BCD with Dry Suit?

[Rainer]

For Buoyancy control, you must use the BCD.

Absolutely silly. If you dive a properly balanced rig, for singles, you start the dive negative only the weight of the back gas (about six pounds for most common sized cylinders). The gas needed to offset that weight is about what you'd have in the suit anyway to keep it comfortable.

 

[muddiver]

Using the suit for buoyancy will only really work well if you have a light load of lead weight. Typically you need quite a bit of weight to stay at your safety/deco stop at the end of your dive and you are usually more buoyant from the use of you breathing gas. Subsequently, you start your dive so heavy in a dry suit that the suit it self will probably not be as effective as your BC, even though the air you add to the suit for warmth/squeeze reduction will add to the effectiveness of the BC.

I have used the suit for buoyancy and it does reduce task loading dramatcally, but I also had a smaller suit at the time and I use realitivly thin underwear.

 

[muddiver]

For Buoyancy control, you must use the BCD. The only reason to put air inside the dry suit is to stay warm and to avoid being pressed at depth.
You should use a minimun amount of air inside your dry suit, just to feel comfortable and avoid folds of the suit which will mark your skin under pressure.
As any air space, it will reduce the volume with depth and increase volume as the depth reduces, so if you add some air at the botton, you have to release that air as you go up, to avoid uncontrolled bouyancy.
If you keep the air inside the Dry suit at a minimun, you do not need to think twice when going up. Finally, the dry suit vent valve has 2 positions : manual and automatic. If you leave it in automatic, as soon you go up, it will release air to avoid over-expansion. The counter point to this is that they normally leak in automatic. More often if it's a rented DS. In manula you have to release the air inside.

I have never heard of a "Automatic and Manual" exhaust valve. All of the valves I am aware of are automatic with a selection of how much pressure it will hold before release, or fully manual if you have an old suit.

 

[DCBC]

Given the scope of training and experience of today's recreational diver, I agree with what's been said. I want to suggest however that not using a B.C. with a Dry Suit is not necessarily an unsafe thing to do. Commercial Divers seldom use B.C.'s (restriction of movement) and in some circles B.C.'s are considered unsafe. I'm also not willing to say that for the first 25 years of SCUBA diving that all divers were unable to dive safely. Back then an inflatable vest (CO2) was sometimes used, but provided limited assistance for surface rescue only and not buoyancy control. You were taught to drop your weight belt to achieve positive buoyancy in an emergency situation and to be within touching distance at all times with your buddy. I know that technology has taken over our society, but the standards and practices today leave much to be desired. Don't get me wrong, I'm not against equipment progress, but students and Instructors were better trained 30 years ago.

 

[Bubbletrubble]

I have never heard of a "Automatic and Manual" exhaust valve. All of the valves I am aware of are automatic with a selection of how much pressure it will hold before release, or fully manual if you have an old suit.

@muddiver: The instruction manual for current-version Si-Tech automatic exhaust valves states that when in the fully closed position, the user can still vent by pressing down on the dump valve. In my personal experience with this brand of exhaust valves (over the last 4 years), this has certainly proven to be the case. Si-Tech valves are quite popular on the drysuits I see here in the San Diego area. I don't doubt, however, that some older designs of exhaust valves are fully manual.

 

[muddiver]

@muddiver: The instruction manual for current-version Si-Tech automatic exhaust valves states that when in the fully closed position, the user can still vent by pressing down on the dump valve. In my personal experience with this brand of exhaust valves (over the last 4 years), this has certainly proven to be the case. Si-Tech valves are quite popular on the drysuits I see here in the San Diego area. I don't doubt, however, that some older designs of exhaust valves are fully manual.

Yes, and believe it is the same with most dry suit dump valves that are available. But, they are still considered automatice valves. Screwing it down just adds so much closing force from the internal spring that it will not vent on its own. Allowing for manual overide is a very important safety feature.

 

[fdog]

The typical learning progression:

1) Take dry suit class. Learn the quick-and-dirty way, which is to use the suit for everything.

2) Dive for a while. Have a couple of "flail moments" with excess air in suit almost getting out of control.

3) Talk to more experienced divers. Make huge, other-side-of-the-pendulum switch to using just the BC for buoyancy control.

4) Do lots and lots of dives.

5) Eventually realize they have, slowly and unknowingly, become "hybrid buoyancy" divers - use the BC for huge chunks of buoyancy, like backgas loads, and use the suit for very small, ounce-by-ounce trim buoyancy adjustments.


All the best, James

 

[Sas]

Using the suit for buoyancy will only really work well if you have a light load of lead weight.

Hmm I don't agree and I don't agree with all the posters who say that you shouldn't use the suit. As C-Stone says it is really personal preference and there is no right or wrong way. I listened to all that guff initially about not using the suit because it would make my trim crap and would be hard to manage, etc etc and as a result I only used my suit to offset squeeze for the first season in my drysuit. These days I overweight myself by about a 1kg, and put more air in my suit and rarely use my BC these days for buoyancy when I am diving dry. I am infinitely warmer these days using this method. Also my trim is fine and I really do not find it difficult to manage the air in my suit at all Though if it is a short dive where I am unlikely to get cold then I'll use the wing.

Experiment with both methods - they each have their pros and cons (the main one for me is that my drysuit vents slower than my BC so I have to be more on the ball when ascending but that's about it). And see what you prefer.

 

[joolz]

I rarely use my BCD for buoyancy control underwater...it's pretty much for surface swims only. I would, however, caution against doing away with the BCD entirely. I had a neck seal break during a dive -- a drysuit class, ironically enough -- and ended up with a full flood. Being the trooper that I am, I finished the class but kept it to the minimum 20 minutes. Because it's a shell suit, it has no buoyancy when it's filled with water...and if I didn't have a BCD, I would've had to either dump my weights or walk back to shore along the bottom.

With OW students, we suggest adding air to the drysuit only to offset the squeeze, and to continue using the BCD for buoyancy. With drysuit students, we get them to start playing around with the suit to figure out the different buoyancy characteristics, and use whatever combo is most comfortable. It's generally easier/faster to dump air from a BCD than a drysuit, especially if it's a rental suit that doesn't fit properly across the shoulders.

 

[johncayce]

Ok so here is a question. Since air in a dry suit acts as an insulator against the cold water, would more air keep you warmer? By that I mean using the dry suit for bouyancy contol.