Drysuit or BC for Buoyancy? BC of course!
When using a drysuit divers will need to add air to their suit on descent to avoid the accompanying, potentially painful, squeeze that is explained by Boyle’s law and the associated increase in pressure. Since drysuits themselves provide little or no thermal protection, insulating underwear is required to prevent hypothermia. This underwear needs a certain amount of loft to be effective. So, as well as adding air to avoid squeeze, divers must also add air on descent to maintain loft and remain warm.
All the air added should be there solely to equalize the compression that occurs with increased depth – the diver is equalizing the airspace inside the suit in order to remain comfortable and warm.
Additional adjustments may be required for buoyancy control and these should be made by adding air to or subtracting air from… the Buoyancy Control Device (whether that is a traditional BCD or a bladder/wing).
Drysuits should not be used for buoyancy control – they are suits that keep you dry whilst Buoyancy Control Devices, well, they are just that.
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What a total load of toss, has this person ever dived a dry suit ???
regards Baz
Yeah, I think I have to disagree too. You can compensate with your BCD if you change your configuration underwater or if you’re carrying lots of negative tanks so you need extra lift but generally when you compensate to avoid squeeze you also compensate your buoyancy. The two issues change at the same rate. The only reason you have to add air at depth is because the volume of air in your suit gets smaller so you lose buoyancy. Correct one and you inadvertently correct the other.
BCDs are critical when you’re diving dry incase your suit floods leading to a catastrophic loss of buoyancy or in the event that you’re getting negative and your inflator fails. Suits contain so much air that when they flood the loss of buoyancy is pretty extreme.
One more thing, trilaminate (shell) suits have no inherent warmth but neoprene drysuits do. Thick neoprene suits lose some of their natural buoyancy at depth so that may be another reason why a little tweak of the BCD may be better sometimes.
Using a BCD when you don’t need to just makes things more complicated. Its harder to figure out where to release air from on the way back up.
I think Rick brings up a valid point. Baz and Andy disagree.
For me, the way I was trained and my preference now is to use the Bladder or wing for buoyancy control and my dry suit as thermal protection. Usually the amount of air added to your dry suit to provide enough loft for your thermal protection to be effective is about the same amount of air needed to prevent suit squeeze. I concentrate maintaining my neutral buoyancy control with my wing.
To address some of the issues Andy brings up; should you have a catastrophic failure of your dry suit and it totally floods, you have no fears of buoyancy control if you are using your wing. Your only worry is getting cold, fast! Yes indeed, you can use your dry suit for emergency buoyancy control. You should train with that in mind. As far as releasing air from your dry suit, that is what the adjustable exhaust valve is for. It automatically vents at whatever pressure you set it at, it is not complicated at all.
Baz, I continue to dive with a dry suit in a variety of environments, I have some little experience. In my experience, this is a good way to do it. I teach it this way. But…. I encourage my students to choose the style, type and way they dive as they desire and makes sense from an efficient and safe outlook. Once they are out of the classroom (teaching environment), they are free to choose. But while training, it is the wing for buoyancy control.
Should you cave dive or dive at a particular depth for a period of time, you can see the logic at leaving the dry suit inflation alone (not much adjustment required for squeeze and loft) and use the wing or breath control to make adjustments in depth.
Hey, this is exactly what this site is about. An exchange of ideas by people who actually know about diving and actually dive. Be safe no matter what style of diving you do!
dean
@Baz If we were in Mos Eisley Cantina I’d have just chopped your arm off and your friend Murch would be scurrying away as I stood firm with a raised eyebrow (he’s easily persuaded, that one)! Just kidding; thanks for reading and posting your comments. To answer your question: yes; a big red one, lots of times and in various places.