Are you all just technical? What is technical?

[acteg]

What is this crotch strap you speak of? Never knew It was an even an option on the traditional BCs. I have a crotch strap for my BP/W but never use it. Don't see a need so far. Everything stays firmly in place (right side up, upside down, etc).

The effect of feeling that your tank is fused to your back arises from a combination of having the rig properly adjusted, having a crotch strap, and having the correct posture in the water. Properly adjusted shoulder straps are not tight - you should be able to slip in and out of them, even with a bulky suit. The BC is pulled tight onto your shoulders by the crotch strap when you tighten it, "fusing" the system to your back. The tightness of the fit is increased (but not uncomfortably so) when you extend your arms in front of your body in a Superman-like pose as this shifts your muscles (predominately your deltoid and trapezius), effectively elongating your torso. This kind of fit can be achieved by any buoyancy compensation device fitted with a crotch strap. Some properly-adjusted single-tank BCDs can have a "sloppy" feel if there is no anti-roll mechanism (either a single-tank adapter, STA, or a modified wing with "nubs" to prevent/minimize tank movement) which keeps the tank from swaying about.

 

[DevonDiver]

That's 50 minutes of harness adjusting for 10 students, compared to about 2.5 minutes of students slipping into a conventional, easily-adjustable jacket or back-inflate.

That's a short-term 'instructor convenience' approach, that disregards the points I made earlier about enabling more intuitive grasp of stability, trim and control in the water.

Are we talking about "minimizing an OW course to it's barest essentials in the shortest possible time (for the instructor's benefit)", or are we talking about what is best for the student as a developing diver?

a. They're a lot more comfortable than Horsecollars, which is what they replaced;

Many would say that BP&W were a lot more comfortable than Jackets, which they are replacing...

b. They permit a (higher and) more comfortable float position;

Except that they often allow the diver to 'sink' inside the BCD, supported by their armpits, flailing on the surface with their arms jammed upwards..and chin barely above the water line..

Crotch strap helps that immensely. Many jacket BCDs have crotch straps nowadays....?

c. They continue to have easy/quick adjustment points;

If a BP/W has a tailored fit, it doesn't need adjustment points.

That said, a BP/W can be fitted with a 'comfort harness' with all the same quick-adjustment (and more) that a jacket BCD has.
Can a jacket BCD easily be reconfigured to give a custom fit? Vice-versa??

To be honest, it's like arguing that a cheap 'off-the-shelf' suit is better than a tailored bespoke suit...because the cheap suit has braces to hold the trousers up...

The net sum of the above is that its the fast path to a setup that a novice will feel comfortable with.

I see no intrinsic link between the words "fast" and comfortable".

As stated, my experience has been that many, many entry-level students are particularly 'uncomfortable' in a jacket BCD... assuming, that is, we are talking about in-water comfort... and not the convenience of the changing room...

...unfortunately, the small(?) percentage that have tried a wing but found them unsuitable for their needs and have said so, tend to be vigorously criticized by others, frequently with suggestions that they’re guilty of "doing something wrong" and/or are incompetant. The reality is that something probably is different, but the logical fallacy is that different doesn’t automatically equate to being wrong.

I don't think that anyone claimed that BP/W was universally perfect. However, the positive testaments of those switching to BP/W grossly...vastly outnumber the very infrequent negative ones from divers switching from a BP/W.

I have seen divers struggle to acclimatize to BP/W diving - mainly due to a lack of, or poor, initial instruction and/or a lack of effective research on the configuration... and the specific issues that need to be addressed when diving it. It's different - it requires some though... effective equipment specific training helps (of course), but isn't essential... because we have the internet... and most people have sufficient brainpower to problem solve their way into efficient BP/W use..

Some divers have spent many decades in a jacket BCD... and the familiarity they have with that configuration will outweigh the benefits of moving to a BP/W. Some divers just don't like change... Neither of those points are relevant to a novice diver.

Very well said, and I find this attitude (that everyone must become a jet fighter pilot) to be disconcerting and quite disappointing, because it carries an assumption behind it that ‘most’ divers eventually go in a particular direction ... with zero substantiating statistics to support their assumption. ​

I think the whole point of this thread was to question whether BP/W was 'technical'. The resounding answer is 'no. It is a migration of technology/configuration from the technical community (a 'best practice'), but there is nothing remotely 'technical' about a single-tank wing on a backplate.

Every BCD...jacket or otherwise... has some form of a backplate..a harness..a buoyancy cell and LPI. Using those functions, regardless of where the buoyancy cell is mounted, what material the backplate is made from, or how may plastic clips are on the harness...does not constitute a technical diving skillset. The skills required are the same...are identical...to those taught to any OW diver...

....and there are statistics about diver progression to technical diving... I'm sure most agencies can supply them.

It's a booming activity... evidenced by a rapidly expanding technical diving curriculum, flourishing numbers of technical diving instructors/centers... and the increasing trend towards 'tecreational' training such as 'rec sidemount' and 'rec CCR'.

​

...

there’s better than 50% odds that five years from now, their gear decisions are irrelevant, because they’ve dropped out of the sport. Whatever gear they bought will be sitting in the bottom of a closet, waiting for a garage sale to get rid of. ​

When someone asks for advice, I don't give it on the basis that "they'll probably drop out". Perhaps the giving of advice with that attitude represents a factor in why some divers lose interest...?



​

 

[Them]

There are too many awesome posts to single out any one, but I want to repeat my thanks to everyone for their great contributions. I also want to thank the folks who have offered to show me the ropes with some of this gear in person. A truly amazing bunch of people hanging out around here.

...
Not quite – you got the moment arm’s directions transposed:

A full tank would be negative and using the first illustration, result in a clockwise (‘face up&#8217 torque. But make it now an empty tank (end of dive) and instead of it pushing down, it is floating up, so it will become a counter-clockwise (‘faceplant&#8217 torque.

Huh. I just don't see that model.

To maintain the same buoyancy with a full and empty tank, you must change the displacement by somewhere around 160 cubic inches. I'm just doing that in my head so I may be off by a bit. So if you have a full tank + 160ci of displacement you will have the same buoyancy as an empty tank + 0ci of displacement. If the variable-displacement buoyancy is short arm (e.g. if there was a piston in the cylinder itself) then controlling the buoyancy will not cause pitching.

If, on the other hand, the variable displacement buoyancy is on a long arm, then as the tank gains buoyancy (and therefore the variable displacement buoyancy loses buoyancy to maintain the same overall buoyancy) the tank will ride higher and the variable displacement buoyancy will ride lower. The longer the arm, the greater the moment for a given buoyancy difference. If the variable displacement buoyancy is in front of the diver, that will cause a forward pitch.

The forward pitch can be offset by increasing the displacement of the variable displacement buoyancy to beyond what is needed to maintain constant buoyancy. It seems as though that would leave you floating high on the surface. That may or may not be desirable - I don't know enough to really judge but my instinct is "not".

Anyway, it's easy to get turned around depending on which direction you start from.

I see the "try before you buy" argument. Gotta say I'm really tempted by this combo, more or less:
AL back plate w/ Oxycheq Hog Harness & Oxycheq Mach V wing [DROCpkg] - $375.00 : Cave Adventurers!, We will NOT be undersold!!! (w/ ss bp $400 total)
HOG Single Tank Regulator Package [HOGsingleregpkg] - $449.95 : Cave Adventurers!, We will NOT be undersold!!!

 

[nimoh]

DevonDiver,

when you asked "

Why exactly are jacket BCDs "better" for beginners? I never quite worked that out..​

", did you already have your next post ready to go?

 

[rhwestfall]

I still think the BP/W was the result of a guy being drunk when he suited up and put his gear (horse collar) on wrong (or should I say "right"??????)..........

 

[Crush]

To maintain the same buoyancy with a full and empty tank, you must change the displacement by somewhere around 160 cubic inches. I'm just doing that in my head so I may be off by a bit. So if you have a full tank + 160ci of displacement you will have the same buoyancy as an empty tank + 0ci of displacement. If the variable-displacement buoyancy is short arm (e.g. if there was a piston in the cylinder itself) then controlling the buoyancy will not cause pitching.

This may be an incomplete answer, but: underwater your empty AL80 may be buoyant. However, recall that at the surface your tank will be partly out of the water, decreasing its buoyancy.

 

[Them]

This may be an incomplete answer, but: underwater your empty AL80 may be buoyant. However, recall that at the surface your tank will be partly out of the water, decreasing its buoyancy.

True, and the dynamics of a fairly massive object displacing a variable amount of water/providing a variable amount of unsupported weight above the surface behind you, plus a rather low mass bladder in front of you, would be complicated in any sort of real-world situation.

Always funny how the simple diagrams really don't capture the reality of a dynamic system all that well.

 

[GrandpaScuba]

...He then showed me some Zeagle BCs that he thought were "A better starting point." Since one of my concerns was packability he demonstrated how it could fold up for travel. The Zeagle actually did look quite nice to my noob eyes.

So, was he right? Are y'all technical? If so, how does that relate to the folks recommending HOG regulators and the like? Is it all just "Pick your Koolaide"?

He's sort-of right. Tech divers tend to come from the ranks of the more experienced divers. And the "more experienced divers" are also the type that like to spend all day online telling everyone how experienced they are.

There are a lot of people who really aren't "tech divers" using "tech" equipment. You dive shop guy is right. Tech gear is more customizable. So, the "tech craze" has been a real boon to those of us who are Big and Tall divers. Most of the mainstream dive equipment manufacturers are like clothing manufacturers, and only supply their equipment in a narrow range of sizes. Tech and tech-like equipment allows those of us who don't fit properly into mainstream gear the ability to build a rig that is just-right for us.

That said, his recommendation of Zeagle is good. Zeagle makes a point of making their gear highly customizable. Rather than going the tech route, I use Zeagle gear, myself.

Also, tech gear appeals to the do-it-yourself'ers. And outdoor people tend to be DIY'ers.

And then, finally, after you get 1000 dives under your belt as a recreational diver, many divers are looking for a bigger challenge, and tech diving may give them what they are looking for.

Me? Well I'm one of those "over 1000 dives" divers, but I still just like to sit on the bottom and look at all the pretty fish. I've done deep diving, current diving, wreck diving, and so on. But really, 90% of what there is to look at underwater is between 30 and 60 feet.

 

[spectrum]

The instructor I saw using BP&W was doing a family group quite easily just by having shoulder strap adjusters as part of his rigs. Nobody say's it needs or wants to be a hardcore one piece harness, I use sliders to go effortlessly between suits.

 

[-hh]

There are too many awesome posts to single out any one...

(Force analysis)

Huh. I just don't see that model.

To maintain the same buoyancy with a full and empty tank, you must change the displacement by somewhere around 160 cubic inches. I'm just doing that in my head so I may be off by a bit. So if you have a full tank + 160ci of displacement you will have the same buoyancy as an empty tank + 0ci of displacement. If the variable-displacement buoyancy is short arm (e.g. if there was a piston in the cylinder itself) then controlling the buoyancy will not cause pitching.

If, on the other hand, the variable displacement buoyancy is on a long arm, then as the tank gains buoyancy (and therefore the variable displacement buoyancy loses buoyancy to maintain the same overall buoyancy) the tank will ride higher and the variable displacement buoyancy will ride lower. The longer the arm, the greater the moment for a given buoyancy difference...

Right, and what we have are two (at least) sources of variable buoyancy: the tank and the BC.

Assuming a mounting location behind the diver (not sidemounts), we know that the tank is going to have a moment arm.

The BC's moment arm ... will depend on just where the air bag is located.

What we've not identified is where we're measuring to ... the mass centroid of the diver-as-a-system is probably right about at the spine at belt height.

Going with that, we can expect that the centerline of the tank will be probably ~6" behind the diver's spine.

Next, looking at the different BC types and generalizing where their effective centers of lift are for each configuration, let's assume a horsecollar 1" in front of the diver, which would put it ~10" forward of the spine. A Wing is going to be behind the plate/backpack and approaching the centerline of the tank...call it 1" offset plus a quarter diameter, for 3" total. The Jacket can vary a lot but if we center it on the thoraxic centerline, we're looking at 4.5" forward before any consideration for how they would be biased rearwards by the commonly seen bladder configurations...call it a swag of 2" forward? In any case, the obvious trend is that a horsecollar is furthest forward, then a Jacket and then a Wing furthest towards the rear (towards the tank).

If we're now looking at a (beginning of a dive) full tank that's negatively buoyant, it is pulling down (side view - 'clockwise' torque), plus each BC will need extra air (volume) to maintain the same float: the moment arm's length won't change, but the force at the end of it will increase, which increases the torque. For this setting, both the Horsecollar and Jacket can be assumed to be forward of the mass centroid and thus be also creating a clockwise torque ... makes the total effect greater in magnitude (face up torque). The Wing is on the tank's side of the centroid, so it is actually in the desired location to counteract the negative tank...but we'll have to keep this in mind when we go to the empty tank.

At the end of the dive, the tank is now less buoyant, and for some common AL tank configurations (ie, resort AL80), it has now flipped from a clockwise torque from a negative tank to a counter-clockwise torque from a positive tank...moment arm length remains the same. For the BCs, there's less lift required for the same magnitude of float and now the horsecollar & jacket are in the right place to counter the tank's torque...and the wing is not: it is additive, and being clockwise from both the tank & BC, this is where the 'face down' element can come into play.

If the variable displacement buoyancy is in front of the diver, that will cause a forward pitch.

I was with you until this statement. I think what you're trying to say is that with an empty tank, the 'variable displacement' required from a BC becomes less (yes), so if the BC is locaded forward of the diver, this reduction in buoyancy being provided will result in a forward pitch. If so, then I agree...but I'll also point out that for that scenario and for an end-of-dive surface float use case, there's not much of a downside to simply adding more air and floating higher out of the water. Yes, one will hear "Jacket Squeeze" get mentioned and this is a problem on some really old (1980s) and cheap designs, but this isn't a universally foregone conclusion: a good jacket design does not have this problem.


-hh