Wing size/lift calculation questions.

[elmer fudd]

Here's a strange thought I've had. I've considered for awhile now making a very small "wing", in the neighborhood of 6 lbs. Basically it would just be the minimum necessary in conjunction with ones lungs to maintain neutral buoyancy at most depths in a 7mm wetsuit.

What I'd like to try doing is using two pieces of surgical tubing running down either side of a backplate and then hooked to a power inflator. Inflated or deflated, it would be the most compact and streamlined wing possible. I did say this was a strange thought after all.

Of course, if I tried this and it did work, the next logical step would be a similar "BC" on my inner thigh, a la Spinal Tap.
This Is Spinal Tap - Cucumber Scene - YouTube

 

[elmer fudd]

Ah, not not really. If the corrugated hose separates from the bladder your kinda done using the BC for buoyancy.

Tobin

Yep, you're right. I misunderstood the earlier post. I was thinking she meant the LP hose, not the corrugated hose.

My bad.

 

[Peter_C]

Drysuit only divers that like to load up your rigs with all kinds of non ditchable weight, I have a question.
What if you were to have a catastrophic failure of your drysuit (total flood) and your inflator came undone so you have no redundant buoyancy whatsoever. Do you have enough of your weight on your belt to lighten up enough to swim you and your rig up?

If a double failure happened, as rare as it might be, I would first look to hand off my can light, then throw out some of my ditchable soft weight bags. At that point it shouldn't be too hard to swim to the surface. If still stuck to the bottom I could cut my weight belt in half, fill my smb, or completely drop the weight belt (Always a last ditch effort, unless at the surface). Much of that is going to depend on how much buoyancy I have remaining. As long as a person has a few minutes of air and doesn't panic, it shouldn't be a big deal.

NixdaxTo your primary point, I wouldn’t be very concerned about slowly sinking when full either. Most rescues are when cylinders are low. Same with removing tanks when boarding an inflatable. Sinking bottles can be an inconvenience at times, but far from a crime against humanity.

I dealt with a kit that sank for over a year. Shore diving I never even noticed it.

 

[Eric Sedletzky]

If a double failure happened, as rare as it might be, I would first look to hand off my can light, then throw out some of my ditchable soft weight bags. At that point it shouldn't be too hard to swim to the surface. If still stuck to the bottom I could cut my weight belt in half, fill my smb, or completely drop the weight belt (Always a last ditch effort, unless at the surface). Much of that is going to depend on how much buoyancy I have remaining. As long as a person has a few minutes of air and doesn't panic, it shouldn't be a big deal.


I dealt with a kit that sank for over a year. Shore diving I never even noticed it.

Good response, at least you're thinking about it, many people would not.

If it came down to it and you had to ditch a belt completely because your suit was flooded and your wing was junk you would not rocket to the surface because there would be no air cavity to speak of that would be able to expand enough to cause a rapid ascent. Some trapped air up high in the suit maybe or a high spot in a cut wing. But at that point I think just getting to the surface would be my primary goal. Where we dive a complete drysuit flood in 48 degree water means you would have only a few minutes to get something done or else paralasis and hypothermia will get you in short order.
That's why I think it's not the best idea to load up a rig with as much weight as possible just because somebody doesn't want to deal with a weightbelt or other form of ditchabloe weight.

 

[Eric Sedletzky]

Simple physics and common sense.

For cold water diving, if one does not hang 100% of their ballast on their rig, the buoyancy of the exposure suit will virtually always dictate the minimum required wing capacity.

OK, agree on the minimum rated buoyancy of the wing to cover the added weight at depth from suit compression.
But if a diver is weighted properly what difference does it make where they place their balast weights as long as they're not overweighted.
Unless of course you're refering to not having 100% of balast on the rig because it won't float on it's own, then I guess it would require a monster wing eh?

For cold water diving with "normal" sized single tanks I like to see ballast roughly equal to the weight of the gas carried on the divers person, i.e. weight belt or weight harness. For most that means ~8 lbs in a belt.

Tobin

OK, I dive in water that never leaves the high 40 for at least half the year, I think that qualifies as cold water.
I use a two piece wetsuit that requires me to wear a 20 lb weightbelt along with a steel 72 and a 4 pound plate. No other balast weights except for other stainless components such as cam buckles, waist buckle, and a handfull of keepers and D rings. If a 72 is not considered normal anymore then swap that out with an HP 100. BTW I have to drop 3-4 pounds when I switch.
I don't use a can light or carry much else that is negative. With this configuration I have to actually swim down before I achieve neutral buoyancy at about 10 feet. At the end of the dive I can hold a stop at 15 feet with an empty BC and control my stop with breathing alone. I figure I have my weighting about as good as it gets.

So, with your formula of a weightbelt equaling the weight of the air in a tank I should only have about a 5 pound weightbelt using a 72 and maybe a 7 with a 100.
So, if you don't mind please set me up how you think I should have my weights, wing size, balast attachment points, etc. We'll use your stuff since you are familiar with it.
Pretend I just walked into your shop and I asked you to set me up.
Go ahead.

 

[cool_hardware52]

OK, agree on the minimum rated buoyancy of the wing to cover the added weight at depth from suit compression.
But if a diver is weighted properly what difference does it make where they place their balast weights as long as they're not overweighted.
Unless of course you're refering to not having 100% of balast on the rig because it won't float on it's own, then I guess it would require a monster wing eh?


OK, I dive in water that never leaves the high 40 for at least half the year, I think that qualifies as cold water.
I use a two piece wetsuit that requires me to wear a 20 lb weightbelt along with a steel 72 and a 4 pound plate. No other balast weights except for other stainless components such as cam buckles, waist buckle, and a handfull of keepers and D rings. If a 72 is not considered normal anymore then swap that out with an HP 100. BTW I have to drop 3-4 pounds when I switch.
I don't use a can light or carry much else that is negative. With this configuration I have to actually swim down before I achieve neutral buoyancy at about 10 feet. At the end of the dive I can hold a stop at 15 feet with an empty BC and control my stop with breathing alone. I figure I have my weighting about as good as it gets.

So, with your formula of a weightbelt equaling the weight of the air in a tank I should only have about a 5 pound weightbelt using a 72 and maybe a 7 with a 100.
So, if you don't mind please set me up how you think I should have my weights, wing size, balast attachment points, etc. We'll use your stuff since you are familiar with it.
Pretend I just walked into your shop and I asked you to set me up.
Go ahead.

If a diver's rig represents 100% of their ballast, it must be roughly equal to the buoyancy of their exposure suit when the cylinder is empty.

In your example the rig would need to be about -20lbs. with an empty tank.

Add back in the weight of the gas (100 cuft tank) 8 lbs and the rig will be ~-28lb. with a full tank.

To float this rig with a full tank you need a wing larger than 20 lbs.


To compensate for the total compression of the divers suit you need a 20 lbs.

OTOH, if the diver was wearing a 8 lbs weight belt then the rig is only -20 lbs with a full cylinder.

The very same wing capacity is required to both compensate for the maximum possible change in buoyancy of the divers suit (20 lbs) and to be able to float the rig with a full tank, again 20 lbs.

This is *exactly* why I don't like to see 100% of a divers ballast on their rig for cold water single tank diving.

If one spends a little time considering the impacts of *where* the necessary ballast is carried there is absolutely no need to have an oversized wing just to float the rig.


Warm water is a different problem. Here suit buoyancy is often very little, 3-4 lbs for a 3mm suit is typical, but a BP&W + a full al 80 will be about -10 lbs.

Clearly 10 lbs > 3-4 so it's the requirement to float the rig that determines minimum wing size for thin suits and singles.

Tobin

 

[Akimbo]

If a diver's rig represents 100% of their ballast, it must be roughly equal to the buoyancy of their exposure suit when the cylinder is empty…

In the case of a drysuit, that might be a reasonable safety margin in the event of a catastrophic leak and the inability to dump weight in an emergency. However it is way above minimum in a wetsuit, especially a high density model like ZKY’s. You have to go far beyond most technical diving ranges to compress closed cell foam Neoprene to reach neutral buoyancy in sea water.

For a wetsuit, the loss of suit displacement due to compression at maximum operating depth plus compressed gas weight is more accurate — unless you accept the assumption that a rig must float rather than being a convenience in limited circumstances.

At least we aren’t discussing the need to lift the entire human head clear of the water in addition as I have heard specified in some dive shops selling jacket BCs… another 17 Lbs average.

 

[cool_hardware52]

In the case of a drysuit, that might be a reasonable safety margin in the event of a catastrophic leak and the inability to dump weight in an emergency. However it is way above minimum in a wetsuit, especially a high density model like ZKY’s. You have to go far beyond most technical diving ranges to compress closed cell foam Neoprene to reach neutral buoyancy in sea water.

One must go pretty deep to full crush any wetsuit, ~165 FSW, but the effects are distinctly non linear. In other words one does not loose 1/2 the suit buoyancy at ~82 FSW. The large % changes are in the shallow depths.

I'd caution that promoting weighting or BC requirements based on using wetsuits made from uncommonly encountered high density materials is *not* a service to the SB readership. Far too many *extra super duper mega stretch* suit are sold today, and these are pretty ease to compress.

In addition my methods do build in a certain margin for error in favor of too much capacity.

That's useful when divers are chronically over weighted.

Tobin

 

[Eric Sedletzky]

If a diver's rig represents 100% of their ballast, it must be roughly equal to the buoyancy of their exposure suit when the cylinder is empty.

In your example the rig would need to be about -20lbs. with an empty tank.

Actually 24 Lbs. with empty tank, remember there's a 4# plate in there.

Add back in the weight of the gas (100 cuft tank) 8 lbs and the rig will be ~-28lb. with a full tank.

To float this rig with a full tank you need a wing larger than 20 lbs.


To compensate for the total compression of the divers suit you need a 20 lbs.

OTOH, if the diver was wearing a 8 lbs weight belt then the rig is only -20 lbs with a full cylinder.

The very same wing capacity is required to both compensate for the maximum possible change in buoyancy of the divers suit (20 lbs) and to be able to float the rig with a full tank, again 20 lbs.

This is *exactly* why I don't like to see 100% of a divers ballast on their rig for cold water single tank diving.

If one spends a little time considering the impacts of *where* the necessary ballast is carried there is absolutely no need to have an oversized wing just to float the rig.


Warm water is a different problem. Here suit buoyancy is often very little, 3-4 lbs for a 3mm suit is typical, but a BP&W + a full al 80 will be about -10 lbs.

Clearly 10 lbs > 3-4 so it's the requirement to float the rig that determines minimum wing size for thin suits and singles.

Tobin

An 8 Lb weight belt, yeah OK, but then I would just have to find a place to put the other 12 lbs somewhere on the rig. To be honest I don't enjoy dragging a big wing around just for the convenience of having to float a rig that heavy on the surface. Most of the time I use only a small amount of air in it and it becomes annoying when I can feel that little bubble wandering around from side to side. I got stuck with a 40# wing (long story) and unless I'm using my 1/2" suit with a 120, that amount of lift is kind of useless.
I don't want to have to heaft that heavy of a rig up on me and it would make overhead donning not a possibility.

Someday I would also like to get into taking my rig off underwater and crawl back into holes for bugs with a hookah like Mel.
With an 8 lb weight belt It would be hard to stay down once separated from my rig. I know I said diver and rig as one unit but this is the exception.
For this reason I think I will stick to my 20 lb weightbelt and no added balast on my rig.

I agree 100% that all weight on the rig is a very bad idea. Try telling Aqualung, Scubapro, Seaquest and the others that weight integration with no where left to put weight on the diver separate from the rig is not the best idea and they will stare at you drooling out of the side of their mouthes with bubbles coming out of their nose.

What sparked all this is that I was out diving over the weekend with a new diver that was sold an Aqualung rig. During class they had the person way overweighted. We managed to decrease the weight by about 6 to 8 lbs.
There were pockets in the back by the tank that were full, and these plastic clip in weight holders on the sides that were loaded with weights.
Just switching to a steel tank and lightening the weight load by several pounds made a huge difference and increased the safety and joy for this person 10 fold.
Also during the last dive of the weekend the diver lost one of the weight pockets that had come unclipped and fell out. I went down and found it. trying to get it back into the holder was fun too, the plastic clip was not clipping in very well and I'm sure it will fall out again at some point. This BC only has a half dozen dives on it so far. It's just mind boggling to me the crap these LDS's push.
I was wearing nothing but a 72 steel tank on a strap harness (not even a plate) and a weightbelt over it. No wing, no added balast, no OCD over how much to put here or there, just cruising along snorkelling on the surface taking in the sights, beautiful..
We did quite a bit of surface swimming including crawling over kelp, navigating through feather boa, etc.


It just got me thinking of the complete polar opposite as to how the dive gear and mindset has changed from something that was once so simple to something so convoluted and complicated now.

 

[Akimbo]

… I'd caution that promoting weighting or BC requirements based on using wetsuits made from uncommonly encountered high density materials is *not* a service to the SB readership. Far too many *extra super duper mega stretch* suit are sold today, and these are pretty ease to compress…

The intent is promoting a thorough understanding rather than blindly accepting a questionable premise. The reality is the most highly compressible wetsuits inherently limit depth by nature of their insulation loss due to compression. If you need a 7mm at the surface, you will still have substantial buoyancy at 200'/60 Meters… if you can get that deep without suffering hypothermia. The type of material is irrelevant, only the loss of displacement at the intended maximum depth plus gas weight.

Having had catastrophic drysuit leaks with older wool underwear, I can attest that all displacement is not lost even at over 300'. It is more important that portions of lead can be jettisoned to prevent an uncontrollable ascent than a BC than can lift it all — especially given all the failure modes of a BC.

Needless to say, I believe the “BC as life support” argument is specious and does harm to the sport. Absolutely a convenience; but I’m not betting my life on a delicate plastic bag of air, a low tensile corrugated hose, a few tie wraps, and an inflator valve designed more for cost reduction than reliability.