Sidemount BC

[Razorista]

... and, as such, it is not a "very old known fact". Indeed, it is made-up gibberish and nonsense, regurgitated by people who haven't bothered to check the reality and/or have no direct personal experience of the issues involved.

It's also personal experience @DevonDiver.
Caught enought people with failed overpressure valves and even more often had divers shouting upward because of an overreaction caused by fear after a previous experience.

It would not even matter if that fear was caused by facts or internet rumors.

 

[decompression]

The problem with those wings is not the overall size.
The are either bungeed into shape or constructed with other constriction methods.

Constricting the wing, however, will increase the pressure on the dump valve with a full wing.
Trying to carry a heavy load with a full wing especially at depth can cause the dump-valve to overreact and dump overpressure early, severely reducing the maximum wing capacity.
You loose at least the last 2-3 liters / 4-6 lbs that way, if you want to be sure with a small margin of error on top.

Why would the wing be full?

 

[Razorista]

Why would the wing be full?

That, on the other hand, is a very valid question with those over-sized monstrosities most prefer.

 

[DevonDiver]

It's also personal experience ...
Caught enought people with failed overpressure valves and even more often had divers shouting upward because of an overreaction caused by fear after a previous experience.

The issue was whether bungeed wings decrease maximum buoyancy potential. You have dodged the rebuff of that claim.

Whether or not some diver inappropriately over-react to their OPV releasing gas in inconsequential. That merely indicates a failure in their most basic diving education.

When an OPV releases gas upon full inflation of the wing it is working implicitly as designed. It is not a "failure". The clue is in the name... "Over-Pressure Valve".

 

[Razorista]

I tried to explain that the wings can disappoint expectations in moments where you rely on them.
Mostly thís requires mistakes in construction, misjudging bungee strength, etc...

If you take into account that there have been reports and warnings about wings disappointing that way, you have to assume this wing also might not deliver it's full theoretical capacity.

In practice?... well I dove with people with wings of nominal capacity far exceeding my own who could not even hold themselves at the surface with a normal set of tanks.
I meet lots of people with very small sidemount wings, that failed them just after they started to think they worked everywhere.

The bungees can have significant effect, wouldn't you agree? .
In particular the Hollis SMS100 wing works better with carefully applied bungee, because that reduces air trapping at the top.

I would not know how to 'prove' that the wing capacity is reduced, I would not know a way to conclusively prove it doesn't either.
So in my opinion, when you calculate your dive, you have to assume it does reduce capacity.

 

[tbone1004]

That, on the other hand, is a very valid question with those over-sized monstrosities most prefer.

says the one diving a 45lb wing... Which is the same size as most of the "oversized monstrosities" he mentioned...

 

[Razorista]

says the one diving a 45lb wing... Which is the same size as most of the "oversized monstrosities" he mentioned...

My only qualm about the Razor 2.1 - much do big for me.
But at least it stays streamlined if only used to a quarter capacity very well.

 

[jnowak100]

If you only do one type of diving in one location, buy the best for that. If you do different types of diving in different locations, and cant afford or dont want multiple rigs then you choose optimal instead of best, sacrificing "best" to gain optimal versatility. I have a Dive Rite Nomad XT, I dive single, doubles and sidemount everything from a single aluminum tank to 2 steel 15ltr with 2 aluminum 11ltr deco tanks, drysuit to boardshorts. I have taught OW and Tec in the same weekend, the reconfiguration is easy, and I avoid multiple sets of gear. There is no "best" only what works best for you.

 

[DevonDiver]

I tried to explain that the wings can disappoint expectations in moments where you rely on them. Mostly thís requires mistakes in construction, misjudging bungee strength, etc...

I would not know how to 'prove' that the wing capacity is reduced, I would not know a way to conclusively prove it doesn't either. So in my opinion, when you calculate your dive, you have to assume it does reduce capacity.

Different bungee has varied tensile strength and also a limit of extension. The tensile strength only needs to be sufficient to draw in slack material when un-inflated. The limit of extension must meet, or exceed, the size of the fully inflated wing.

As mentioned, I have significant real-world experience diving bungeed wings, backmount and sidemount, and have never experienced a problem with manufacturers getting the bungee selection wrong. I've never seen a bungeed wing that suffered from reduced capacity because of a manufacturer oversight on the (above) factors.

Even your beloved Razor uses bungee which can influence wing volume. That's what happens when you bungee around the torso. But the bungee does not limit the max buoyancy when you need it. The bungee would get tight around the stomach if the wing was fully inflated, but the wing would inflate. Correct?. The OPV wouldn't burp until max wing capacity was reached.

I modify SMS100 for students sometimes (see pic below). That involves significant shortening of the supplied bungee. It's appropriate for diving in my location; tropical, warm-water. Without the modification, there is certainly no impact from the bungee on wing capacity. When I teach the modification, I demonstrate that the wing can be 'shaped' by slightly tightening the bungee around the wing. This, however, still preserves sufficient flexibility in the bungee to permit full inflation of the wing (as supplied, the bungees are very loose).

I then demonstrate how the wing capacity can be reduced by tightening the bungee much further, so that the bungee reaches it's maximum stretch before full wing inflation is achieved. Reducing wing capacity is the goal, and you have to more than double the stretch/pre-tension on the bungee, (relative to how it was rigged 'out of the box') to make that capacity reduction.

 

[cool_hardware52]

The problem with those wings is not the overall size.
The are either bungeed into shape or constructed with other constriction methods.

Constricting the wing, however, will increase the pressure on the dump valve with a full wing.
Trying to carry a heavy load with a full wing especially at depth can cause the dump-valve to overreact and dump overpressure early, severely reducing the maximum wing capacity.
You loose at least the last 2-3 liters / 4-6 lbs that way, if you want to be sure with a small margin of error on top.

The cracking pressure of an OPV is a function of the spring used, the amount of preload and the area of the poppet. You could put "C" clamps on 1/2 the wing and it would not change the cracking pressure of the OPV…..


Tobin