Technique for Shooting an SMB

[Doc Harry]

Exactly how do you gracefully shoot an SMB from depth without getting dragged upwards? I have tried it about a dozen times and I'm still not happy.

I have a 6-foot Halcyon closed-circuit Dive Alert Marker that I inflate with my LP hose and send up with a finger spool.

The problem is that I start getting dragged upwards before the SMB has really inflated very much. I figure that, at 60 feet, I only have to inflate it about 1/3 full to get max inflation at the surface (66 feet = 3 ata).

However, long before I get even that much inflation I am on the express elevator upwards and I have to let the SMB go prematurely. (Okay, no funny comments here about premature releases....)

I tried exhaling just before so that I am negatively buoyant as the SMB inflates, but this doesn't work either.

The best I can do is to get dragged up only two feet before I release and end up with a half-inflated SMB at the surface. Maybe I just need more practice?

 

[jagfish]

Hi Doc

When using the drysuit hose, I get a little negative with an exhale and then inject air in until I feel like I am getting positive then let it go. I don't really worry about how full it will be when it gets to the surface.

 

[Orlando Eric]

The easiest way is to get a 4000 psi ball valve and hook the hose up to a spare high pressure port. That way instead of a whimpy 150ish PSI you get a nice 1200~3000 psi squirt at the end of dive depending on how much PSI you have left.










JUST kidding.. DO NOT try that.

 

[Doc Harry]

JUST kidding.. DO NOT try that.

NOW YOU TELL ME!

 

[double80s]

You depth and the lift of the marker are going to play a big part in this as well. If the marker has a lot of lift, you may not be able to fully inflate it at that depth without running into the issues you're having.

The elevator ride is alway fun. I quickly learned to abandon shooting bags/sbm it with a safety reel in favor of using a spool. Much safer!

 

[TSandM]

My Fundies instructor said he vents a little air from his BC just before he inflates the SMB, in anticipation of the extra buoyancy he's going to get while holding onto the bag until it's released. He can do that smoothly . . . it's not quite as easy as he makes it look.

 

[RICHinNC]

Another question in this realm then.....

Why do you need to deploy it....while you are deeper than you plan to hang on it?

I mean....if you are going to hang on it at 20 ft for a deco....or whatever depth...why would you want to deploy it deeper than the depth?

I can see a spool being very handy and care must be taken so as not to get snared in the out going line. Plus I can see practice surfacing and taking in all the deployed line is a good value.

 

[matt t.]

I would (and do) inflate the bag "orally" instead of using the l.p.inflator, which makes for a slower and more controlled "bag shoot". You can also let go of the spool (delrin) while it is spinning and it will spin right in front of your face, however (this is a BIG however) as soon as the smb hits the surface and the spool will unroll to the bottom. If you MUST use the inflator hose to shoot the smb, do so with SHORT bursts. You don't have to fill it up, you just need enough air to get it to the surface. Good luck .

 

[dherbman]

I'm guessing tidal volume can account for about 6-8 lbs of buoyancy. I think the trick is to be efficient enough in filling the SMB that it can be accomplished during a single exhalation. This way, it is more like an exchange of volume, rather than an increase.

Shooting from a horizontal orientation presents a larger surface area to the water column which will reduce the immediate effect of positive buoyancy and also allows you to fin downward using a frog kick. The tricky part is paying attention to your buoyancy while dealing with the SMB and compensating before it becomes an issue.

Know when enough is enough can also be an issue. Inflate the SMB ao that it will have just enough air in it when it arrives at the surface.

Practicing at depth will make the task easier. Starting at 30' will be a lot easier than starting at 15'. It will require less air in the SMB at 30' to arrive at the surface with a proper fill than if you shoot it from 15'.

 

[dbulmer]

RichInNC,
In the UK you almost always have to put up a DSMB - the skipper needs to know where you and your buddy are - our conditions dictate this by and large.