Making a practice DSMB - how?

[ardhill]

Somewhere alone the line I have read of someone using an old SMB and making it into a practice one.

I guess this means making some sort of extra hole in it so that once on the surface, the air comes out and you get your SMB back down to play with again.

I want to be able to actually shoot the thing up to the surface, so need to make it small enough to be able to inflate it. And I need it to deflate so it will come back down. So, how big a hole do I make and where?

At the top, middle, bottom... where?

At the top so all the air can escape? At the bottom so it falls over and the air escapes?

Anybody made one?

[ratcliffe]

I think that if you put the hole near the top of the blob, ie the furthest point from where it is attached to the line, then once it has gone up (assuming you can fill it faster than it deflates), it will go to the surface and let some air out, then you can gently pull it back down by reeling in (being careful not to rise yourself instead of pulling it down), and as you reel in, it will pull the blob upright on the surface and downwards, and the top point will vent the air.

How does that sound ?

[Richard Mason]

Originally Posted by ratcliffe

I think that if you put the hole near the top of the blob, ie the furthest point from where it is attached to the line, then once it has gone up (assuming you can fill it faster than it deflates), it will go to the surface and let some air out, then you can gently pull it back down by reeling in (being careful not to rise yourself instead of pulling it down), and as you reel in, it will pull the blob upright on the surface and downwards, and the top point will vent the air.

How does that sound ?

I reckon it would - we have a similar set-up (in principle) here, with first flush diverters for discarding the first few gallons of rainwater off a roof, so that all the birdsh!t and dirt gets diverted to waste when the rain first starts, ensuring you don't have a slug of dirty water going straight into your rainwater tanks, which are used for drinking water supply in remote areas.

It would just have to be a very small hole - I'd start with something maybe pencil-sized in diameter.

Just make sure you write "PRACTICE" on it and maybe have it shaded a different colour so you don't accidentally take it away on some screamer of a drift dive, where you really need a DSMB.

[Janos]

One word of advice - make the hole really, really, really small. You can open it up later if needs be.

Janos

[ardhill]

Originally Posted by Janos

One word of advice - make the hole really, really, really small. You can open it up later if needs be.

How small is that? Pencil sized like suggested above? Pin hole has got to be too small hasn't it?

How about I clip a top corner would that be the right place?

BTW, it's one of the open ended types. I thought that they are so useless* that I would fall over at the surface anyway. But of course when I tried it, I was so shallow (as it was only for practice) that it didn't completely fill up, so didn't fall over and empty.



[* For those of you who successfully use open ended SMBs, I do give the probable option that it in fact me who is useless using it]

[andrallan]

What I do is to use a simple open ended DSMB and put an eyelet in the top. I attach a length of cave line to the eyelet and attach the other end to a 2kg weight which I place about 2m from the release point of the DSMB. (Coil the line neatly!)
Simply pulling on this line inverts the SMB and down it comes! (You can even use a line 2m less than the depth you are at that way the SMB never breaks surface.
I goes without saying that you place the "class"well away from the tethering line to avoid entanglement)

[Woz]

I wouldn't bother with any of this. I'd just get an empty 4 pint plastic milk carton with a handle and fire that up and down until you are bored.

[ardhill]

Originally Posted by andrallan

What I do is to use a simple open ended DSMB and put an eyelet in the top. I attach a length of cave line to the eyelet and attach the other end to a 2kg weight which I place about 2m from the release point of the DSMB. (Coil the line neatly!)
Simply pulling on this line inverts the SMB and down it comes! (You can even use a line 2m less than the depth you are at that way the SMB never breaks surface.
I goes without saying that you place the "class"well away from the tethering line to avoid entanglement)

So, do you have a line for the top and a line attached to your reel? Then you also need to hold a 2Kg weight as well?

I think the way it works in my mind must be different from the way you actually do it, as it looks like you need four hands to deploy safely. Never mind the class staying away from entanglement, what about the person deploying it?

I think I don't quite have a correct picture of what you are doing.

I am talking about using it for a single person deploying in mid water.

[ardhill]

Originally Posted by Woz

I wouldn't bother with any of this. I'd just get an empty 4 pint plastic milk carton with a handle and fire that up and down until you are bored.

Do you attach that to a reel Woz?

[Woz]

Originally Posted by ardhill

Do you attach that to a reel Woz?

Uh huh. Fire it up, pull it down, empty. Fire it up, pull it down, empty.

If you can fire a milk carton a DSMB is a doddle. Although you do get strange looks as you jump in with a couple of Co-op's finest strung round your waist.