Gas Blob error

[John63]

Need to know the volume of the SMB to do this as it is dependant upon the volume of gas required

but if you have a 10 litre DSMB and a 0.1 mini cylinder on a self inflating dsmb, it would need 100 bar to be full at the surface (half full at 10m)

15 litre bag = 150 bar required

20 litre bag = 200 bar.


If you had the buddy dsmb with the 0.2 litre cylinder then you would need half the pressure

1 litre bag = 50 bar required

15 litre bag = 75 bar required

20 litre bag = 100 bar.



Cheers, John

[neilh]

Originally Posted by The_blue

Would someone with a little spare time fancy working out what the minimum bar pressure would be to inflate a blob at say 10 meters?

Fully inflate at 10M or inflate enough at 10M for it to be full at the surface?

Originally Posted by John63

Need to know the volume of the SMB to do this as it is dependant upon the volume of gas required

As John says you need to know the SMB volume and, as you asked for a value in bar, you also need to know the size of the supply cylinder.

A quick hunt on t'internet turned up an average SMB (an Agir one) with a lift value of 15Kg. I think I'm right in saying that equates to displacing 15L of water and, whilst not absolutely accurate I think* it's fair to use that as the amount of gas you need for it to be full at the surface.

As John says the volume of gas in the blob is going to double from 10M to the surface, so 7.5L at 10M should give you a full blob at the surface. However if you've got a 0.1L crack bottle, then by my reckoning you're going to need to use 7.5/0.1 = 75bar to get 7.5L in.

If you're using a drysuit hose fed from twin 12s then you'll need 7.5/24 = 0.3 bar

* Though I'm sure the more knowledgeable on YD will be along soon enough

[Eoin]

Could have been worse. I remember a few years back I was coming up after a dive and attached the blob to the reel and then sent the blob up. Only then did I realise I'd attached the blob to the wrong clip on the reel....I'd attached it to the one that you use to clip it to a D ring, instead of the one on the end of the line! End result was my reel and blob on the surface and a sh1t load of line dropping all around me. Luckily the skipper had a sense of humour...

[Gram43]

First time my old buddy sent his crack bottle blob skyward he'd fannied around attaching and unattaching the damn things together so much, when it came time to open the bottle, he did so but fully. The whole lot shot out of his hands and went up like a polaris missile.

When we got to our boat he very gingerly asked the skipper if anyone had picked his blob up and he was pointed in the direction of another diver to ask. Apparently the blob surfaced in between this diver and his buddy and hit the said diver in the face, OOps!

After much grovelling and apologising he got it back. Nowt like practice eh.

[Twinsetmad]

I fired a blob on a delaydaid up from 40m at the Eddistone light house a few years back and watched in horror, as I hadn't attatched it to the reel.

My DSMBi has been great and up to yet, I haven't forgotton to fill it. I also now use screwgate clips on my reel SMB attatchments...