Sidemount BC

[Razorista]

I do not get the point you are trying to make @tbone1004

You compared apples and oranges and that lead you to the wrong conclusion, it looks like.

Bungeeing a backmount style wing for sidemount serves two main purposes:
1. Reducing the flapping around of the empty and partially filled wing.
2. Forcing the air on the partially filled wing to concentrate at the hips, instead of the shoulders.

When you fill a wing bungeed like that to full capacity the inflator or oral inflation has to overcome the force and when it is filled at last you will loose all effect the bungees had on the wing.
When your trim fails suddenly most normally compensate by filling the wing an bit more, since this wing is already full, most will acctualy drop a few meters in the progress I think.

Anyway: the bungee is meant to restrict the wing a bit, either it will, or it can be removed, since it does not help then.

Since you mentioned the Razor let my try to explain that part again:
When the Razor is bungeed too tightly the wing will not inflate to maximum capacity before the bungee cuts into you to much.
At the same time the weight pieces below the wing are pressed into it and reduce it's capacity before the overpressure valve starts to burp.
It is something one has to take into account when diving a sidemount system (most or probably all) with a large wing and lots of weight attached.

 

[cool_hardware52]

At the same time the weight pieces below the wing are pressed into it and reduce it's capacity before the overpressure valve starts to burp.

Lead is more than 11 times more dense than water. Even 25 lbs of lead under a Razor wing, assuming it fully displaced the available air, would only reduce the capacity of the wing by a little over 2 lbs ~ 1 kg. It's just not an issue.

Tobin

 

[Razorista]

Lead is more than 11 times more dense than water. Even 25 lbs of lead under a Razor wing, assuming it fully displaced the available air, would only reduce the capacity of the wing by a little over 2 lbs ~ 1 kg. It's just not an issue.

Tobin

Since the wing cannot 'unfold' with the bungee too tight the T-weight system is pressed into the wing, it's not the lead volume, it is pressed against the wing with force, leaving you with a smaller wing that only 'beachballs' to one side.

I could reach 5 kilos reduction with experimental setups, I do not think that is a lot, but the capacity can be reduced if you try to.

 

[The Chairman]

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.

You probably mean elasticity or more accurately Young's modulus. Tensile strength tells us how much weight it can hold before it breaks or fails. Since you are discussing pre-failure, then the elastic modulus and not it's limit, is what's important.

 

[cool_hardware52]

Since the wing cannot 'unfold' with the bungee to tight the T-weight system is pressed into the wing, it's not the lead volume, it is pressed against the wing with force, leaving you with a smaller wing that only 'beachballs' to one side.

I could reach 5 kilos reduction with experimental setups, I do not think that is a lot, but the capacity can be reduced if you try to.

You are mixing two phenomena. Very tight bungees can of course reduce the effective volume. The presence or absence of ballast on the "T weight" system will have a trivial impact on available wing volume.

Tobin

 

[Razorista]

With 14 kilos attached at the moment I press into the wing much more than with less, it is an uncomfortable bulk and is about half as much added volume as my body.
I totally agree otherwise.

 

[wetb4igetinthewater]

View attachment 368149

Not to divert from the argu.. ahem .. discussion, but I found the placement of the weights in the picture interesting. I just picked up a brand new Halcyon Contour from a friend that wasn't using it (too good of a deal to pass up, even though I won't dive it until the end of the year). He made some modifications for adding weight. I'll remember what you have done here for placing weights on your sidemount rig.

 

[decompression]

Not to divert from the argu.. ahem .. discussion, but I found the placement of the weights in the picture interesting. I just picked up a brand new Halcyon Contour from a friend that wasn't using it (too good of a deal to pass up, even though I won't dive it until the end of the year). He made some modifications for adding weight. I'll remember what you have done here for placing weights on your sidemount rig.

You can use a bit of bungee to secure the weights while testing. Remember to pull the knot under the weight as the last step of the picture.

 

[DevonDiver]

You probably mean elasticity or more accurately Young's modulus. Tensile strength tells us how much weight it can hold before it breaks or fails. Since you are discussing pre-failure, then the elastic modulus and not it's limit, is what's important.

Thanks... I had used the wrong term.

 

[wetb4igetinthewater]

You can use a bit of bungee to secure the weights while testing. Remember to pull the knot under the weight as the last step of the picture.

Thanks! Love the profile pic. I'm going to have to steal that for doing intro's with students.