SMB Depth Questions

[Belzelbub]

Why would you try to slow (or break) the ascending smb? What benefit does that provide. Seems like it might increase the chance of fouling the reel as the line is screaming out?

I don’t use a reel with my DSMB, but this reminded me of learning to fish with a bait caster reel. When casting, you want to apply light pressure on the reel to prevent fouling. Principle sounds essentially the same. When the line is spooling out, the reel itself is spinning quite fast. At some point, the far end of the line (DSMB or bait) will stop and the line will go slack. The spool itself still has momentum, so continues spinning. The slack line gets tangled up in a rat’s nest of line.

Given the fine line and less dense environment, it’s probably more of a problem with a baitcaster, but similar idea. Brake is to keep the line taut. Taut line is unlikely to foul.

 

[MacDuyver]

. Also, most people are launching from much shallower and need more air in them to be rigid at the surface.

*mandatory joke about nobody liking floppy sausages*

 

[Wibble]

Why would you try to slow (or break) the ascending smb? What benefit does that provide. Seems like it might increase the chance of fouling the reel as the line is screaming out?

It's to check that it's still going up and to ensure everything's tight and the bag isn't going sideways. When using a spool, just squeeze a bit on it.

I use a very strong Kent Tooling reel which works well for this.

Also, if you are deep on a wreck, why would you put as much air as possible into the smb before release? I try to put the minimum amount of air in the smb, just enough to have it about full when it gets to the surface. It seems far less dangerous to have a slightly filled smb on the bottom (should it get fouled or tangled) versus one that has been filled "as much as possible".

Because it's an embarrassment to have a flaccid blob when you get back on the boat. You want one that's properly inflated that you can be proud of.

I've found that even at 50m/265ft, the full-size Halcyon Super Big 1.8m/6ft SMB needs a good injection of wind to make it stiff (Lift capacity 23.6kg, so 25 litres of wind at least). Giving it the beans and injecting longer ensures I have the stiff one and impress everyone on the boat

More realistically, a fully inflated SMB can be waved around if the boat's a way off, it gives you more lift should you need it, it maximises the size of the SMB, etc...

When inflating, it'll unfurl in front of you and be out of the way as you're pushing in that little extra wind.

If inflating it shallower, say 18m/60ft, then you really do need to keep injecting as much as you can, even finning downwards against the buoyancy.

But hey, I've got the big one so everyone can see it.

There's no point in a itty bitty SMB unless you're training in a lake.

 

[Wibble]

I have several spools with 55+ m of line. I have never been in a situation where I need a reel (100+ m of line) to shoot a DSMB.

OK.

We regularly throw up a bag from the wreck which could be 60m/200ft deep. When you've finished your dive there will be current running, possibly 1 or 2 knots. Also you may be sheltered on the wreck from the current and the wreck may change the direction of the current too.

I've seen a bag go up sideways from a wreck when released!

The additional line on a 100m/330ft reel takes that into account and has spare just in case you've sent it up even deeper.

There's practically sod all difference in a reel with 60m and one with 100m. So I dive with 100m of line knowing it'll work pretty much everywhere.


I did catch a lobster pot line once where strange things happened to my buoyancy before I looked up and worked out what had happened. Letting out some more line took the strain off and allowed me to swim to get around the line. OK, didn't need 100m...

Oh and the scared the bejesus out of me moment... Floating at deco into a lobster line; it ran up the inside of my leg to my crotch and the Chimp Brain thought it was Jaws!

 

[steinbil]

Technically, you only really need the extra scope when there is variability in the velocity of the current in the water column. In other words, if the current is uniform the bag will go straight up and only be affected by wind when it gets to the surface.

Does this not assume that the bag has the same amount of drag as the diver?

I would think that the SMB would more easily be pushed by the current and flow with the water than a streamlined diver in trim. My own experiences of shooting a bag in current would say the SMB is almost always pulled sideways faster than myself, and the line ends up being diagonal in the water. I'm not 100% sure how much of this is caused by variability of velocity of current at depths vs difference in drag.

 

[Wibble]

Does this not assume that the bag has the same amount of drag as the diver?

I would think that the SMB would more easily be pushed by the current and flow with the water than a streamlined diver in trim. My own experiences of shooting a bag in current would say the SMB is almost always pulled sideways faster than myself, and the line ends up being diagonal in the water. I'm not 100% sure how much of this is caused by variability of velocity of current at depths vs difference in drag.

There's probably the "rocket" affect of the bag too. If it goes sideways for a bit, it'll continue sideways?

 

[johndiver999]

Does this not assume that the bag has the same amount of drag as the diver?

I would think that the SMB would more easily be pushed by the current and flow with the water than a streamlined diver in trim. My own experiences of shooting a bag in current would say the SMB is almost always pulled sideways faster than myself, and the line ends up being diagonal in the water. I'm not 100% sure how much of this is caused by variability of velocity of current at depths vs difference in drag.

No, you are mistaken. Where I dive the bottom can be stopped and the top is moving 4 kts. That causes the bag to pull the diver horizontally in the (slower) water column and also vertically upward, sometimes with a good bit of force.

 

[MrChen]

You can shoot that bag from any depth as it has a relief valve. The deeper you are, the less air you need to put in it due to the expansion of the air as it ascends. But you do need to make sure you have enough line! Much below 20-25 meters you will want a reel, not a spool. You need to account for the current as the bag will not go straight up but rather it will ascend at an angle. You probably want at least 50% more line than your depth, but that is a guess. Others may have a more precise calculation.

Sometimes I look up and my DSMB is shooting through the water column horizontally on it's way to the surface.

 

[MrChen]

I like to "cheat" when shooting my DSMB. I always carry a slung pony bottle because I am typically diving solo. Almost all of my diving is drift diving in SE Florida, so I have to shoot a DSMB quite a bit. I have a short BC hose on my pony, around 15-18", and use that to inflate the DSMB. I keep it tucked under the hose retainers on my pony and just pull it out when needed. I like to deploy from depth before my ascent, typically from 60-80'. A short burst of air from my pony and the DSMB is rock solid on the surface every time. I then re-tuck the inflation hose and begin my ascent.

I rigged my pony the same way after seeing Divin'Papaw launch a DSMB in seconds. When back mounting my pony, I added an additional hose to my primary regulator so that I can do the same thing using my main tank.