Deco diving: Thoughts on whether you like to send up DSMB at, say, 75 ft then gas switch at 70 ft; do your gas switch first then send up the DSMB; or does your choice of when to shoot the DSMB depend on the conditions? Or maybe your instructor/training agency?
Shooting DSMB before or after gas switch at 70' on lake/ocean deco
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PfcAJ
Contributor
I might even send it up on the bottom.
But if I wanted to send it up I'd probably do it before the switch. Provides a depth reference and if there's any buoyancy shenanigans you aren't on the deco gas so it doesn't matter as much.
But if I wanted to send it up I'd probably do it before the switch. Provides a depth reference and if there's any buoyancy shenanigans you aren't on the deco gas so it doesn't matter as much.
Well.... I'm probably an anomaly but I seldom launch a blob in order to create a stable deco depth.
..... uuuuhhhh.... this is probably going to sound arrogant and I really don't want it to... but frankly, I do almost all of my deco "free swimming" in mid-water with no reference.
The way we do this is to divvy up the tasks. My task is normally to control depth and stop times and my buddy normally controls navigation and tempo.
Obviously both divers need to be peripherally aware of ALL tasks (and able to perform all tasks) but this division of tasks allows two divers to perform all tasks with much more precision than either an individual diver, or multiple divers who had no task-divisions, could have.
The last time I launched a blob to create a stable deco platform was during my ADV EANx training. What we did then, and what still seems logical to me today was to launch the blob at the first stop longer than 1 min. That way you have the time and you are not in a "busy" part of the dive.
R..
..... uuuuhhhh.... this is probably going to sound arrogant and I really don't want it to... but frankly, I do almost all of my deco "free swimming" in mid-water with no reference.
The way we do this is to divvy up the tasks. My task is normally to control depth and stop times and my buddy normally controls navigation and tempo.
Obviously both divers need to be peripherally aware of ALL tasks (and able to perform all tasks) but this division of tasks allows two divers to perform all tasks with much more precision than either an individual diver, or multiple divers who had no task-divisions, could have.
The last time I launched a blob to create a stable deco platform was during my ADV EANx training. What we did then, and what still seems logical to me today was to launch the blob at the first stop longer than 1 min. That way you have the time and you are not in a "busy" part of the dive.
R..
I think it all depends upon the situation of the dive. One key factor is why you are shooting it. If it is so a boat can trail you, you want that sucker up on the surface as soon as you start to drift. If that is not a factor, then you would also consider the length of the planned deco stops. If you really want to get onto your 70 foot gas and will be on that stop for only a minute or two, then maybe the bag can wait.
Now that you mention it, John, I have launched blobs from the bottom on several occasions. One such occasion was while diving a wreck in Canada. I knew the dive boat was expecting us to surface along the buoy line (there was a permanent buoy on the wreck) but I got separated from the wreck due to currents I wasn't expecting. Once I lost contact with the wreck I immediately launched a blob (from 33-35 metres) and made my ascent. I surfaced a considerable distance behind the dive boat but they signaled to me that they had seen me (only time I've ever seen the "big OK" sign used with purpose) and after everyone else was recovered they came and got me.
Another time I used a blob a lot was in Egypt. Literally nothing about diving scares me except propellers. I launched a blob (from 5 or 6 metres) at the end of every single dive when we expected to be picked up by a Zodiac because getting run over by a Zodiac seemed like a bad thing and I wanted to avoid it if possible.
So far, so good (knock on wood)
R..
Another time I used a blob a lot was in Egypt. Literally nothing about diving scares me except propellers. I launched a blob (from 5 or 6 metres) at the end of every single dive when we expected to be picked up by a Zodiac because getting run over by a Zodiac seemed like a bad thing and I wanted to avoid it if possible.
So far, so good (knock on wood)
R..
The bloke driving the boat is who matters. If he wants it sent from the bottom, send it from the bottom. Here he (or she) may have 10 bags to watch for a long time. If they start out spread out away from the wreck then the chances of missing one are greater.
I think the nail has been hit on the head.
You generally use DSMB's so that the surface cover knows where you are. During the dive they know you are on the wreck. Once you start the ascent then (if diving tidal waters) you can drift a considerable distance. So generally the boat will want you either to ascend the shot line (fixed point of reference), or deploy a DSMB before leaving the wreck, so that the boat can track the drifting divers.
You generally use DSMB's so that the surface cover knows where you are. During the dive they know you are on the wreck. Once you start the ascent then (if diving tidal waters) you can drift a considerable distance. So generally the boat will want you either to ascend the shot line (fixed point of reference), or deploy a DSMB before leaving the wreck, so that the boat can track the drifting divers.
If I'm launching an SMB, I like to do so at least 10' below a physiological ceiling to buy some leeway in the event something gets cocked up.
ajduplessis
Contributor
Deploy from the bottom.
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