BCD with Dry Suit?

[CalgaryDF]

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.

Not having enough air in your drysuit will really reduce the thermal properties of your undergarments. When I dive in colder water I try to carry and pound or two extra so I can get a little more loft in my undergarments and stay a little warmer. OTOH putting tons of air in your suit (more than required to have full loft in undergarments) probably won't keep you any warmer and will likely be difficult to manage in your suit.

I generally find that the air required to offset the squeeze plus a little more is all that I need to be neutrally buoyant. The "bubble" in my suit is not big and moving all over the place so I don't really use my BCD. If I'm overweighted for some reason, I find that the BCD is essential to maintaining control over my buoyancy because adding too much air to my drysuit makes it difficult to manage.

 

[Sas]

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.

You need enough to loft your undergarments (and that can vary depending on what type of undergarments you have) but I doubt more than that will have much of an impact. If I don't add a bit of extra weight I don't need any air in my suit or BC for many dives that I do so I get cold. Having a bit of a bubble in there can also help to adjust trim, you just move it around to reposition yourself.

 

[Kingpatzer]

The problem with using the suit for buoyancy for most divers is that you have to control the air bubble. You'll actually be able to feel the air move around in your suit if you really pay attention. Exclusively using the suit makes maintaining trim more difficult.

But you do need to put a bit of air in the suit to keep yourself warm and avoid trim. Finding the balance between enough air in the suit to avoid squeeze and stay warm while at the same time not getting so much air that you have trim problems, and using the BC from there is something that comes with time.

A lot of people who say "use the BC" miss that they are using the suit too - they can't help but doing that, even if the main reason they put air in is for warmth and squeeze. On the other side, I've yet to see a "suit only" diver (almost exclusively these have been new dry suit divers) with anything approaching descent trim in a dry suit. (of course, they tend to have lousy trim anyway, so it's arguable that it isn't the dry suit )

 

[joolz]

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.

The primary purpose of a drysuit is to keep you dry. While neoprene may slow heat loss, it's ultimately the thermal underlayers which keep you warm. When your body heats up the air around it, the underlayers trap the warm air so that it doesn't immediately get cooled down by the inside of the suit. More air isn't necessarily better since it means your body has to work harder to heat it up, and it may actually cool faster due to increased circulation within the suit.

That being said, the amount of air we're talking about for buoyancy control isn't going to create a giant bubble around you. Compare the volume of a full BCD with the volume of a drysuit -- if you're properly weighted to begin with, it would only amount to a thin layer of air over your entire body surface. This shouldn't be enough to have a noticeable effect on warmth.