Question DSMB Question

[mdwalter]

Another question: You're supposed to look up before releasing your DSMB but what if visibility is poor?

If vis is so poor that you can't even see the silhouette of anything above you, you're probably better off not deploying a DSMB at all. Just wait until you surface and deploy your SMB. Also, if vis is that bad you probably should not be swimming mid-water in the first place but should be on an anchor line, a reel you ran from your entry/exit point or some other form of touch contact navigation aid that does not require you to see things you can't really see. In that case, again, there would be no need to deploy a DSMB, so don't.

 

[mdwalter]

A 6' DSMB might have 40 lb of lift if full. To deploy it at 10 meters and have it full at the surface you would have to fill it half full. 20 lb of lift. Not going to happen. I like to have a big DSMB because it is a backup flotation device. Since I don't want to carry two, I accept that it is just a bright thing that floats flat on the surface.

It only lies flat on the surface if you don't keep tension on the line. A 6' SMB that ends up only half full at the surface (1/4 full at 10m) will still stand vertical, though only 3' out of the water if you keep the line reasonably tight.

 

[mdwalter]

I think I have the same DSMB. Even though it's FAR easier to release it with a single breath at greater depth, I wanted to practice and get it working well at 12-15' in a pool. I had some free time while a DM I was practicing with was helping an OW class, so I played with it for about an hour while practicing keeping trim, sticking to depth, and getting a decent deploy at a shallow safety stop depth.

What finally worked pretty good for me was relaxing and focusing on breath control. What I would do is first chill, find some zen, dump most of my wing, and take a very large breath to completely full lungs, and then only breath out to about half full lungs, then repeat back to totally full. I made minor adjustments to wing inflation until I was absolutely neutrally buoyant, nearly motionless, and resumed that breath pattern for a while to make absolutely sure, just to get the really good feel for breathing slowly with very full lungs to about half full lungs.

Then I put a small puff of air in my dsmb to get it to unfurl, made sure I was chill with the spool and the line, and then when I was at the top of a breath, with 100% full lungs, I would breath out almost the full set of lungs into the dsmb, very chill, no hurry, no stress. When I put my reg back my cakehole to take another breath, I only breathed up to about half full. Didn't suck in a big lung full, just enough to keep a normal breathing pattern but shallow and low volume. Then I stopped filling the dsmb for a hot minute. I took time to make sure bouyancy was still stable (not messing with the inflator, just verifying I'm still hovering), controlled breathing between half full lungs and empty lungs. Not going anywhere, still neutrally bouyant, less gas in the lungs to offset the extra gas in the dsmb. Taking another breath up to about 75%, and you'll see yourself start to rise a just a little, dump that entire breath into the dsmb, and let it unspool and pop to the surface. Then I just put the reg back in my mouth and resumed breathing between about half full and totally full.

It wasn't perfect, but it worked pretty well and I had a big fully inflated SMB at the surface without an unplanned ascent. I'll play around with it some more in the quarry this spring at 15', will try it by just watching the depth gauge on my computer without the wall of the pool to work from.

To quote the Mandalorian, "This is the way."

 

[CnC]

Curious as to why you are not inflating with your alternate rather than "breathing several breaths" into the DSMB. We do not teach people to blow into the DSMB to inflate unless on the surface, but rather to use their regs to free flow into the base of the DSMB for this very reason. I also agree on the depth - I teach my students to deploy from 25 - 30ft to avoid these issues.

 

[steinbil]

If vis is so poor that you can't even see the silhouette of anything above you, you're probably better off not deploying a DSMB at all. Just wait until you surface and deploy your SMB. Also, if vis is that bad you probably should not be swimming mid-water in the first place but should be on an anchor line, a reel you ran from your entry/exit point or some other form of touch contact navigation aid that does not require you to see things you can't really see. In that case, again, there would be no need to deploy a DSMB, so don't.

With your line of reasoning - what function does a DSMB have?

In my world, it primarily serves 2 purposes:
1. to signal boat traffic to stay away
2. to let your surface support know where you are

In neither of these cases is the visibility underwater relevant. Furthermore, being able to swim midwater or doing blue water ascents with DSMB in poor visibility, is a skill I consider necessary for boat diving. Relying on an anchor line as the only way of ascending seems like a bad idea to me.