Vote on your preferred BC -

[ICY ICE]

In essence, what you are measuring are the opinions of frequent scubaboard members who are interested in this topic, and on that count your findings are very clear!

I disagree; the randomness of the current members polling is equivalent to sending an anonymous poll to active/non active members. I accidentally found this thread and submitted my poll, as everyone else has done, how is that not random?

 

[meisburger]

Its not random because you saw the title of the thread and then clicked on it, indicating you have an interest in the subject. Of the hundreds of people who scanned the new posts and read the title, just a small percentage clicked to take the poll. Many others went on to learn about the latest singles trip to Cozamel, or to debate the merits of digital vs film, or to compare the length of their snorkels. I do surveys as part of my job, and understand sample bias.

What we can reasonably say is that the findings are reflective of that group of scubaboard members who have an inordinate (unhealthy) interest in the BC - BP/W debate, or who are naturally argumentative.... I wonder which I belong to?

The Other Tim

 

[JeffG]

What we can reasonably say is that the findings are reflective of that group of scubaboard members who have an inordinate (unhealthy) interest in the BC - BP/W debate, or who are naturally argumentative

Thats a stretch

 

[Mike Veitch]

oops

 

[Mike Veitch]

Thats a stretch

Shouldn't you call yourself Bert?

Just a random sampler...

 

[Shiprekd]

I'll just keep on diving solo, buddy and DM with my jacket BC's for another 3 thousand dives. I'm comfortable because I have my system rigged the way I want. I like the fact I don't have to "attach" and adjust pockets. I surface more times than not with pockets full of trash, or stick someone's ill fitting leg knife in my zipper pocket. Write on my slate a multitude of times, watch some "free willy" bp/w with a crotch strap, booties & bermudas trying to adjust his multitude of mini weights for perfect trim.

While jacket flogging seems acceptable, I'll be more than happy to extend my 2 cents that it takes a world more skillz to master a decked out jacket rig. If you can dish it out, then you better be big enough to take it without making excuses. Don't bet on the manufacturers, LDS's, and dive ops converting exclusively to bp/w anytime soon. It's a niche.... for now. BTW - what happened to the "in" VW beetle a few years back?????? Seems it is back where it started.....

Personally, I'm not so self-righteous to preach one kind of system (this vs that) to ANYONE. As a DM, I'm constantly asked what I would suggest. My reply??? Go with the style you were trained in and let YOUR comfort and PROFICIENCY decide what you want or want to venture into.

Forgive my forward nature to those of you whom are sincere in showing people "other" choices w/o preaching or dissing what people want and can afford....

 

[MXGratefulDiver]

Personally, I'm not so self-righteous to preach one kind of system (this vs that) to ANYONE. As a DM, I'm constantly asked what I would suggest. My reply??? Go with the style you were trained in and let YOUR comfort and PROFICIENCY decide what you want or want to venture into.

I agree ... as a BP/W user and scuba instructor, when anyone asks me what style BCD is best for them I reply "the one that FITS".

A pity that two or three people in this thread keep insisting that all BP/W wearers must be fashion-conscious dive nazis ... because that's not what I see in real life at all. But I think it's pretty obvious by the replies who's got attitude issues.

... Bob (Grateful Diver)

 

[-hh]

Given every item of equipment and the posibility of placing i am sure we could make anyone in any type of BC (wing, BI or jacket) fall on their face the key is to balance it - which really isnt that hard even with an AL80 near empty.

True, it can be done. The question is just if the solution remains fairly conventional, or if we need to reach into our bag of tricks for some "non-standard" items to solve it, and if there's a particular BC design that needs that little bit of extra help more often than the alternatives.


Consider the following:

An empty AL80 is +2 lbs, and because of its 4" radius, will have its center of buoyancy around 4"-6" behind the diver's back. Call it 5" behind the back for easy math.

A Nikonos V with dual SS-200 strobes is around -2lbs, and will generically have its center of mass in front of the diver's chest. Call it 5" in front (again for easy math).

Anthropometrically, 5th/50th/95th percentile values for the Thorax (Chest) of an adult American male are 8.25", 9.50", and 11.04". A nice round value in the middle is 10". We need to know this because the above values are measured from chest and back (not middle).

Assuming that the diver's center of mass is in the middle of his body, then we get the following torque values that this diver is exposed to...when his body is vertically oriented:

AL80: (5"+10"/2)(+2lbs) = +20 inch-lbs
N-V: (-5"-10"/2")(-2lbs) = +20 inch-lbs

FYI, I'm using textbook "right hand rule" for my coordinate reference system, but any one that you could use will reveal that these torques are additive: the net effect is +40 inch-lbs torque.

Note that we've not included the BC yet, but this diver has undoubtedly been torqued "face down".

You can either use science and mechanics to solve or create (also a misapplication of science) problems.

...continuing to apply no-BS science to examine the problem, to look for solutions:

First, let's assume that the BC is providing +8lbs of lift and the diver's still vertical, such as he would be at the surface, where its generally desirable to not be face-down.

If the BC design is a horsecollar, then its buoyancy is right on diver's chest:
HC: (-5") (+8lbs) = -40 inch-lbs
--> Net torque: +40 inch-lbs - 40 inch-lbs = 0 inch-lbs ...diver now has zero rotation.

If the BC design is a jacket, then the net buoyancy is centered on diver's center:
JKT: (-0")(+8lbs) = 0 inch-lbs
--> Net torque: +40 inch-lbs - 0 inch-lbs = +40 inch-lbs ...diver rotated face down


If the BC design is a Back Inflation, the buoyancy is behind diver's back. Assume its the best low profile bladder anyone has ever seen, but is raised by 1" by the STA:
BPW: (1"+5")(+8lbs) = +48 inch-lbs
--> Net torque: +40 inch-lbs + 48 inch-lbs = 88 inch-lbs ...diver rotated face down worse!



One solution would be to eliminate the camera:

HC Net torque: +20 inch-lbs - 40 inch-lbs = -20 inch-lbs ...diver rotated face-up.
JKT Net torque: +20 inch-lbs - 0 inch-lbs = -20 inch-lbs ...diver rotated face-down
BPW Net torque: +20 inch-lbs + 48 inch-lbs = +68inch-lbs ...diver is still face-down.


The way that we normally counteract this torque is by finning. Since the fin's on its own moment arm...let's call it around 3ft...we can calculate the amount of effort (continuous kicking) it will take for the diver to counteract the torque and keep his face out of the water:

BC -- No camera -- With camera

HC none none
JKT ~1/2 lb ~1.1 lbs
BPW ~1.9 lbs ~2.5 lbs

YMMV on when this finning becomes noticable. Or fatiguing on longer surface floats.

Getting back into the Science, if we try to solve the problem instead by adjusting our gear, its pretty straightforward to calculate how much of our weightbelt's mass we would have to displace rearward. The Horsecollar doesn't have a problem, and the Jacket's pretty easy...the worst case is the BPW, because its needs to generate -88 inch-lbs of counteracting torque. This could be done by:

-20lbs @ 4.4" moment arm length (would put it nearly to the divers back...consider it to be approximately a weightbelt in the small of the diver's back). Of course, if you're warmwater diving, you don't have a 20lb weightbelt, so this solution won't be enough by itself.

-10lbs @ 8.8" moment arm length (puts it 3.8" behind the diver's back, such as a weighted backplate). Of course, if you're warmwater diving, this now means that this weight has to travel in your checked baggage (50lb/bag airline weight limit may apply).

-6lbs @ 15" moment arm length (puts it 10" behind the diver's back, which is roughly the far side of the AL80 tank): this is the "weight on the BC tank strap" solution.

So now the question (at least for me) is: "who wants to recommend a good quality BC tank strap weightholder that's also big enough to accomodate a 5lb or 6lb weight?" If no such product exists, then IMO there is no good solution.





-hh

 

[simbrooks]

Getting back into the Science, if we try to solve the problem instead by adjusting our gear, its pretty straightforward to calculate how much of our weightbelt's mass we would have to displace rearward. The Horsecollar doesn't have a problem, and the Jacket's pretty easy...the worst case is the BPW, because its needs to generate -88 inch-lbs of counteracting torque. This could be done by:

-20lbs @ 4.4" moment arm length (would put it nearly to the divers back...consider it to be approximately a weightbelt in the small of the diver's back). Of course, if you're warmwater diving, you don't have a 20lb weightbelt, so this solution won't be enough by itself.

-10lbs @ 8.8" moment arm length (puts it 3.8" behind the diver's back, such as a weighted backplate). Of course, if you're warmwater diving, this now means that this weight has to travel in your checked baggage (50lb/bag airline weight limit may apply).

-6lbs @ 15" moment arm length (puts it 10" behind the diver's back, which is roughly the far side of the AL80 tank): this is the "weight on the BC tank strap" solution.

So now the question (at least for me) is: "who wants to recommend a good quality BC tank strap weightholder that's also big enough to accomodate a 5lb or 6lb weight?" If no such product exists, then IMO there is no good solution.

Nicely presented, i like your methodology. So lets take me as an example with my typical 3mm wetsuit weighting - i need my SS BP (-6#) and about 6# of additional weight with the aforementioned config. So here we have -6#@6" (to my BP) and the other 6#@10" on my tank straps, total net = -96in-lb, i guess my rig is near balanced and i dont flop in head first, in fact i have a couple that is pointing me face upwards without need for finning. I have two tank weight pouches, each can hold up to 5# hard or 4# soft - i could put 4 or more of these on my straps if needed. I bought them from DRE for about $10 a piece

I still find floating on my back is much simpler and more relaxing

 

[RiverRat]

It's kinda neat to see the science breakout of what is really going on when one is floating on the surface. But I can honestly tell you this. I've dove both my 9# SS backplate with a 3# belt and my 2# AL backplate with a 10# belt and, although I prefer a lighter belt, I didn't notice much of a difference at the surface. Same wetsuit, same AL tank. Same with my steel tank, AL plate and a 4# belt. I am curious now, for my own interest, to do some side by side comparisons.