Does this BC product exist?
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Wow -- What an extremely cool thing, that the person who did the research is chiming in here. Steve, I may not speak for everybody, but I for one would be very interested to read anything you have to say on this subject. It would be so much more valuable than simple personal opinions, of which we have an overabundance on this subject 
StevenPaulet
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Alright, I'll pull some thoughts together on this. I'm sure nobody wants the thesis rewritten here, but there are some good pertinent and topical relevant info I can add, and clarify the thoughts on that body of work done in the 80's.
And as Dave Mclain's (I mispell his name on purpose since he mispelled mine, LOL) powerpoint shows, not much has really changed, so much of the work, if not all of it, would stand today. I'm glad to see Dave's History of the BC powerpoint up, as that will be a good reference starting point. And even thought Dave is a long-time friend, I will say that nobody is better to write that history than him. He was a big part of it.
I'll gather and summarize some thoughts here later tonight or so. Many of the papers written and presented on this exist on IEEE's site as they were presented at Oceans, and NAUI IQ, and AAUS in the mid-late 80's.
I currently don't have any of this in digital form, but I can scan it and post it for reference. Oh how my wife is going to hate this getting in the way of her honey do list. Worst case, tommorrow!
Steve Paulet (one t, no e.)
And as Dave Mclain's (I mispell his name on purpose since he mispelled mine, LOL) powerpoint shows, not much has really changed, so much of the work, if not all of it, would stand today. I'm glad to see Dave's History of the BC powerpoint up, as that will be a good reference starting point. And even thought Dave is a long-time friend, I will say that nobody is better to write that history than him. He was a big part of it.
I'll gather and summarize some thoughts here later tonight or so. Many of the papers written and presented on this exist on IEEE's site as they were presented at Oceans, and NAUI IQ, and AAUS in the mid-late 80's.
I currently don't have any of this in digital form, but I can scan it and post it for reference. Oh how my wife is going to hate this getting in the way of her honey do list. Worst case, tommorrow!
Steve Paulet (one t, no e.)
You know I would not hgesitate to say that an old Scubabpro classic BC on a diver with proper weighting (thus no excess of air in BC) has less drag than a BP/W.
asckar
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Try the Oceanic Outrigger. I believe it has the type of technology you're looking for.
dk2943
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When I got my back inflator, I was told to simply lean back a little when on the surface
StevenPaulet
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Ok, before I go off and scan and post some of the work done that was referenced I'll just lay down some thoughts from what little I read.
No, I'm not going to read through 10 pages yet. I'll save that for later in the week, and then digest it and address what I might agree with, disagree with, or add to what needs to be said.
The issue my research referenced was Hydrodynamic Drag of Scuba Divers. It was a project I started back in 1985 while a dive instructor at the University of Rhode Island scientific diving courses.
A few issues were predominent then, and were topics of debate. And we sought rhyme and reason, which forged the research I'll comment on. Some of the issues/challenges/observations we wanted to investigate:
- BCD design and implications on drag - energy expelled.
- Factors relating to Human Underwater Performance and safety.
- Propulsion vs form and surface drag.
(ok, there were more but I'll have to look them up).
I was motivated for this work by watching students and other divers in puzzling situations: plowing through the surface with a full horsecollar bcd, overweighted divers with huge underwater jacket bcd's plowing through the water, sustainability of operating in strong currents, etc.
The issue of hydrodynamic drag on scuba divers is a large undertaking as we soon found out. What we didn't want to get into was "which is the best BCD on the market". Instead, we wanted to quantify drag and it's impications on effort and safety.
It's clear that if you double the area exposed underwater, the effort to overcome that is 4 times, and triple the area, and it will now take 9 times the energy/effort... ie, its a squared relationship.
Empirical analysis of the issues give a little insight into the expected results, but as I said, we wanted to quantify it. And in the beginning of the project, we had visions of completely analyzing/profiling BCD's for many manufactures. We contacted over a dozen manufacturers to participate, and almost all of them donated BCD's to be tested.
From 1985-1987 we were given over 50 BCD's to test, and the technology and designs at that time are really no different that what is available today. Reference Dave McLean's History of the BCDs and you'll find this to be true.
I had several jacket type BCD's (Scubapro Stab Jacket, Dacor, Seatec, Seaquest, USD). These were full sized jackets.
I had several horsecollar style BCD's to test and compare (Fenzy, USD, Seaquest)
I also had several of the integrated hard shell systems from Scubapro, USD, atpack, and others that will come to mind later on.
What showed great promise and interest was the recent developments of the smaller, slimline designs from Seatec (Manta), Seaquest (ADV), and a few other companies prototypes.
I always felt that the ADV design was the right thing to do, in putting the air from the BCD system under the arms instead of over the shoulders. I'm sure those who have looked at this problem would agree. Reduce the exposure and aspect of volume and you will reduce your drag.
I also had several "wing" type BCD's to test. I had one from Seatec, and one from (somebody help me out here.... techdiving outfit, it alludes me right this second.). Some with integrated weight systems.
Many at the time thought that the wing BCD's were the lowest drag, and we just had to test that. And of course, many old timers thought the Fenzy horsecollar was going to be the clear low drag unit.
I also have to add one design factor I was testing. Construction. By that I mean, most BCD's were going from the single bladder design (Fenzy, Stab Jacket), to double bladder where you have a vinyl type bladder wrapped by a ballistic nylon protective material.
What I noticed long before this project was that the double bladder design held an incredible amount of water (ever lift your BCD out of the water, and watch all the water fall out), while single bags just pulled out and only surface water flushed about. This had a few implications. But the one that showed the most promise was the momentum factor. If you are carrying that much water around with you, its not a drag force anymore, but a mass issue. And since divers swim in a start/move/stop/move fashion, and not always a constant motion, and this "carrying extra water" is a huge effort.
So, we looked at testing designs not only in form, but in construction.
Now, testing drag on a scuba diver is an exercise in futility. I saw studies that were done by draging a diver on a tether, but the drum measurements were not accurate, nor did they account for the "windings". Plus, this method allowed the diver to flop around in all sorts of angles.
Angles.
The angle of attack of the diver through the water was perhaps the single biggest factor in drag measurements. I designed an apperatus that held the diver constant as he moved through the water, and allowed us to vary his angle of progression/attack through the water. Tilt the diver up 10% and you will see his "frontal area" increase, and the resulting drag increase squared... ie, more significantly.
So, when "profiling" a certain BCD, you had to analyze how it made you swim through the water, and test it that way.
Inflation level.
Test the BCD totally empty, you get one result. Put in 10 lbs of buoyancy and the BCD's all start becoming a different animal underwater... varying where they put that air.
So, there were a lot of factors to look at while testing. A book can be written on each and every BCD, looking at angles of diver incidence, inflation levels at depth and on the surface.
Note that when we approached the BCD manufacturers with preliminary results on their designs and asked for some minor funding to completely "profile" their BCD for safety and human performance... they punted. They were more interested in color, sizing, and other market issues. Their designs were set and they had no interest in modifying them to make them safer.
We continued to test and profile many BCD's, as I did lend a good bit of consulting information to a few manufacturers, and of course, the Navy was interested and funded a good bit of the study.
The benefits of streamlining your equipment are many. Obviously you don't want to snag anything on the environment, boat or buddies. But the biggest benefit is that of safety, by way of conserving energy. People dive till they are tired or out of air, or out of time. Generally, they wait till they are out of air/time, and come up. And then its a matter of how much energy/strength they have to come back to the boat/shore. And in the case of being an instructor, how much energy/strength you have to assist students.
Ever dive in cold water? Its the single biggest robber of strength and energy, and every little bit saved, the better. Undertaking this study in Rhode Island had meaning to several of us.
A quick note about our testing apperatus. I was fortunate to have access to a very high tech wave and tow tank. The tank was used to test many ocean engineering parameters in marine designs... offshore platforms, shipbuilding, etc. I used the towing and drag measuring feature. This allowed me to pull a diver through the water at various and well controlled speeds, angles, depths, and measure to high accuracy the drag forces involved. I can go on and on about defending the feasibility and accuracy of this testing system, but it was built and funded by some of the largest companies and their engineering departments. I was fortunate enough to find out that it was perfect for this purpose. More important than the results of the BCDs in this project, was the testing procedures.
So, what's the best BCD?
Yeah, as if I was going to go there.
I will state a few findings. Many of these were distributed and published for manufacturing consumption and many will claim they listened, and reacted.
Construction.
I found a critical issue in construction where if the manufacturer did not incorporate a good way to compress the outer nylon bag around the bladder, it carried too much water and the "inertia" involved in diving with that much water, each and every stop and go kick, was significant. It was then manufacturers started using compressible bladder/outer bag designs... or better yet, single bag designs with a well meaning purpose.
Design.
Quite frankly, its obvious now, but it wasn't to the manufacturers then. The SeaQuest ADV was a tremendous trendsetter in design, but it was designed that way to facilitate using the BDC with a drysuit. Along they way, they realized the buoyancy was now hidden under the arm, and along the tank. Perfect for low drag diving.
The design of the BCD empty and with air (at depth) was critical. Where does the air go? It was obvious that most manufacturers back then didn't care. The BDC was designed to float you at the surface (some kept your head up, others slammed your face down). Only a few did a good job of doing all the things that BCD's where supposed to do. Float you on the surface before and after the dive, allow decent buoyancy control at depth, keep the air from expanding your frontal projection. But they were a few.
I'll outline a few thoughts on a few general designs.
(cont...)
No, I'm not going to read through 10 pages yet. I'll save that for later in the week, and then digest it and address what I might agree with, disagree with, or add to what needs to be said.
The issue my research referenced was Hydrodynamic Drag of Scuba Divers. It was a project I started back in 1985 while a dive instructor at the University of Rhode Island scientific diving courses.
A few issues were predominent then, and were topics of debate. And we sought rhyme and reason, which forged the research I'll comment on. Some of the issues/challenges/observations we wanted to investigate:
- BCD design and implications on drag - energy expelled.
- Factors relating to Human Underwater Performance and safety.
- Propulsion vs form and surface drag.
(ok, there were more but I'll have to look them up).
I was motivated for this work by watching students and other divers in puzzling situations: plowing through the surface with a full horsecollar bcd, overweighted divers with huge underwater jacket bcd's plowing through the water, sustainability of operating in strong currents, etc.
The issue of hydrodynamic drag on scuba divers is a large undertaking as we soon found out. What we didn't want to get into was "which is the best BCD on the market". Instead, we wanted to quantify drag and it's impications on effort and safety.
It's clear that if you double the area exposed underwater, the effort to overcome that is 4 times, and triple the area, and it will now take 9 times the energy/effort... ie, its a squared relationship.
Empirical analysis of the issues give a little insight into the expected results, but as I said, we wanted to quantify it. And in the beginning of the project, we had visions of completely analyzing/profiling BCD's for many manufactures. We contacted over a dozen manufacturers to participate, and almost all of them donated BCD's to be tested.
From 1985-1987 we were given over 50 BCD's to test, and the technology and designs at that time are really no different that what is available today. Reference Dave McLean's History of the BCDs and you'll find this to be true.
I had several jacket type BCD's (Scubapro Stab Jacket, Dacor, Seatec, Seaquest, USD). These were full sized jackets.
I had several horsecollar style BCD's to test and compare (Fenzy, USD, Seaquest)
I also had several of the integrated hard shell systems from Scubapro, USD, atpack, and others that will come to mind later on.
What showed great promise and interest was the recent developments of the smaller, slimline designs from Seatec (Manta), Seaquest (ADV), and a few other companies prototypes.
I always felt that the ADV design was the right thing to do, in putting the air from the BCD system under the arms instead of over the shoulders. I'm sure those who have looked at this problem would agree. Reduce the exposure and aspect of volume and you will reduce your drag.
I also had several "wing" type BCD's to test. I had one from Seatec, and one from (somebody help me out here.... techdiving outfit, it alludes me right this second.). Some with integrated weight systems.
Many at the time thought that the wing BCD's were the lowest drag, and we just had to test that. And of course, many old timers thought the Fenzy horsecollar was going to be the clear low drag unit.
I also have to add one design factor I was testing. Construction. By that I mean, most BCD's were going from the single bladder design (Fenzy, Stab Jacket), to double bladder where you have a vinyl type bladder wrapped by a ballistic nylon protective material.
What I noticed long before this project was that the double bladder design held an incredible amount of water (ever lift your BCD out of the water, and watch all the water fall out), while single bags just pulled out and only surface water flushed about. This had a few implications. But the one that showed the most promise was the momentum factor. If you are carrying that much water around with you, its not a drag force anymore, but a mass issue. And since divers swim in a start/move/stop/move fashion, and not always a constant motion, and this "carrying extra water" is a huge effort.
So, we looked at testing designs not only in form, but in construction.
Now, testing drag on a scuba diver is an exercise in futility. I saw studies that were done by draging a diver on a tether, but the drum measurements were not accurate, nor did they account for the "windings". Plus, this method allowed the diver to flop around in all sorts of angles.
Angles.
The angle of attack of the diver through the water was perhaps the single biggest factor in drag measurements. I designed an apperatus that held the diver constant as he moved through the water, and allowed us to vary his angle of progression/attack through the water. Tilt the diver up 10% and you will see his "frontal area" increase, and the resulting drag increase squared... ie, more significantly.
So, when "profiling" a certain BCD, you had to analyze how it made you swim through the water, and test it that way.
Inflation level.
Test the BCD totally empty, you get one result. Put in 10 lbs of buoyancy and the BCD's all start becoming a different animal underwater... varying where they put that air.
So, there were a lot of factors to look at while testing. A book can be written on each and every BCD, looking at angles of diver incidence, inflation levels at depth and on the surface.
Note that when we approached the BCD manufacturers with preliminary results on their designs and asked for some minor funding to completely "profile" their BCD for safety and human performance... they punted. They were more interested in color, sizing, and other market issues. Their designs were set and they had no interest in modifying them to make them safer.
We continued to test and profile many BCD's, as I did lend a good bit of consulting information to a few manufacturers, and of course, the Navy was interested and funded a good bit of the study.
The benefits of streamlining your equipment are many. Obviously you don't want to snag anything on the environment, boat or buddies. But the biggest benefit is that of safety, by way of conserving energy. People dive till they are tired or out of air, or out of time. Generally, they wait till they are out of air/time, and come up. And then its a matter of how much energy/strength they have to come back to the boat/shore. And in the case of being an instructor, how much energy/strength you have to assist students.
Ever dive in cold water? Its the single biggest robber of strength and energy, and every little bit saved, the better. Undertaking this study in Rhode Island had meaning to several of us.
A quick note about our testing apperatus. I was fortunate to have access to a very high tech wave and tow tank. The tank was used to test many ocean engineering parameters in marine designs... offshore platforms, shipbuilding, etc. I used the towing and drag measuring feature. This allowed me to pull a diver through the water at various and well controlled speeds, angles, depths, and measure to high accuracy the drag forces involved. I can go on and on about defending the feasibility and accuracy of this testing system, but it was built and funded by some of the largest companies and their engineering departments. I was fortunate enough to find out that it was perfect for this purpose. More important than the results of the BCDs in this project, was the testing procedures.
So, what's the best BCD?
Yeah, as if I was going to go there.
I will state a few findings. Many of these were distributed and published for manufacturing consumption and many will claim they listened, and reacted.
Construction.
I found a critical issue in construction where if the manufacturer did not incorporate a good way to compress the outer nylon bag around the bladder, it carried too much water and the "inertia" involved in diving with that much water, each and every stop and go kick, was significant. It was then manufacturers started using compressible bladder/outer bag designs... or better yet, single bag designs with a well meaning purpose.
Design.
Quite frankly, its obvious now, but it wasn't to the manufacturers then. The SeaQuest ADV was a tremendous trendsetter in design, but it was designed that way to facilitate using the BDC with a drysuit. Along they way, they realized the buoyancy was now hidden under the arm, and along the tank. Perfect for low drag diving.
The design of the BCD empty and with air (at depth) was critical. Where does the air go? It was obvious that most manufacturers back then didn't care. The BDC was designed to float you at the surface (some kept your head up, others slammed your face down). Only a few did a good job of doing all the things that BCD's where supposed to do. Float you on the surface before and after the dive, allow decent buoyancy control at depth, keep the air from expanding your frontal projection. But they were a few.
I'll outline a few thoughts on a few general designs.
(cont...)
StevenPaulet
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(cont...)
Horsecollar.
Deflated, these aren't bad. The Fenzy when fit right, rides flat against you. But many other "flap around", carry water between the bags, between the BCD and diver.
Inflated, the horsecollar was a snowplow. A little air pulled the divers angle up, and then sat air on the chest. This just worsened with additional inflation. What we did back in the day was make sure our BCD's didn't need air at depth... but that was called "training", and not something you pick up on a DVD nowadays.
On the surface, the fully inflated horsecollars were again a snowplow. High drag, and one of the motivating factors for the study. I knew there had to be a better way.
SeaJackets... Full size Jackets, Stabilizer Jackets.
Deflated, these were still huge and clingy underwater. They carried water between their double bags if constructed that way, AND they carried a lot of water between the BDC and the diver.
Inflated, put a little air in these jackets, and that air flops around the tank and shoulders and starts to drastically increase the frontal projection of the diver, significantly increasing the drag.
On the surface, these jackets were horrible, with all the air up over the shoulders, jetting out of the water, over and above the diver. As we know, air in a BCD works better if its in the water, pushing you up, but this was a huge waste.
ADV, "low profile" types.
Deflated, these vests were designed to fit "snugger". It should go without saying that they are low profile to start, hence less drag.
Inflated, these were designed to be better inflated. They tend to hide the air under the arms, tightly along the tank. Underwater, these zip along. Add a little air, its hidden well, add more, its still good. It keeps the diver trimmed well to continue to zip through the water, and this is where many designs fail in that they change that attitude of the diver and angle them up... bad for ergonomics and drag.
On the surface, these ADV designs were great, boosting you out of the water higher than most, since all the air was under the diver at the water, as opposed to out of the water. Making way and swimming through the water with a fully inflated ADV design BCD was also less drag than most.
Wing type BCD's.
Deflated, many of these were not that great because the deflated wings would drag/flap. I know subsequent years and designs allowed for these wings to be pulled in with elastic. But if they aren't fully retracted, these wings still do more to hinder swiming than act as wings to fly.
Inflated. Ugh, this is where they started to flounder. Wings pulled the diver up, increased their angle in the water, and this drastically increased drag/effort. Now, if you are drift diving, who cares, but these units curl you up, and you have to kick against it.
On the surface, well, one of the biggest problems is floating safely on the surface without being tilted forward. And then swimming on the surface is an effort as it pushes you into the water. It takes getting used to, but you have the trade-off on floating on the surface, or being pushed into the water.
Hardpacks - Integrated units.
Ok, inflated/deflated these obviously didn't change shape, but they carried a ton of water. The inertial forces were predominent. And then these floated you much like a wing BCD with the floatation on your back, tilting you forward on your face.
So, here are a few generalities to keep in mind. If you want low drag, keep your diving system "low profile". Either learn to dive without air in your BCD, or have a BCD that keeps the air from expanding your frontal area projection. We found the ADV designs (that are exactly like the current style low profile BCD's) to be the best happy mediums. Single bag type designs are better than double, but double will be a part of our life because of the manufacturing and cost issues.
Find a BCD that is low in profile (inflated and deflated), carries little water in itself, in its construction, and in its design (between BCD and diver), keeps the diver floating well at the surface, and keeps the diver horizontal as possible with many levels of inflation while at depth... and you have a winner. So, as you can see, most of the BCD designs were represented, new and old. Choose another design type, and you have to learn to live with it's shortcomings.
Did I really just ramble on like that? Ok, I apologize. Probably should have done that in the beginning. But maybe now I don't have to dig though my basement for the box that holds all the data sheets, images and start a blog on this.
So ok, where were we?
LOL.
Horsecollar.
Deflated, these aren't bad. The Fenzy when fit right, rides flat against you. But many other "flap around", carry water between the bags, between the BCD and diver.
Inflated, the horsecollar was a snowplow. A little air pulled the divers angle up, and then sat air on the chest. This just worsened with additional inflation. What we did back in the day was make sure our BCD's didn't need air at depth... but that was called "training", and not something you pick up on a DVD nowadays.
On the surface, the fully inflated horsecollars were again a snowplow. High drag, and one of the motivating factors for the study. I knew there had to be a better way.
SeaJackets... Full size Jackets, Stabilizer Jackets.
Deflated, these were still huge and clingy underwater. They carried water between their double bags if constructed that way, AND they carried a lot of water between the BDC and the diver.
Inflated, put a little air in these jackets, and that air flops around the tank and shoulders and starts to drastically increase the frontal projection of the diver, significantly increasing the drag.
On the surface, these jackets were horrible, with all the air up over the shoulders, jetting out of the water, over and above the diver. As we know, air in a BCD works better if its in the water, pushing you up, but this was a huge waste.
ADV, "low profile" types.
Deflated, these vests were designed to fit "snugger". It should go without saying that they are low profile to start, hence less drag.
Inflated, these were designed to be better inflated. They tend to hide the air under the arms, tightly along the tank. Underwater, these zip along. Add a little air, its hidden well, add more, its still good. It keeps the diver trimmed well to continue to zip through the water, and this is where many designs fail in that they change that attitude of the diver and angle them up... bad for ergonomics and drag.
On the surface, these ADV designs were great, boosting you out of the water higher than most, since all the air was under the diver at the water, as opposed to out of the water. Making way and swimming through the water with a fully inflated ADV design BCD was also less drag than most.
Wing type BCD's.
Deflated, many of these were not that great because the deflated wings would drag/flap. I know subsequent years and designs allowed for these wings to be pulled in with elastic. But if they aren't fully retracted, these wings still do more to hinder swiming than act as wings to fly.
Inflated. Ugh, this is where they started to flounder. Wings pulled the diver up, increased their angle in the water, and this drastically increased drag/effort. Now, if you are drift diving, who cares, but these units curl you up, and you have to kick against it.
On the surface, well, one of the biggest problems is floating safely on the surface without being tilted forward. And then swimming on the surface is an effort as it pushes you into the water. It takes getting used to, but you have the trade-off on floating on the surface, or being pushed into the water.
Hardpacks - Integrated units.
Ok, inflated/deflated these obviously didn't change shape, but they carried a ton of water. The inertial forces were predominent. And then these floated you much like a wing BCD with the floatation on your back, tilting you forward on your face.
So, here are a few generalities to keep in mind. If you want low drag, keep your diving system "low profile". Either learn to dive without air in your BCD, or have a BCD that keeps the air from expanding your frontal area projection. We found the ADV designs (that are exactly like the current style low profile BCD's) to be the best happy mediums. Single bag type designs are better than double, but double will be a part of our life because of the manufacturing and cost issues.
Find a BCD that is low in profile (inflated and deflated), carries little water in itself, in its construction, and in its design (between BCD and diver), keeps the diver floating well at the surface, and keeps the diver horizontal as possible with many levels of inflation while at depth... and you have a winner. So, as you can see, most of the BCD designs were represented, new and old. Choose another design type, and you have to learn to live with it's shortcomings.
Did I really just ramble on like that? Ok, I apologize. Probably should have done that in the beginning. But maybe now I don't have to dig though my basement for the box that holds all the data sheets, images and start a blog on this.
So ok, where were we?
LOL.
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