Jacket BC or Wing BC

[danvolker]

Well that settles it then doesn't it !!!! Drag is NOT a function of velocity squared.

How nice for you that this is what you get out of what I wrote....Someone else may alternatively have gotten that there are a great many variables which are not being considered, which destroys the validity of the science, but not the attempted claims.

[BDSC]

I always thought "Drag" was the way a guy dressed when he wanted to get in touch with his feminine side.

[danvolker]

The idea HH put out about towing the divers and measuring the resistance of each bc and configuration, is his best contribution to date on this.
It still misses actual trim involved in underwater propulsion, and effects on the propulsion of the diver, in how the BC fits them( whether it restricts optimal body mechanics or not, for optimal propulsion)...and it misses the mark on issues like how turbulence effects drag--as the turbulence issues will be very different in the boat towing, than the swimming....AND...this model will in no way address how fast a fit diver can swim with a slick BC system, versus with one that is not slick....or , how little this difference will be for a very non-fit diver, that does not swim fast enough to ever reach the critical speed required to have drag increase exponentially.

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As to the comments by DD and HH on my reactions to the "science claims"..... I have a strong science background myself.....enough to see how often journal articles begin with what they want to prove, then show nothing in the way of real proof on how they arrive at their conclusions, and then read the bogus conclusions..in fact, this is the norm for science journals...and the corporate funding of today's science makes this all the more appalling. Science has become the way you tell a lie, and then prove it as absolute truth to a gullible public. Fortunately there is good science going on also, but it is no longer possible to listen to someone because they say they are "using science"...this has almost become a "red flag".

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They're still anecdotes ... you have no scientifically objective data with which to argue against basic physics.

And yes, I do agree that technique is a contributing variable through elements such as kick efficiency - - but the scientific process examines only one variable at a time. The only variable under discussion here is the BC.



Yes, there's variation based on fitness. For example, a Tour de France elite athlete can sustain ~300 watts for an hour, but a power lifters can output up to 1800 watts ...but only for a few seconds. An average person will typically only be able to output ~125W over an hour ... which means the elite athlete is roughly only ~2x better.




Incorrect: I'm recognizing that elite athletes aren't representative of the 50th percentile human. They represent the 1% extreme.

Besides, haven't you noticed the obesity epidemic in the USA, Dan? If fitness were such a huge contributor, then shouldn't PADI be flunking more students?



What's easier still is to drag each diver behind a boat ... it eliminates the variable of diver fitness and does a better job of testing just the dive gear. Of course, Lee Bell offered to do this ... ten years ago ... and the salesmen making the "Our Gear is Best" claims ran away.




Hint: PAID OW, AOW, Rescue, DM, AI & Instructor standards don't require elite athlete performance minimums.




For mere seconds, such as a Power lifter.




Unfortunately, scientific papers that have measured the performance elite cyclist athletes have hard data that says otherwise. Here's but one example. And here's another. The measured science says that the difference is nominally only 2:1.

Now if we apply that 2:1 ratio to diver swimming velocities, for the same technique, fin, BC, etc, etc, etc ... the elite with 2x the available power is only going to be able to be SQRT(2) faster: +41%. That means 1.41 knots if the average diver is only able to do 1 knot max.

Immutable Physics. That's what you're trying to argue against Dan, not me.



-hh

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The smoke screen exists because from a marketing standpoint, divers - - especially new ones - - believe the hype.

That's how we've had fads before for many other dive widgets before this: brightly colored wetsuits, changes in training course names, fins with special vents, wetsuits with special linings, Force Fins, Split Fins, plastic balls that you release into the water that ascend at exactly 60ft/min, BCs that have depth-sensitive auto-inflation devices on them, self-deploying SMBs, Spare Air, ... the list of new, supposedly "better" equipment for divers to buy goes on and on and on.



-hh

As to your cycling stats, this is also a contentious area.....see http://americanroadcycling.org/artic...WattsSpeed.htm

Also know that a fit 210 pound cycling time trialer that is also good at the Kilo ( one kilometer time trial), can easily hit 600 to 1000 watts for a good burst---a burst equivalent to getting to a anchor line, or getting to a diver in great trouble....Body weight is not necessarily a liability underwater if the body is fit with very high VO2 max....it actually allows for much more power production, and the increase in surface area going along with an increase from a 160 pound person to a 210 pound person is negligable.

If the mathaletes in the cycling world, can argue ad nauseum about their issues, then your idea of "simplifying" by calculations is put in a better perspective....I propose the actual divers and bc's need to be tested, in all the effective categories.....when all the results are in, this will be more meaningful. You could attempt to caption the results with calculations that describe this, but there would be little reason to, since we would already have the answers.

[Teamcasa]

We live in an age where science it mis-used far more than it is used properly. ...

Science is often a tool wielded with little regard for truth, and with great regard for personal agendas.

Enjoy your science, and those who will listen to you. I will take my personal experiences over your formulas any day.

BTW, It's Physics and as I've said before, the plural of anecdotal is not data.

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Dan, if drag and propulsion efficiency are the key factors in what BC to choose, then why do they frog kick* (in a non silt dive), arms crossed across the chest, and knees bent up as opposed to straight legs and arms either out front of down their sides? Why carry all that extra gear in their drysuit pockets? Why take a can light? All of that stuff has real value but it adds more to the drag.

My view, drag is just one very, very minor factor in choosing to use a BP/W. The two major factors are one, the ability to use double tanks and second, it has a crotch strap. Everything else falls into the small benefit category. Plus, most divers that have a BP/W simply don't need another BC in order to dive, even nice warm water reefs.

The issue here is that a small number of people push the BP/W as the end-all-be-all of diving gear. While I agree that it's indeed a very good system, one that I use as well, but for a significant majority of divers, it's just not needed and not all that important in order to safely enjoy a dive.



*This is rhetorical.

[spc751]

In all those trips, I have never seen a single DM or Instructor wearing a BP/W. Not once. And I have made it a point to look since joining SB because of all the wild claims made on these threads.

The Instructor that did my AOW this winter was wearing a BP/W.

[danvolker]

BTW, It's Physics and as I've said before, the plural of anecdotal is not data.

Another saying....."Good Science is Good Observation".


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Dan, if drag and propulsion efficiency are the key factors in what BC to choose, then why do they frog kick* (in a non silt dive), arms crossed across the chest, and knees bent up as opposed to straight legs and arms either out front of down their sides?

Propulsive efficiency is achieved with perfectly trimmed out diver in bp/wing, and frog kick is often utilized because it allows absolute minimum heart rate--the frog kick with big long glide is very efficient, the way our biomechanics work for a good push contraction and a big rest.....ultra low heart rates will mean less air consumption and potentially longer bottom times, or less in-gassing than high heart rates at same duration. If the arms are in the correct plane in front of the diver's head, they help with lowering turbulence and adding stabilizing wing effect , this can lower drag of the frontal area of the diver, and it also allows guages and compass to be read instantly.

Personally, I have felt very slick with my arms at me side going at extreme speeds, and have not noticed a large advantage in having the perfect arm cross in front of me....there is perhaps some. For me, with a video camera, this aspect is not typically relevant...the camera is in front of me in the GUE position :-)

There is only a small amount of gear I would carry, a spool for instance, and I tuck the smb in the storage pouch behind my back. Thigh pockets are relatively low drag---chest or stomach pockets are IN a high drag area, and you can feel them "pulling" in a high current. My can light is low drag where it is, and is awesome for buddy communication. Also I route my 7 foot hose under it....and in my case, the cannister light battery runs my video lights--which are crucial to decent video :-)

[Teamcasa]

...Propulsive efficiency is achieved ...<snip>... the way our biomechanics work for a good push contraction and a big rest...

Any good kick can follow these same rules. Propulsion does not care if the fins are going up and down or back and forth - only the diver following you cares.

... For me, with a video camera, this aspect is not typically relevant...the camera is in front of me in the GUE position :-)

Is that one handle in each hand?

There is only a small amount of gear I would carry, a spool for instance, and I tuck the smb in the storage pouch behind my back. Thigh pockets are relatively low drag---chest or stomach pockets are IN a high drag area, and you can feel them "pulling" in a high current. My can light is low drag where it is, and is awesome for buddy communication. Also I route my 7 foot hose under it....and in my case, the cannister light battery runs my video lights--which are crucial to decent video :-)

It's all drag. And that's my point, a properly trimmed, efficient diver will be happy using most any system if it's squared away.

[MMM]

Moderator's Comments:

While this was an old thread that was resurrected, it appears that time has not dulled the debate as people are clearly still very passionate about their choices. Please remember to keep discussion friendly and constructive regardless of your stance on the issue.

[danvolker]

Any good kick can follow these same rules. Propulsion does not care if the fins are going up and down or back and forth - only the diver following you cares.

You know, you'd think that, but I do think the frog kick shape I use for this is actually like a "gear change" on a bike, where the fin surface is very stiff in this angle of motion, and pushes a great deal of water.....and then the long glide allows the heart rate to remain very low....If I try one Flutter, it is too small a gear in this kick shape, to push enough for a singe flutter up/down to do enough for a big glide. Flutter is more of a higher kick turnover style kick, that puts more oscillation into the fin, than frog kick....Higher kick turnover is going to cause Heart rate to rise...the trade off is it will work the muscles harder...So you use the largest "gear" you can, to keep the Heart Rate as low as possible( low HR is low breathing rate too), but not trash your leg muscles to the point of fatigue or cramping ( cycling training is awesome for this)
A dolphin kick can almost do the bigger water push of the frog--from it's motion dynamics and angle, , but is less comfortable for very long duration, at least for me....I prefer to use dolphin kick for very high speed issues, sometimes a hybrid between frog kick and dolphon kick, which can be used slower, and with more comfortable long duration.

Is that one handle in each hand?

Yes...Canon 5 D mark II in an Aquatica housing with two Cave Video lights..run by my cannister.

It's all drag. And that's my point, a properly trimmed, efficient diver will be happy using most any system if it's squared away.

I agree....I used to love diving just with a harness and steel 72, with no BC at all. With Lycra, I needed no BC for weight changes, and tank flotation near dive end was never an issue of concern.
I have never carried ANYTHING with me that I did not have to. Now with a big honking camera, I do have some drag issues, but I keep everything else slick, so the camera ends up not hurting my efficiency much compared to how most divers are set up....

[-hh]

BTW, It's Physics and as I've said before, the plural of anecdotal is not data.

There have been opportunities presented on a Silver Platter to go measure data ... and one would particularly expect that if a manufacturer really did have a better product that they would welcome the opportunity to crush his competitors with hard data.

But no, it doesn't happen. It has been observed that such opportunities have fallen through so many times that it can hardly be considered a mere coincidence anymore...although scientifically, any purposeful intent to deceive hasn't been proven.

In layman's terms, the remaining manure is simply too deep to believe the claim that the stable is clean.

Dan, if drag and propulsion efficiency are the key factors in what BC to choose, then why do they frog kick* (in a non silt dive), arms crossed across the chest, and knees bent up as opposed to straight legs and arms either out front of down their sides? Why carry all that extra gear in their drysuit pockets? Why take a can light? All of that stuff has real value but it adds more to the drag.

And hey, let's throw in the "long hose" as another source of drag too. Afterall, if drag streamlining is the most important factor in one's dive gear setup, then the long hose must come under fire.

My view, drag is just one very, very minor factor in choosing to use a BP/W. The two major factors are one, the ability to use double tanks and second, it has a crotch strap. Everything else falls into the small benefit category.

Which is really where observation as how it contributes to the scientific process takes us on our journey to identify significant contributing variables to quantize. The human plays the biggest part, through their control over the variables of trim, weighting, fin choice, fin stroke mechanics, "cotton arrangement", their personal fitness levels, dive planning (intelligence over braun), etc ... and for the diver as a consumer*, it should be noted that these contributing variables are mostly "Free" in that they don't come from a $500 widget from a manufacturer's catalog, but simply are personal skills development.

* - especially for the Novice diver seeking good advice, since this thread was originally in SB's "New Diver" section

Plus, most divers that have a BP/W simply don't need another BC in order to dive, even nice warm water reefs.

The biggest hazard of diving in warmwater with a larger-lift BC isn't in the water, but at the airport, in the form of an airline overweight baggage fee. And a BP/W user with a weighted STA isn't going to be treated any differently by the airline.

The issue here is that a small number of people push the BP/W as the end-all-be-all of diving gear. While I agree that it's indeed a very good system, one that I use as well, but for a significant majority of divers, it's just not needed and not all that important in order to safely enjoy a dive.

Well said. Unfortunately, the more that the BP/W is promoted as the "best solution for everything", the more that it will develop a reputation as being snake oil that isn't good for anything.


-hh