Double vs. Single Bladder Wings (and bungees too).

[lamont]

The 60# Halcyon Evolve wing is really nice. Lets you load it up with double E8-130s and multiple deco and stage bottles just fine. The Evolve is also good for trim and has a donut shape which makes dumping easy.

I don't understand what problem it is that bungees solve. I guess if you've got a 120# wing they'd be useful to keep all the slop under control, but there the diver is falling victim to the "more is better" syndrome and may find out that in the event of a first stage IP creep failure into the wing that 120# of lift becomes a ticket straight to the surface. My 60# wing is going to be much more controllable and I can kick down against it being fully inflated...

 

[lamont]

Been there, done that...went into a wet t-shirt contest. If you have the right kind of undies, there is little to no lose of buoyancy.

For the readers who may not already know, what Jeff is alluding to is that thinsulate is hydrophobic and will retain its loft (and buoyancy) when flooded better than other material.

 

[RAD Diver]

Well I tried to order my DSS doubles rig today & who I talked to asked a lot of questions on lift I would need as far as rig & flooded DS. I thought it was down to 2 choices 50 or 70. I had no idea how to do this til I read this thread. I will be in my pool tomorrow checking out how much it takes to sink my DS & use the formula for rig Tobin provided.

 

[cool_hardware52]

Been there, done that...went into a wet t-shirt contest. If you have the right kind of undies, there is little to no lose of buoyancy.

Thinsulate insulation is not hydrophobic, it can be saturated, otherwise one could not wash it. Thinsulate fibercould be considered hydrophobic. The insulation materials are made from the fiber.

Thinsulate works because the fibers are very small, and the materials made from the fibers have very small "dead" spaces to trap gas. They still work by trapping gas, and this trapped gas can be lost. When the trapped gas is lost, and replaced with water the initial buoyancy is lost too.

I would agree that a total or even significant flood of a DrySuit is a rare event.

What most divers have experienced is a partial flood, one that gets the undergarment damp, maybe even soaked in spots, but is well short of a major flood. A dampened undergarment will not caused a major change in buoyancy.

What is unique about thinsulate insulating materials is that due to the very small voids created by the very fine fibers, a wet undergarment still provides insulation, because the water in the material does not migrate easily.

If you think a thinsulate garment can't get wet, submerge one in fresh water, and see if it's really heavy when you try to pull it out...............


Tobin

 

[cool_hardware52]

Okay so if I am fully understanding Tobin let me take this one step further and work the problem a bit differently.

Rig Weight w/gas is 35lbs
Rig Weight w/o gas is 19lbs (HP100 == 16lbs gas)

Dry Suit (DS) to be neutral the counter weight is 30lbs

So DS counter weight less Rig w/o gas is 11 lbs of additional lead.

If additional 11lbs of lead is on the rig w/gas it is now 46 lbs.

Then add the additional gas for the suit 5 lbs which for the sake of this exercise is also on the rig this brings the total for the rig to 51lbs as well. QED (?)


Now the last part that is not mentioned is that the cylinder weights are when they are fully submerged. If you want to any chance of floating above the water you probably want to have a bit more lift. Say with above one gets a 55 lb bladder. Is the additional 4lbs enough? Seems a little light to me ??????????????????

SS,

We might be on the same page, but I'm not sure I follow your approach.

It really is just as simple as I stated it. Your wing needs to be able to float your rig. The heaviset yoru rig will be is at the start of the dive with full cylinders, so your estimated rig weight should be with full cylinders.

In cold water is is almost never the weight of the rig that dictates the minimum required wing lift, but it's worthwhile to check. In warm water the weight of the rig often does dictate the minimum lift.

Now back to the "other" number. Does a diver need to be negative at the start of the dive, and if so by how much? For doubles I assume manditory deco is likely, so the diver needs to negative by at least the weight of his back gas. It's also nice to be able to add a little gas to the DS for comfort. Thats where I get the 16lbs (backgas) and 5 lbs (DS inflation gas) I used in my example. 16+5 = 21 lbs. The diver needs to be ~21 lbs negative at the start of the dive.

The other requirement is a means of compensating for the initial buoyancy of the exposure suit. Here we are assuming a DS that is 30 lbs positive.

If the diver were to start the dive weighted so that he was neutral at the surface with no gas in his wing and full cylinders, he could descend, but would be unable to maintain depth or deco stops as he breathed down his backgas. when he adds the 21 lbs of ballast determined above, he will need to inflate his wing ~ 21 lbs to stay at the surface.

That how I arrive at 30lbs of initial buoyancy from his suit + 21 lbs for backgas and drysuit inflation.

As previously noted using the full value of the DS initial buoyancy is very conservative, because it's very unlikely one could loose 100% of the buoyancy of their suit.


Regards,



Tobin