SMB: Closed vs Open circuit?

[mark01]

I wonder if those of you who have regularly deployed one of these critters at depth have any preference between open vs closed circuit design. In thinking inflation through, it would seem that an open circuit smb (inflated at the open bottom) would be pretty simple to deploy at depth, but might not be quite as easy to keep inflated and visible at the surface, while the closed circuit design (using a valve to inflate) would might be just the opposite - a skill to master at depth, but would remain inflated at the surface more easily.

I've used my closed circuit SMB a time or two at the surface with no issues, but I anticipate diving in conditions which will require me to blow a bag at a my safety stop so the boat an locate me before I drift too far to be seen/heard. I think those of you who've done Scapa Flow might know what I am talking about here.

TIA

Mark

 

[*Floater*]

Have you considered buying a semi-closed SMB? (Can be inflate from bottom like an open bag, but only lets air in, not water (in theory at least)).

For primary I use a semi-closed SMB (orange/red). For backup I have a closed bag (with OPV) - yellow for communication purposes (tech dive thing). I chose a closed one for backup because it was cheaper and smaller (fits better in my pocket).

 

[DA Aquamaster]

I have used open, closed and semi closed. In my opinion, the latter works best.

Open circuit bags can dump at the surface. Closed circuit bags require a QD fitting to inflate - either from a short one on a stage or deco bottle for that purpose or from your wing or drysuit - and while it is not hard, disconnecting things underwater never struck me as smart.

A semi closed bag will not dump on the surface and can be inflated like an ordinary open circuit bag via exhaled air, your primary reg, your backup reg or from the air in your wing via the inflator exhaust button. I prefer the latter.

You pinch and edge of the bag between the knuckles of your index and middle fingers and hold the inflator with the rest of your fingers while the other hand keeps the reel or spool and line away from any potential entanglements. Since the air goes from wing to bag your buoyancy does not change. Once the wing is empty, you can add a bit more to the bag by pressing both the inflator and the exhaust button and the air more or less goees straight into the bag. Once you begin to overcome inertai and move upward from the extra lift, just release the bag. A quick shot of the inflator will ad air to the wing and get you back to neutral buoyancy.

A closed circuit bag does not give you that option.

 

[tedtim]

The DAN SMB has both options. Even when diving in a wetsuit I still have my drysuit hose on the regulator. It is safely tucked away beside my inflator. When it comes time to inflate the SMB, I use the drysuit hose to give it a shot of air to inflate. No problems with control because it can be done with one hand. No need to dump air.

While using a drysuit it is easy enough to disconnect the hose, use it to inflate the bag, then reconnect afterward.