BCD for Drysuit Diving

[PoseidonsEnforcer]

Curious if folks switch BCDs when diving wet vs. drysuit diving and if so, if they have any recommendations for a BCD for a dry suit.

I am finding that my Scubapro Knighthawk seems to restrict airflow in my drysuit, especially when I snap the chest strap, which seems to keep the air in my torso/legs rather than my upper body. This has been causing a few venting issues even with my valve completely open. I guess the simple answer would be not to use the chest strap But I would like to hear from others.

It might be user error too, since I've only been diving dry for just under a year. Do you think my knighthawk is just on too "tight", or are there better BCDs for drysuit diving? I could see something like the Scubapro X tek pure tek system working well with a drysuit.

My "specs" are-
5'8" 150lbs
USIA Techniflex
Scubapro Knighthawk 4lbs on each side for trim, 11lbs each side for regular weight
Blue Steel Faber 100

 

[tbone1004]

Surprised you need that much weight, but if you're in for buying new gear
DRIS Dive Gear 28lb BP/W System | Dive Right In Scuba - Plainfield, IL - Dive Right in Scuba
That will also drop somewhere in the 11-12lbs of weight off of your current rig, help with trim, and you won't have any airflow issues.

 

[krawlings]

I would have to say you have it to tight . Do you use a crotch strap ? If not try putting one on and loosen up the waist and shoulders just a bit. The crotch strap will keep the BCD from rising up .I would not cinch up chest strap much. Just enough to keep the shoulder straps from moving off my shoulders . When I dive dry as I ascend I have to start early letting out air about Avery 6' or so to stay ahead of the expansion of air.I usually ascend in a horizontal position . So I find air venting is slower to respond to my action of rotating to my right and left elbow up

 

[RJP]

You're probably wearing your BCD too tight and/or it is not of the correct size to wear with the increased thickness of your drysuit/undergarments.

Best regards,

Ray Purkis

 

[ajduplessis]

Have tried diving without the chest strap? The KnightHawk is a great BC. I also think that you are wearing the BCD to tight, try a looser setup.

 

[Colliam7]

Curious if folks switch BCDs when diving wet vs. drysuit diving

Yes.

and if so, if they have any recommendations for a BCD for a dry suit.

Steel backplate! I started drysuit diving with my Zeagle Ranger. I could adjust the size, but I required A LOT of weight - much like the 30 lbs you say you require. I hated carrying that much added weight. Moving to the backplate not only dropped 6 lbs from my weight pockets, it dropped even more because I was no longer tagged with the added positive buoyancy of the 'soft' BCD. Moving from an AL cylinder to a steel cylinder also helped.

I am finding that my Scubapro Knighthawk seems to restrict airflow in my drysuit, especially when I snap the chest strap, which seems to keep the air in my torso/legs rather than my upper body. This has been causing a few venting issues even with my valve completely open. I guess the simple answer would be not to use the chest strap But I would like to hear from others.

Your BCD is possibly, as several have already stated, too small. If you have it loosened to the maximum, and still experience what you describe, it is likely that you need an alternate BCD system for your drysuit.

 

[PoseidonsEnforcer]

Do you use a crotch strap ?

There is one on my drysuit, but no crotch strap on the bcd. I also think I can drop a few lbs of lead, which might help. I do dive faber 100 steel.

 

[DeputyDan]

I took the dry suit class with NWGratefulDiver on this board and used my Jacket BCD.

If I were to dive a dry suit on a regular basis I would definitely go with the BP/W set up.

 

[Crush]

I dive a BP&W (with crotch strap) and have never had problems with it restricting airflow in my drysuit.

My BP&W does not have a chest/sternum strap. When I adopt the "Superman" posture (arms out in front) in horizontal trim the BP&W sits comfortably on my back and there is no need for a chest/sternum strap. Putting my arms out in front stretches snuggs the unit nicely to my body. Try not using the chest/sternum strap?

 

[TSandM]

It's actually fairly difficult to restrict the airflow through a dry suit. And especially if you are anywhere near horizontal, most of the air is going to try to go to your BACK, not your chest, so I doubt a chest strap is really causing any problems at all. But it is true that a dry suit tends to be much bulkier than a wetsuit, so the same BC may not fit well -- that's more of a problem of diver comfort than gas transfer, though.

It can take a while to master the art of moving air around in a dry suit. You really have to be much more aware of potential buoyancy changes, and be much more proactive about getting ready to vent, than you do when you are using your BC for buoyancy. Air in the dry suit can get a long way from the only vent (Google "dynamic instability" and you should come up with an article about just this). Trim is much more important in a dry suit, because diving feet up will make it very difficult to vent, and diving head up will make it hard to keep any air in the suit.

The biggest reason for considering a BC change, in my opinion, is total ballast. A dry suit with undergarments is going to require more lead than a wetsuit, and more lead means more to carry around on land or up a ladder. Using a backplate means you get rid of up to 3 pounds of positive buoyancy from a padded BC, and you put 6 pounds of ballast on your back, reducing what you need to carry in weight pouches or pockets. But with dry suit diving, it's also sometimes very desirable to have some weight out at the end of your legs, which is why you see so many dry suit divers using negative rubber fins with metal spring straps.