Best Jacket Style BC with Tech Options

[Eric Sedletzky]

The work was done, years ago, by someone who occasionally drops by ScubaBoard and was published (if I remember correctly) in one of the IEEE "Oceans" volumes. Going from memory, the lowest drag was the FENZY and the highest drag was a WaterGil (ATPac) wing style, it was thought that the "flapping" of the deflated wing was what raised the drag. This project lead to the design of the ADVi, the progenitor of all the current BCDs and a very low drag design that has since been compromised by hanging on lots of doo-dads,

I actually would like to see a new study testing new gear. Gear has changed in shape since those days. Maybe the concept has remained the same but certain styling and weight integration has become the norm. It may be my personal feeling but I don't really think companies who manufature jacket BC's or all in one units are really concerned with things like trim or streamlining.
If it just so happens that their product slipstreams pretty well I think it would be a secondary by product to comfort on the showroom floor and flashy features.
I still like my drag test idea dressing up a neutrally buoyant dummy in all the latest BC's including BP/W and putting it into an endless pool at different water speeds and measuring drag in the form of weight resistance with a fish scale attached to a ring in the center of the dummies head.

 

[Thalassamania]

...
There should be a special class just on CG, overall weighting, weight breakidown and distribution, and exposure protection options and weighting in accordance with said options.
Too many instructors let all this go because they either don't know the information themselves, or don't have time to deal with it. However it is one of the most important concepts in diving a student really needs to know and not just leave it willy nilly.

There are entry level courses that include such an analysis and that include exercises to aid in learning and retention. There have been such courses (that I know of) since the early 1960s. I specifically remember sitting in on a lecture by Bob Titchnell at San Jose State in the spring of 1968 (I had a GF in the class) and he talked about breath control and weightbelt movement, as they relate to trim in the water. This was not a science class, just a 40 hour NAUI recreational course in the PE Dept.

Note from another thread: Some folks (I am one, Grateful Diver is another) find it easier to trim pitch and roll precisely using a dry suit:

Oddly, I have better buoyancy control in a drysuit and heavy undergarment than I do in a 2/3 wetsuit. Then again, I have about 2500 more dives in a drysuit than I do in a 2/3 wetsuit ... skills really are relative to what you're used to ...

... Bob (Grateful Diver)

I don't find that odd at all, a good drysuit lets you establish a highly stable tripod (across the back and each leg) that you can balance like a ballet diver, both pitch and roll ... much harder to do in a wetsuit where you can not readjust your center of buoyancy except by breath control and moving your weightbelt up and down.

 

[-hh]

Your explanation is a good one, but misses two potential "adjustments." The first is the diver's lungs, changing the midpoint of breathing can have a large effect on the CP. The same thing is true for a weightbelt, moving it for and aft makes the same sort of change, that's my problem with most BCDs, they inhibit the possible movement of the belt. Most of the fis-fuddle (for most non-dry suit divers) about trim can be replaced with a little knowledge and practice with just these two variables.

Good points on both, although I don't necessarily see a big contribution from lung control for changing trim while a surface float, per se.

Of course, when we mention the art of weightbelt weight placement, we also have to acknowledge that the 'modernization' has been the weight integrated BCDs, and their main pouches are generally located on the front of hips, which (unlike a good weightbelt setup) leaves the small of the back vacant, thereby shifting the load forward (ventral).

I actually would like to see a new study testing new gear. Gear has changed in shape since those days. Maybe the concept has remained the same but certain styling and weight integration has become the norm. It may be my personal feeling but I don't really think companies who manufature jacket BC's or all in one units are really concerned with things like trim or streamlining.

Probably not. I noticed that one of the BCs I checked out this weekend had what appeared to be good looking pockets, but while I was doing a quick (dry) test wear, I'm not sure that I'd actually be able to articulate my hand to actually reach some of its pockets. A lot of good that would do! It's going to require a test dive to really check this one out...hoping it was merely positional.

If it just so happens that their product slipstreams pretty well I think it would be a secondary by product to comfort on the showroom floor and flashy features.
I still like my drag test idea dressing up a neutrally buoyant dummy in all the latest BC's including BP/W and putting it into an endless pool at different water speeds and measuring drag in the form of weight resistance with a fish scale attached to a ring in the center of the dummies head.

There's more than one way to skin a cat to get the data Locally to me, Stevens Institute of Technology has the Davidson Laboratory towing tank, which is specifically to measure hydrodynamic performance (and looks big enough to do this on 1:1 scale). I used to have an affiliate with contacts there, but I haven't talked to him in years. In any case, what would be a fairly easy thing for us to do would be to offer to resource it as an Engineering Senior Design project and let an undergraduate team go figure out and do the work as a learning opportunity.


-hh

 

[Thalassamania]

Good points on both, although I don't necessarily see a big contribution from lung control for changing trim while a surface float, per se.

I can shift about eight lbs without even thinking about it, about 15 lbs with some discomfort ... trust me, that will change your center of buoyancy.

Of course, when we mention the art of weightbelt weight placement, we also have to acknowledge that the 'modernization' has been the weight integrated BCDs, and their main pouches are generally located on the front of hips, which (unlike a good weightbelt setup) leaves the small of the back vacant, thereby shifting the load forward (ventral).

Just one more reason to get rid of weight integrated BCs, modernity is not always congruent with utility.

Probably not. I noticed that one of the BCs I checked out this weekend had what appeared to be good looking pockets, but while I was doing a quick (dry) test wear, I'm not sure that I'd actually be able to articulate my hand to actually reach some of its pockets. A lot of good that would do! It's going to require a test dive to really check this one out...hoping it was merely positional.

There's more than one way to skin a cat to get the data Locally to me, Stevens Institute of Technology has the Davidson Laboratory towing tank, which is specifically to measure hydrodynamic performance (and looks big enough to do this on 1:1 scale). I used to have an affiliate with contacts there, but I haven't talked to him in years. In any case, what would be a fairly easy thing for us to do would be to offer to resource it as an Engineering Senior Design project and let an undergraduate team go figure out and do the work as a learning opportunity.

-hh

I actually would like to see a new study testing new gear. Gear has changed in shape since those days. Maybe the concept has remained the same but certain styling and weight integration has become the norm. It may be my personal feeling but I don't really think companies who manufature jacket BC's or all in one units are really concerned with things like trim or streamlining.
If it just so happens that their product slipstreams pretty well I think it would be a secondary by product to comfort on the showroom floor and flashy features.
I still like my drag test idea dressing up a neutrally buoyant dummy in all the latest BC's including BP/W and putting it into an endless pool at different water speeds and measuring drag in the form of weight resistance with a fish scale attached to a ring in the center of the dummies head.

I'd love to see a new study, the problem is first of all access to a tow tank (which I had), second of all some interested students (there were two who were scientific diving instructors,Steven Paulet and Shannon Byrne, in my program and who needed senior Ocean Engineering research topics) and thirdly a supply of many different BC designs for testing, which were generously provided by the R&D Director of a major BC manufacturer, David McLean who had more than a passing interest in the outcome, which revolutionized BC design. Three unsung heroes of diving who should be remembered.

Working against this is the attitude of most of the manufacturers that unproven claims and "style" should overcome truth and testing.

 

[-hh]

Good points on both, although I don't necessarily see a big contribution from lung control for changing trim while a surface float, per se.

I can shift about eight lbs without even thinking about it, about 15 lbs with some discomfort ... trust me, that will change your center of buoyancy.

Well, two things on this tangent:

First, in the context of a vertically-oriented "surface float" context, I do agree that one's lungs do make a difference in shifting the CP (lift) further forward (ventral), just like a drysuit air bubble will.

However, breathing is transient, so its contributions will also be transient. The kinematics are ... inhale = rock back & rise ... exhale = rock forward & sink. Since that second half resembles a "face dunk", we need to be careful that this mechanism is actually being beneficial to a surface floating diver.


Second, the magnitude of buoyancy change from breath control is quite dependent upon body size. The average (anthropometric 50th percentile) adult male has a lung Inspiratory Capacity of ~4 liters (8lbs); adult female is ~2.5L (5lbs). To invoke a 15lb shift requires a ~7.5L change in lung volume and while there are individuals with 7-8 liters of lung capacity, they're 99th percentile types like Lance Armstrong and not something that the average guy can ever expect to achieve, since exercise doesn't grow physically bigger lungs (just better utilized ones). Of course, bigger guys also means bigger exposure suits and thus larger buoyancy changes that need to be overcome in the first place ...


-hh