Cold water Wing lift - again

[dumpsterDiver]

Considering that Dumpster diver IS a freediver.....the real thinking for him may need to be about..."why should a scuba diver be weighted DIFFERENTLY than a freediver?

As long as I have been diving, I am pretty sure I have always used freedive style weighting for my scuba diving....with the exception of a few 300 foot deep tech dives where we had to drop at about 300 feet per minute, to hit a wreck in a huge current...and even here, it was instantly ditchable weight--and had I ditched it, I could still easily hold the 20 foot stop without exertion.

Matching very thick buoyant wetsuits, to heavy tanks and very negative bp/wing set ups, looks too much like an invitation for Darwin to visit.

A Scuba diver should be weighted very differently than a freediver, especially if a thick suit is involved. Also, the weighting of a freediver is very dependent upon the planned depth of the dive, while a scuba diver may well choose his ballast to be able to attain neutral buoyancy at any depth (and with any amount of air in his tank).

This is not a trivial a distinction. Freedive weighting must be dialed in very precisely for safety and maximum performance while a well skilled scuba diver can easily dive with extra ballast with little difficulty (assuming they have sufficient lift in the BC to accommodate any extra ballast).

A freediver wearing a 5 or 7 mm suit and planning to dive below 40 feet is going to be significantly buoyant at the surface. He will need to kick down hard, maybe over come 10-12- 15 lbs of buoyancy at the start of his dive so that when he reaches a depth of around 30 feet or so, he will be neutral. As he descends further, he will become increasingly heavier. Wearing more ballast would aid his descent, but is very dangerous because it will cause him to be too heavy coming off the bottom. A properly weighted freediver will be pretty buoyant and can stop kicking and rest and glide to the surface from a depth of 15 or 20 feet.

The deeper a freediver is going to dive, the less lead he should wear.

Also, remember, freedivers are MUCH more affected by depth, because their lungs are compressing at depth - something that does not occur for a scuba diver. So the "swing" of a freediver's buoyancy is considerably greater than that of a scuba diver traversing the same depth range.

As has been discussed, a scuba diver does not want to be rocketing to the surface when they reach 15 or 20 feet.

So there there should be a significant difference in the weighting of a freediver versus a scuba diver in cold water with a suit.

If a freediver wants to be able to dive very shallow, and lay on the bottom and hunt fish in 8 or 12 ft depth, then he will need to be weighed to be negative at this depth and he will need a lot more lead and in this situation, his weighting would be very similar to that of a scuba diver.

The effects of the crushing of the chest on a freediver is pretty significant, even at 40 or 60 feet. In this video, I am wearing my freediving suit and freediving weightbelt and going down with a 13 cu-ft pony bottle. The pony bottle is close to neutral - maybe a lb negative with the regulator etc. So the only real difference is scuba versus freediver.

On a normal freedive, at 60 feet - even with a thin suit - I am pretty darn negative. I will be laying on the bottom to support myself and when I begin the ascent, I can feel being heavier than I like. The feeling is VERY different when using a neutral pony bottle which makes me a scuba diver and eliminates the chest crushing effect. In this video, you can see that when I start the ascent from 60 feet, I am actually neutral or maybe even floating up a little (positive buoyancy).

FYI. the solo dive is recorded from a gun mounted go pro which was left filming when the gun was wrapped up around a pole and "abandoned" during a freedive. The pony bottle was later used to make the recovery easier. A good freediver would have done it all on a breathhold.

[video=youtube;r-L9extLDZQ]http://www.youtube.com/watch?v=r-L9extLDZQ[/video]

 

[danvolker]

A Scuba diver should be weighted very differently than a freediver, especially if a thick suit is involved. Also, the weighting of a freediver is very dependent upon the planned depth of the dive, while a scuba diver may well choose his ballast to be able to attain neutral buoyancy at any depth (and with any amount of air in his tank).

This is not a trivial a distinction. Freedive weighting must be dialed in very precisely for safety and maximum performance while a well skilled scuba diver can easily dive with extra ballast with little difficulty (assuming they have sufficient lift in the BC to accommodate any extra ballast).

A freediver wearing a 5 or 7 mm suit and planning to dive below 40 feet is going to be significantly buoyant at the surface. He will need to kick down hard, maybe over come 10-12- 15 lbs of buoyancy at the start of his dive so that when he reaches a depth of around 30 feet or so, he will be neutral. As he descends further, he will become increasingly heavier. Wearing more ballast would aid his descent, but is very dangerous because it will cause him to be too heavy coming off the bottom. A properly weighted freediver will be pretty buoyant and can stop kicking and rest and glide to the surface from a depth of 15 or 20 feet.

The deeper a freediver is going to dive, the less lead he should wear.

Also, remember, freedivers are MUCH more affected by depth, because their lungs are compressing at depth - something that does not occur for a scuba diver. So the "swing" of a freediver's buoyancy is considerably greater than that of a scuba diver traversing the same depth range.

As has been discussed, a scuba diver does not want to be rocketing to the surface when they reach 15 or 20 feet.

So there there should be a significant difference in the weighting of a freediver versus a scuba diver in cold water with a suit.

If a freediver wants to be able to dive very shallow, and lay on the bottom and hunt fish in 8 or 12 ft depth, then he will need to be weighed to be negative at this depth and he will need a lot more lead and in this situation, his weighting would be very similar to that of a scuba diver.

The effects of the crushing of the chest on a freediver is pretty significant, even at 40 or 60 feet. In this video, I am wearing my freediving suit and freediving weightbelt and going down with a 13 cu-ft pony bottle. The pony bottle is close to neutral - maybe a lb negative with the regulator etc. So the only real difference is scuba versus freediver.

On a normal freedive, at 60 feet - even with a thin suit - I am pretty darn negative. I will be laying on the bottom to support myself and when I begin the ascent, I can feel being heavier than I like. The feeling is VERY different when using a neutral pony bottle which makes me a scuba diver and eliminates the chest crushing effect. In this video, you can see that when I start the ascent from 60 feet, I am actually neutral or maybe even floating up a little (positive buoyancy).

FYI. the solo dive is recorded from a gun mounted go pro which was left filming when the gun was wrapped up around a pole and "abandoned" during a freedive. The pony bottle was later used to make the recovery easier. A good freediver would have done it all on a breathhold.

[video=youtube;r-L9extLDZQ]http://www.youtube.com/watch?v=r-L9extLDZQ[/video]

I don't think I see the distinction....even with a 5 mil suit, at 70 to 90 feet, the freediver has no problem developing the power to swim off of the bottom....On a 90 foot drop, the freediver is likely to use just enough weight to be able to get down to 25 feet or so, before becoming near neutral and able to begin to fall... without wasting energy ---The real issue is not being too positively buoyant at the surface.... The Scuba Diver ---evil twin version, at 90 feet, with the same exact weighting as the freediver twin, is less negative due to full lungs at a foot off the bottom, and at most, they may use a few "puffs" of air into the wing.....but only creating a couple of pounds of lift...nothing major.
The weighting of the freediver works out very well for the scuba diver "evil twin", particularly with an Al 80 tank.


The scuba diver has virtually unlimited power at the surface to begin their descent with, unlike the freediver, so there is no real concern for the scuba diver in needing to expend a small amount of power to swim down the first 20 feet....after which they can fall downward, as does the freediver.

 

[ams511]

I'm really not interested in getting in a pissing match over all this. I was asked to give specific examples of WHY a diver might not want to be buoyant from a depth of 8 feet to the surface. Answer: I've know two people who have gotten whacked by boats on the surface while scuba diving, one I recovered from the bottom with prop marks exposing his brain and the other lost both legs below the knee. I'm not sure if buoyancy was an issue in either situation or not, but I would always want to have enough ballast to stop an ascent at any depth - even with an empty tank - since I am fearful of boats.

The statement was made that you can just figure the bouyancy of your suit at the surface and then have that much lift in the BC. So simple... I asked about the air in the tank and was pretty much ridiculed.

A simple analysis leads me to believe that air weight needs to be considered under this very simplistic assumption. The assumption that the cold water suit will lose 100% of the buoyancy at the surface is not something I have ever verified and to be honest, I would expect that some residual lift would remain at depth - possibly enough to account for some air in the tank.. but who knows? That is why I asked.

I am not trying to get into a pissing match either. It is a shame that boaters disregard the dive flag and that in Florida the Marine Patrol would rather ticket divers for not having a flag than ticking boaters for disregarding the flag. However, these accidents while tragic, have little to do with buoyancy. As Dan pointing out a diver could always kick down if a bit light.

The air in the tank and the weight of the tank gets taken into account when figuring out the weighting. Usually the recommendation is that the diver be able to hold a safety stop at 15 feet with a nearly empty tank. If you want to be heavier that is fine but this is done while calculating the weighting.

Once the weighting is determined then you are at the wing capacity stage. The wing needs to have enough lift to float the rig without the diver and to counteract the loss of buoyancy of the wetsuit at depth. You pick the greater of the two. Assuming a wetsuit losses its full capacity at depth, builds in a safety factor as well as keeping the math simple. A wetsuit does have residual lift at depth. How much lift depends on the depth of the dive and maybe the quality of the wetsuit material. I showed you the calculation in prior posts.

Lets assume the information in the your examples that the wetsuit is 25 lbs positive and that you need 30 lbs of lead with an Al-80. So you are carrying 30 lbs of lead and your tank and regulators are maybe another 4 lbs so your total is 34 lbs. If you carried all your weight in the BC pockets then you would need a 35 lb or larger wing to float the rig so that is the lift you need. If you carried it on your belt then your rig needs only 4 lbs to float and but your wetsuit could lose up to 25 lbs of lift so you are looking at a 25 or 30 lb wing. When people as for opinions I usually recommend a bit more lift than the minimum needed as a safety margin.

 

[dumpsterDiver]

I am not trying to get into a pissing match either. It is a shame that boaters disregard the dive flag and that in Florida the Marine Patrol would rather ticket divers for not having a flag than ticking boaters for disregarding the flag. However, these accidents while tragic, have little to do with buoyancy. As Dan pointing out a diver could always kick down if a bit light.

The air in the tank and the weight of the tank gets taken into account when figuring out the weighting. Usually the recommendation is that the diver be able to hold a safety stop at 15 feet with a nearly empty tank. If you want to be heavier that is fine but this is done while calculating the weighting.

Once the weighting is determined then you are at the wing capacity stage. The wing needs to have enough lift to float the rig without the diver and to counteract the loss of buoyancy of the wetsuit at depth. You pick the greater of the two. Assuming a wetsuit losses its full capacity at depth, builds in a safety factor as well as keeping the math simple. A wetsuit does have residual lift at depth. How much lift depends on the depth of the dive and maybe the quality of the wetsuit material. I showed you the calculation in prior posts.

Lets assume the information in the your examples that the wetsuit is 25 lbs positive and that you need 30 lbs of lead with an Al-80. So you are carrying 30 lbs of lead and your tank and regulators are maybe another 4 lbs so your total is 34 lbs. If you carried all your weight in the BC pockets then you would need a 35 lb or larger wing to float the rig so that is the lift you need. If you carried it on your belt then your rig needs only 4 lbs to float and but your wetsuit could lose up to 25 lbs of lift so you are looking at a 25 or 30 lb wing. When people as for opinions I usually recommend a bit more lift than the minimum needed as a safety margin.

I'm not sure how you could determine weighting and bouyancy were not factors in the accidents. I know one guy who flipped and sprinted down and the props chipped his fins, while the other guy was not so lucky and got both legs chopped at the shins. It is a good enough example for me to not want to be popping to the surface with an empty tank, if I can avoid it.

I understand that the incomplete suit compression probably offsets the air weight for a typical recreational, single tank. That would probably have been a better answer than some of the other responses..

 

[danvolker]

I'm not sure how you could determine weighting and bouyancy were not factors in the accidents. I know one guy who flipped and sprinted down and the props chipped his fins, while the other guy was not so lucky and got both legs chopped at the shins. It is a good enough example for me to not want to be popping to the surface with an empty tank, if I can avoid it.

I understand that the incomplete suit compression probably offsets the air weight for a typical recreational, single tank. That would probably have been a better answer than some of the other responses..

Dumpster, the picture you just painted, was one where the divers came up into the props of a boat going overhead. This was caused by divers surfacing where/when they should not, and had they been surfacing by their flag under the protection of a Dive Charter operator, the charter boat would have stood off any incoming boats. And even in this scenario, with the divers with a good charter boat, they need to be able to hold a stop --as a skill any diver should have. I don't think you are saying they were not heavy enough to hold a stop--it sounds like you are saying they came up when they should not have, and could not get back down quickly enough. The fix for this is not being crazy negative...the fix is not coming up when and where you should not.

This is also a huge downside to diving off of private boats, where most have no one running the boat that is capable of protecting divers with the skill of the charter boat captains....not to mention a TINY private boat, is not going to be very good at scaring off a drunk running a 50 foot booze crusier or sport fish.

 

[Yoyodyne-88]

"...the picture you just painted, was one where the divers came up into the props of a boat going overhead. This was caused by divers surfacing where/when they should not, and had they been surfacing by their flag under the protection of a Dive Charter operator, the charter boat would have stood off any incoming boats."

That is absolutely not the real world, at least not where I dive.

I have personally watched large lobster boats run down dive flags, and knowingly manuever directly over groups of dive students, despite onlookers at the surface screaming at them.

In another case, a speedboat ran right between the dive charter boats, despite dive flags flying and crew waving them off. A diver was struck in the head and killed (while surfacing exactly where he should have been. The boater saw the blood in the water and took off - and was never identified or caught.

As for a "head down and kicking" stop, I have seen too many new divers make totally uncontrolled ascents to the surface in exactly that manner. And a drysuit diver in that position cannot vent their suit.

You are espousing very dangerous ideas, to defend an unneccessarily contrarian and ego-laden position. One not based in reality.

Or maybe South Florida is different.

 

[cool_hardware52]

"...the picture you just painted, was one where the divers came up into the props of a boat going overhead. This was caused by divers surfacing where/when they should not, and had they been surfacing by their flag under the protection of a Dive Charter operator, the charter boat would have stood off any incoming boats."

That is absolutely not the real world, at least not where I dive.

I have personally watched large lobster boats run down dive flags, and knowingly manuever directly over groups of dive students, despite onlookers at the surface screaming at them.

In another case, a speedboat ran right between the dive charter boats, despite dive flags flying and crew waving them off. A diver was struck in the head and killed (while surfacing exactly where he should have been. The boater saw the blood in the water and took off - and was never identified or caught.

As for a "head down and kicking" stop, I have seen too many new divers make totally uncontrolled ascents to the surface in exactly that manner. And a drysuit diver in that position cannot vent their suit.

You are espousing very dangerous ideas, to defend an unneccessarily contrarian and ego-laden position. One not based in reality.

Or maybe South Florida is different.

I've seen all sorts of divers "cork" uncontrollably, even those I would consider grossly over weighted. IME overweighting leads to more difficult buoyancy control, the required "bubble" in the BC is bigger.

Are you arguing that if a diver becomes couple pounds positive after leaving their safety stop they can't stop an unwanted ascent? They can't exhale, flare and swim down 2-3 lbs? Really?


Tobin

 

[danvolker]

"...the picture you just painted, was one where the divers came up into the props of a boat going overhead. This was caused by divers surfacing where/when they should not, and had they been surfacing by their flag under the protection of a Dive Charter operator, the charter boat would have stood off any incoming boats."

That is absolutely not the real world, at least not where I dive.

I have personally watched large lobster boats run down dive flags, and knowingly manuever directly over groups of dive students, despite onlookers at the surface screaming at them.

In another case, a speedboat ran right between the dive charter boats, despite dive flags flying and crew waving them off. A diver was struck in the head and killed (while surfacing exactly where he should have been. The boater saw the blood in the water and took off - and was never identified or caught.

As for a "head down and kicking" stop, I have seen too many new divers make totally uncontrolled ascents to the surface in exactly that manner. And a drysuit diver in that position cannot vent their suit.

You are espousing very dangerous ideas, to defend an unneccessarily contrarian and ego-laden position. One not based in reality.

Or maybe South Florida is different.

First, we are talking about wetsuit diving, not dry suit....

Where you talk about the boat carnage, and students being ignored by speeding boaters....weighting your divers heavy to protect them from this would be a foolish solution to the problem.
I would suggest you find places ( reefs or wrecks) to dive without this dangerous traffic, get Captains on the boat you use that do not anchor during dives, and instead--stay vigilant, and are good at positioning their boat between the divers in their charge, and any incoming boats on a strafing run over your divers ( all the drift diving charter boats in Palm Beach do this--they are always ready to fend off a drunken boater, and they would NEVER just watch in horror and let a speed boat run over their divers)...

Your issue with overweighting your divers has much bigger problems....While the stop may be effortless for them, should they ever experience a BC or wing failure, they are overweighted---and are suddenly in danger of drowning.

As the picture you are painting is of novice types unable to think for themselves ( happy to ascend directly upwards into the props of boaters they should hear running toward them) , almost every day they are out diving, the extra weight they would be wearing, has them diving with large bubbles and poor control of buoyancy, and lumbering along with little control of their movement in any direction.

I would prefer to make students that move around easily like fish, that think before they surface, and that have perfect control. This means a wetsuit that is not ridiculously buoyant, a small wing/bc ( to prevent the issue of large bubble) that is matched to the buoyancy swings of the wetsuit, with a functional Maximum Operating Depth understood for the wetsuit with this wing/bc....just as with nitrox.

And as for your "head down and kicking" comment.....
In this discussion, we are talking about a possible positive buoyancy of a couple of pounds.
....Neither I nor any instructor friend of mine, has taught students to use a BC as an elevator...they swim up, or swim down.
At 20 feet, the wing /bc would be used at the stop to achieve a neutral buoyancy if possible....( and remember, the freediver is positive on the surface, but becomes about neutral at 20 to 30 feet)...but this is a nicety. Swimming/propulsion is the far more important skill, it is the skill that gets the diver up or down, and for many miles horizontally when desired. If you teach a student to fin-swim properly, holding a 20 foot stop will be very easy for them. Remember, they were able to SWIM DOWN at the beginning of the dive, and the tank is just a couple pounds lighter....often balanced a bit by a wetsuit that has LOST some of it's inherent buoyancy from compression at depth.

We are having this discussion, because SO MANY dive shops churn out huge classes of Groupon style , under-instructed students, and in the rush to get these masses certified, the NORMATIVE behavior of this type of shop, is to give each student "PLENTY OF WEIGHT" so that they can easily get the whole class standing or kneeling on the bottom....and not have to spend 30 minutes ON EACH STUDENT, finding perfect weighting....These shops just will never do that...too much time, too much expense for a volume class. The solution, overweighting, also allows sale of big BC's/wings, and bigger, more expensive tanks, that have enough air to allow the extra work of pushing the huge pufferfish diver through the water.