Twins with only drysuit for buoyancy

[D_B]

....

One big issue they don't touch on is dealing with a runaway ascent. If you have a big bubble in the suit and you find yourself ascending too quickly the valve might not be able to vent quick enough - result, burping the neck seal and possible flooding. I haven't had that problem but I have seen others flood just that way.
With a smaller bubble in the DS the valve can keep up and the BC can dump air far faster than the DS.

All this is just my experience and I'm not disagreeing with PADI, I keep spending money there. It's their agency and they can make their rules any way they want but, I have to admit... I don't wear a snorkel on my mask either :shocked2:

I would like to point out here that my class was by PADI and that is one of the skills that was stressed by my instructor, in fact he would not pass you if you could not disconnect inflator, right yourself from a head down position, pull open a neck seal, with gloves and hood on, reconnect, and return to a hover .... all this without reaching the surface from starting at 8 feet, and after the instructor held the inflate valve on your suit for the count of three before letting you go. ... http://www.scubaboard.com/forums/advanced-scuba-discussions/260824-padi-dry-suit-class.html

One other reason to train with just suit for buoyancy is that with more air in your suit, it's touchier on trim and air transfer ... if you can learn to handle with it that way, then with less air it will be easier

Edit: sorry for the hijack

 

[DaleC]

pull open a neck seal,

I think we all did the same drills but I won't really risk doing that in 39*F water with a long surface swim to shore.

One other reason to train with just suit for buoyancy is that with more air in your suit, it's touchier on trim and air transfer ... if you can learn to handle with it that way, then with less air it will be easier

Which is the point I was making, It's easier to maintain trim with less air in the DS which is how I like to dive it.

But, to each his own. Both the DS and BC are just water proof bags that hold air. Using one or the other for bouyancy isn't that big of a difference. If it is then probably the diver needs to practice some more skills.

 

[sschlesi]

I have to agree with AG under some conditions. When a dive profile is going to have a constant bottom depth, yes, but in the case of a cave dive if the profile of the cave goes up and down, no. Under these conditons you waste so much gas venting the drysuit and blowing it back up, then venting again.

I don't think there should be a difference between venting/filling a BCD or a DS on the same profile. 1 unit of air in the BCD displaces the same amount of water as 1 unit in a DS.

 

[String]

The "dump from neck seal" and "dump from wrist seal" methods suggested i wonder how many people could actually do these in practice and in a sensible amount of time. Certainly by the time ive fitted my thick hood and put on thick gloves i cant reach my neck seal to pull it free.

I couldnt do my wrists as my wet gloves more than cover the seal area to stay warm or im wearing dry gloves.

 

[Reg Braithwaite]

I don't think there should be a difference between venting/filling a BCD or a DS on the same profile. 1 unit of air in the BCD displaces the same amount of water as 1 unit in a DS.

My experience is that while air is air is air, the suit trims differently and vents differently and inflates differently from the wing. So I got some value from practicing a variety of dives using the suit for buoyancy.

 

[budgy]

There are many who put some air into the suit but principly use the bcd/wing during a dive for buoyancy, the choice is theirs. I've tried both. There's less task loading using one source of buoyancy control. As you have to put air into a dry suit to prevent suit squeeze, with singles twins or rebreather most people I know control buoyancy with their dry suit. The first time I went over 40m I felt it was necessary to use the suit and the wing/bcd I was overweighted. I suppose dive style has much to do with it. If you dive negative and use momentum you move through the water faster and have a slightly better SAc rate and your unlikely to have an uncontrolled buoyant ascent, but you sink when you stop. I'm an underwater blimp. Many dry suit divers dive without a wing/BCD and use suit inflation only. A back pack, single cylinder and suit inflation is a very popular style with commercial shell/solo divers. Whilst most use a lift bag these shell divers have no problem lifting themselves along with large quantities of shell fish with just their suit for buoyancy although it probably does put considerable strain on their suit seams. As for suit flooding, I've had many wet dives in dry suits. Water weighs nothing in water. I've found dry suits that leak like sieves will still hold enough air for neutral buoyancy and the neutrally buoyant diver only needs a single deep breath to start an ascent. I've known some people dive twins without a wing/bcd, I've never tried it. I dont think its that convenient, particularly if your going to take your twins off in water to get into a rib.

 

[SuPrBuGmAn]

Getting away from the typical realm of diving... apparently sump divers regularly dive twins(smaller sized tanks though) with just the drysuit as bouyancy control.

 

[Melicertes]

As to the OP's question,,,is he asking if it is OK to dive with NO BC/WING? Only a drysuit? If that is what he is asking - NO !

My instinct tells me that strapping on a set of doubles and just relying on the dry suit for buoyancy is a Darwin Award waiting to happen because there would be no backup buoyancy device in case something goes pear shaped. Everyone I have seen diving doubles dived with dry suits with some sort of additional buoyancy device (whether wing or jacket style,) and even though this might be coincidental I've always assumed that this is:
1. for redundant buoyancy in case the dry suit fails for whatever reason - the BCD is still there to assist in getting to the surface in a controlled manner with those doubles on their backs, and
2. for exposure protection purposes due to extended bottom times where neoprene would not be sufficient enough for a comfortable dive and the dry suit would not provide the same inherent buoyancy characteristics of the neoprene to make it easier to ditch weights in an emergency and get to the surface.

Since the poster I quoted put on his profile that he has been diving since the early 1980's I felt that his philosophy of tossing out the BCD entirely from the equation is either a case of that's what he's been taught and he never bothered to think about the logic of it, or I'm missing something and because I have no experience with doubles I'm not seeing the whole picture here and therefore my gut feeling that tossing the BCD back into the gear bag, or not even owning one from the sounds of it, is off base. That's why I chose to post it up here to find out what you guys all think about it.

As a student I never learnt about the potential problem with steel tanks and neoprene suits on deep dives until I joined SB and read some articles on here about it and I've been diving my 15L steel for years until I brought it to the US and discovered it is now useless because it is not stamped by the DOT and I can therefore not get it filled (anybody want to buy a 15L Steel Farber in excellent condition? ). Since I will be going the twins route eventually, albeit not in the near future, knowing if the "toss it out" philosophy has some merit to it or not, is good to know.

 

[D_B]

The "dump from neck seal" and "dump from wrist seal" methods suggested i wonder how many people could actually do these in practice and in a sensible amount of time. Certainly by the time ive fitted my thick hood and put on thick gloves i cant reach my neck seal to pull it free.

I couldnt do my wrists as my wet gloves more than cover the seal area to stay warm or im wearing dry gloves.

We had to wear the gloves and hoods that we would normally wear here while doing it (5mm and 7mm respectively for me)
... man does that suit lose air fast when you do the neck seal

Water in your suit does not weigh anything in the water, it's the loss of lift that comes with a massive suit flood like zipper failure that is a problem, especially if it happens at the beginnig of a dive with full tank(s)

 

[TSandM]

Water in your suit becomes an issue when you get to the surface and you're trying to keep your head above water. Your BC doesn't really want to lift sodden undergarments very high. My drysuit flood experience is the only time in 700 dives that I've thought about ditching weights at the surface.