Questions about SMB

[Fastmarc]

Hi.
I recently purchased a DAN smb and I am getting around to trying it out and getting some practice, but I have a few questions that I was hoping to get help with.

When you inflate one of these below surface, how do you know how much air to put in?
Also, because I was curious, I inflated it on land and found that though air can be added to it through the bottom (as well as a lp inflator), the thing just fills up until it is hard. It somehow prevent the air from escaping back through the bottom.
Will this burst if it over inflated at depth for the decrease in pressure on the way up?
It does have a dump valve with a string attached.

 

[The Horn]

add enough air so it will rise from depth. As the air will expand as the SMB rises the dump valve should blow off to prevent bursting

 

[Diver Dennis]

It depends how deep you are. If you are doing your normal safety stop, I fill mine about 3/4 full. Make sure you practice. It takes some skill not to get wrapped up in the line from the spool and to maintain depth when filling it.

 

[do it easy]

Hi.
When you inflate one of these below surface, how do you know how much air to put in?

Use Boyle's law- at 33', the air you put in at depth will expand to twice the volume by the time it hits the surface. at 66', it will be three times the volume, and so on... you don't need an underwater calculator, just get close and if it is under-inflated, pulling down on the line will make the marker stand up.

 

[Fastmarc]

Thanks guys.
I filled it with air and when I squeezed it to increase the pressure, the dump valve did give way and let off some air.
I need to get some practise with it.

 

[Mantaman]

A word of caution like was mentioned above......practise!!!! A DM in Malaysia last year was inflating his SMB and the string wrapped around his fins. When he filled it and relaesed it, the SMB drug him to the surface and into the prop of a dive boat. Luckily his injuries were not severe but he did get cut up. Weight the end of the string and make sure you are clear before you fill it. Also, one shot of air and then let go so theSMB does not pull you to the surface.

 

[spectrum]

The fill volume wants to be as do it easy described. You need to balance that against your ability to hold it down while it fills while making certain you don't get entangled. Practice is important.

pete

 

[Fastmarc]

I came across this video and was planning to use it as a guide.
http://www.thumpershole.com/images/DIRF Training Videos/shootbag[1].m1v

 

[spectrum]

That's the idea. Practice first in a modest depth, like 20 feet and work your way out. Having a buddy add the air with their alternate 2nd stage can cut down on the task loading.

Be sure you become proficient at doing it solo. To date my only real use has been when a buddy vanished and I had to surface in potential boating traffic. It worked out well.

Pete

 

[BarryNL]

Thanks guys.
I filled it with air and when I squeezed it to increase the pressure, the dump valve did give way and let off some air.
I need to get some practise with it.

Yep - practice lots. DSMBs are one of the most difficult skills and the big danger is getting dragged to the surface by them. It goes without saying that you never clip the reel to you once you've started the deployment process - this includes once the thing is up as it can always get caught by a boat and drag you.