Reducing the length of my DSMB

[HIGHwing]

Try this...

At depth take your low pressure inflator and dump all your lift into the bag. While still holding onto the bag, continue to inflate the bag by simultaneously depressing the dump and inflate buttons. When the bag is too buoyant to hold down let it go and just add back buoyancy to your wing. Guarantee you get some gas in the bag using that method.

 

[Wookie]

Or try this: AP Self Sealing SMB with Inflation Cylinder | AP Diving

That SMB with inflation cylinder is the best thing since sliced bread. You don't have to worry about buoyancy issues, or breathing, or taking a regulator out of your mouth. Hook the SMB to your reel and twist the valve. Easy-peezie.

 

[DevonDiver]

Or try this: AP Self Sealing SMB with Inflation Cylinder | AP Diving

That SMB with inflation cylinder is the best thing since sliced bread. You don't have to worry about buoyancy issues, or breathing, or taking a regulator out of your mouth. Hook the SMB to your reel and twist the valve. Easy-peezie.

I used to own one. I had nightmares about it inflating on me, at depth, clipped on, with a heavy deco obligation. I sold it.

 

[raftingtigger]

This is actually getting quite amusing - especially since this in a supposedly sophisticated forum. Maybe I didn't communicate my question well at the outset, or maybe most of the posters didn't fully read and/or comprehend my question. Most likely it was both.

I did NOT ask:

1. How to deploy a DSMB. I have tried or at least considered all of the suggestions given so far. After much experimentation I have settled on the one breath oral inflation method as the best for ME.
2. Which length of DSMB to use. Given the dive sites and conditions I will be diving a DSMB any length equal to or greater than 1 meter is adequate.

I did ask 1 question:

1. Since I want to use a lower volume DSMB than I currently own for XYZ reasons what problems or failure modes are likely if the DSMB is rolled down and secured with rubber bands as shown in the picture.

To summarize the useful information given:

1. It might be top heavy. This is easily tested.
2. It might unroll. Also easily tested and a benign failure mode.
3. No one likes the idea. Which means my instructor is likely to disapprove the idea. This is a compelling reason to not try this - at least for the class.

Other negative reasons not explored:

1. Entanglement hazard rolled. It is not.
2. Entanglement hazard when deploying. Possibly, especially with kelp. Definitely something that needs evaluation.

I would like to thank those posters that did contribute answers to my question.

To all the others, you may now hijack this thread and give advice on both how to deploy a DSMB, and what size DSMB is best for what conditions.

 

[scjoe]

I used to own one. I had nightmares about it inflating on me, at depth, clipped on, with a heavy deco obligation. I sold it.

The Brits I know seem to be big fans of the AP and claim it can't self inflate. Never having seen one in person, I'm not sure what prevents this from happening, but I've never heard of one doing so. Could you explain what has to take place for the device to self inflate?

 

[FinnMom]

If I were your instructor, I would make a point of giving you my SMB to send up. The skill is to be able to launch an SMB, not just one special SMB you have modified to be easier for you.
You asked about possible problems and failures with your proposed solution. Thing is, your solution/focus IS the problem => the whole point is to learn the skill, not the use of one bag. The people telling you what you don't want to hear (how to launch...) are trying to tell you how to get what you want (you = skilled smb launcher). If their methods don't work the solution is practice.

 

[Wookie]

I used to own one. I had nightmares about it inflating on me, at depth, clipped on, with a heavy deco obligation. I sold it.

Were you afraid the valve would roll on? I do stow mine so the little cylinder is on the inside of the roll, but the valve is pretty stiff....

Whatever, to each their own. That particular SMB is a gear solution to a skills problem. Just what the OP asked for.

 

[rjack321]

This is actually getting quite amusing - especially since this in a supposedly sophisticated forum. Maybe I didn't communicate my question well at the outset, or maybe most of the posters didn't fully read and/or comprehend my question. Most likely it was both.

I did NOT ask:

1. How to deploy a DSMB. I have tried or at least considered all of the suggestions given so far. After much experimentation I have settled on the one breath oral inflation method as the best for ME.
2. Which length of DSMB to use. Given the dive sites and conditions I will be diving a DSMB any length equal to or greater than 1 meter is adequate.

I did ask 1 question:

1. Since I want to use a lower volume DSMB than I currently own for XYZ reasons what problems or failure modes are likely if the DSMB is rolled down and secured with rubber bands as shown in the picture.

To summarize the useful information given:

1. It might be top heavy. This is easily tested.
2. It might unroll. Also easily tested and a benign failure mode.
3. No one likes the idea. Which means my instructor is likely to disapprove the idea. This is a compelling reason to not try this - at least for the class.

Other negative reasons not explored:

1. Entanglement hazard rolled. It is not.
2. Entanglement hazard when deploying. Possibly, especially with kelp. Definitely something that needs evaluation.

I would like to thank those posters that did contribute answers to my question.

To all the others, you may now hijack this thread and give advice on both how to deploy a DSMB, and what size DSMB is best for what conditions.

Funny how you haven't even taken the class yet but you know:
1) the best way to inflate it
2) that you need a lower volume SB and that it will work for your tech diving (note that you have yet to actually do a Tec40 dive anywhere except the internets)
3) you are too cheap to just buy a smaller SMB
4) that your instructor will recognize your cheapassness as a valuable tech diving attribute and commend you for your ingenious modifications and thereafter allow your rubber banded SMB in the course.

Rolling up either the top or bottom of a bag is rather pointless, you need to pull down on the line to get it to stand up no matter how tall it is. If its not fully inflated some additional uninflated material will be below the surface.

Hint you will end up with at least 2 different SMBs if you pursue actual tech diving after your course, a small one and a big one. Maybe ask your instructor if he (or she) has some you could try for the course so you have a greater depth of experience with which to choose appropriate ones. That's what the course is for afterall.

 

[UnixMarine]

IMO, the way this thread has gone is scary. According to the title under your name, you're a dive master. That means you are someone new divers look to for guidance and help. This puts on us a responsibility to learn to do things properly and be the absolute best divers we can be. Shooting an SMB should be a skill a dive master is practiced at and can do with no problems, even if he is not familiar with that particular SMB. It gives me great concern that you are essentially (as it was put earlier) looking for a gear solution to a skills problem. Practice, practice and more practice is what will do this for you. As has been said, trying to cheat the skill with modified equipment is BS. All that being said, I am by no means the end all be all of diving. I am striving to constantly improve though, including my SMB deployment, which I got to put to the test during my recent rebreather training.

 

[DevonDiver]

Guys... (and girls)... I didn't interpret the OP's question to indicate they had a problem deploying a DSMB. They wanted to retain neutral buoyancy on deployment (lungs to bag, then release). The use of a large bag, requiring several exhalations for sufficient gas from a predicted shallow depth on the up-coming training course, would prevent that optimal deployment. Hence the inquiry about shortening the bag....

...or am I missing something?

The answer... is to use a bag that can be inflated from shallow... a smaller bag. The option to modify an existing, larger, bag being generally discouraged for a tech diving perspective (right tool for the job / murphy's law)