn't do so well in high-school physics

Well, basically your drysuit keeps you warm by trapping a lot of air in the undersuit. If the suit fails all the air gets replaced by water and you lose the buoyancy of it. I think the figures given here suggest a drysuit/undersuit traps around 10 litres of air when inflated just enough to prevent squeeze; hence 10 kg (22 lbs) of buoyancy.

I'm afraid someone - probably JeffG - will be along to call you a troll in a minute though

 

[JeffG]

I'm afraid someone - probably JeffG - will be along to call you a troll in a minute though

No. Why would I?

 

[BarryNL]

Just him trolling I suspect.

Maybe he will be one of the first ones gone when they put the new DIR forum rules in.

No. Why would I?

Let's just call it 'modus operandi'.