Reducing the length of my DSMB

[PfcAJ]

Learn to use your gear properly.

In any case, if you shorten it, it's going to stick out of the water the exact same amount as if you hadn't. The difference is that you can call it "full", even though it really isn't.

Bottom line one is that taking a shortcut isn't doing yourself any favors.

 

[raftingtigger]

Modification has been rejected.

For all you posters out there that have given me ideas on how to deploy the DSMB - I have tried and found issues with all of them before I posted my question. Not that they aren't good ideas, just that I don't like the way they work for me. I have found the method described in the initial post to be my preferred method, and just was looking for input on the feasibility of making what I already own - and generally like - work for a specific situation.

So far no one has giving me a good reason why the idea won't work, except maybe that the rubber bands will fail. In that case it is no worse than sending up the unmodified buoy partially full. Universally there is resistance to the idea - so I am rejecting making the temp modification for the class since it is quite likely the instructor will feel the same way.

 

[DevonDiver]

So far no one has giving me a good reason why the idea won't work..

When your Tec40 instructor introduces you to an appropriate level of task loading on your course, you will understand some of the feedback given thus far...

K.I.S.S. becomes very important when you feel like your brain is melting

 

[raftingtigger]

K.I.S.S. becomes very important when you feel like your brain is melting

Which is EXACTLY why I want to keep the DSMB deployment as simple as possible. And EXACTLY why I have found the method described in my initial post to be the simplest and most effective method FOR ME.

Everyone is "preaching to the choir", and virtually no one answered my original question - although it is abundantly clear that no one so far likes the idea. As a result I will be using a closed-end, OPV equipped, 2 breath DSMB for the class (with independent practice before hand). After using the new DSMB, I will then decide which to carry with me on which dives.

 

[DevonDiver]

Which is EXACTLY why I want to keep the DSMB deployment as simple as possible.

A simple question then: Do your modifications increase, decrease or retain the exact same risk of complication or failure compared to the intended 'clean' design of the DSMB?

 

[raftingtigger]

A simple question then: Do your modifications increase, decrease or retain the exact same risk of complication or failure compared to the intended 'clean' design of the DSMB?

Good question.

Without testing it in the pool (which I was going to do), it would have simplified the deployment and kept the risk of failure/complication the same - which is why I was thinking about doing it.

 

[DevonDiver]

Good question.

Without testing it in the pool (which I was going to do), it would have reduced the risk of complication - which is why I was thinking about doing it.

Reduced risk of complication assuming everything goes right. What if something goes wrong? Are there failure issues? What's the worst case scenario? How does that match with the task-loading you'll be under when conducting a technical/deco ascent? What if you're also dealing with other distractions/emergencies?

Testing once or twice isn't satisfactory for technical diving. A protocol/approach needs to be confirmed reliable.

 

[raftingtigger]

Reduced risk of complication assuming everything goes right. What if something goes wrong? Are there failure issues? What's the worst case scenario? How does that match with the task-loading you'll be under when conducting a technical/deco ascent? What if you're also dealing with other distractions/emergencies?

Testing once or twice isn't satisfactory for technical diving. A protocol/approach needs to be confirmed reliable.

Devon, thanks, you are actually asking good questions and addressing my question.

First, the only failure mode I can envision is the DSMB reverting to the unmodified form. If rubber bands come off on ascent then the bag might have less air in it at the surface depending on the depth it was deployed and the depth the rubber bands came off. The rejected modification was simply rolling up the top end of the buoy and using rubber bands to keep it from unrolling. No structural changes were made.

Second, you have a very good point about the testing needed. The more technical/complicated the dive, and the more critical the piece of equipment => more testing required.

Lastly, FWIW, I am not planning on actually doing technical dives in the foreseeable future. I am taking the class to evaluate and improve my overall recreational skills. This class was the one that was available in my area, at a time I could take it, for an affordable (to me) price.

 

[OkByMe]

Ok.... Addressing the suggested modification. With the top of the SMB rolled down and effectively trapped so that it does not unroll, it will be top heavy from the excess material. Since it will probably be under inflated too using your method, it will break and lay down at the water line. If you ride the SMB to get it up, which is hard to do at the surface or put more air in it, Which is also hard to do at the surface, it will likely roll out of the entrapment and be under inflated again.

Addressing the method of deployment. There are only 3 ways I can think of to effectively deploy the SMB. One is at a great depth with a breath of air... Probably in the range of 70-80 feet, but that would only about triple the volume you put into it and for a 5 ft. SMB, that is about half of what it needs to be tight. What do you do on the 40' reef dives with boats wizzing over your head?

The other one is my method, and the other is the same except fighting the line to keep it short and untangled. Both of those methods require a pressurized air source.

I guess with a harness to hold a tank you could use a snorkel vest as a BC... I remember the old "horse collar" days, but ultimately the most effective method is just that, anything else is just - not. Effective equipment and the methods to use it is a skill to be learned and will serve you well in almost all conditions

 

[raftingtigger]

Ok.... Addressing the suggested modification. With the top of the SMB rolled down and effectively trapped so that it does not unroll, it will be top heavy from the excess material.

Top heavy is a concern. For grins and giggles I will see if it is, but don't think it will be too top heavy.

Since it will probably be under inflated too using your method, it will break and lay down at the water line.

IMHO any vertical tube type float will flop over at the water line unless it has enough downward force to keep it upright. The biggest difference between a tight float and an partially inflated one should be the height above the water (all other factors being equial)

If you ride the SMB to get it up, which is hard to do at the surface or put more air in it, Which is also hard to do at the surface, it will likely roll out of the entrapment and be under inflated again.

I have never found it hard to add air to a DSMB at the surface. They are designed to be easy to do this. You do need to use the oral inflater rather than the regulator. As for rolling out of the entrapment, unlikely since I inflated the buoy with my LP inflater and had the OPV release without any change in the rolled part. Even if it did roll out of the entrapment all that it needs is a little more air, which at the surface is a trivial issue.

Addressing the method of deployment. There are only 3 ways I can think of to effectively deploy the SMB. One is at a great depth with a breath of air... Probably in the range of 70-80 feet, but that would only about triple the volume you put into it and for a 5 ft. SMB, that is about half of what it needs to be tight. What do you do on the 40' reef dives with boats wizzing over your head?

As in my original post; the 5.5' DSMB takes 3 full breaths for me. At <66 FSW it will be FULL at the surface. Double check your math. As for the 40' reef dives with boats whizzing by overhead? I don't have that kind of diving environment. My buddies keep looking at my funny when I send up the DSMB from our 15' safety stop for practice.

The other one is my method, and the other is the same except fighting the line to keep it short and untangled. Both of those methods require a pressurized air source.

Not a method I really want to try with all the kelp I deal with. For me, the less dangly lines the better. I did read about the method before and can see where it could work well at times. Not dissing the method, just not going to use it.

I guess with a harness to hold a tank you could use a snorkel vest as a BC... I remember the old "horse collar" days...

I'm a consumate DIYer, but that is going a bit too far .