safety with counter-weight system

[reidfish]

Hi All,
I have built a counter-weight diver retrieval system for diving in our local lake, which has deep water but low visibility and quite dark at depth. We are still testing weight combinations etc, but all is operational and seems to be a fairly safe setup that gives me confidence I will not be lost or left at the bottom of the rope if I black out at depth. We are using 1m long lanyards which are working fine.

My question is, "How many safety scuba divers, if any, should we be using with this system, according to 'best practise'?"

Thanks in advance

 

[efattah]

Using a counterweight system without scuba divers is generally referred to as a 'blind' counterweight or blind counterbalance.

When using a blind counterbalance system, the retrieval time is proportional to the target depth of the athlete. In the standard case, the bottom weight is at the target, and when the athlete does not emerge after the target dive time, the system is activated, dragging up the diver.

Assuming that the diver swims at 0.9m/s, and that the system retrieves the diver at 0.7m/s, take the example of a 60m dive:

Target depth: 60m
Target dive time: 120m/0.9 = 133 seconds
Assume diver ruptures ear drum at 45m and blacks out from vertigo at 50m (i.e. 50/0.9 = 56 seconds into dive).
Diver fails to surface.
Counterbalance system activated at 133 seconds.
Diver arrives at surface 86 seconds after system activated.
Diver arrives at surface at 133+86 = 219 seconds after dive began.
Diver blacked out at 56 seconds into dive, so diver has been unconscious for 219-56 = 163 seconds = 2'43".

The standard rule is that once a diver blacks out, the laryngospasm lasts for about 2 minutes. If the diver is still underwater, more than 2 minutes after blacking out, he will likely get water into his lungs. If he is unconscious underwater for more than 3 minutes, he will almost certainly get water into his lungs. It a cold lake, water in the lungs will mean instantaneous severe hypothermic coma.

So, with a blind counterbalance, in a lake, on a 60m target, chances are you'll be retrieving a diver who has been 'out' for nearly 3 minutes, with water in his lungs, in hypothermic coma. Chances for revival will be slim at best, even with paramedics, a platform and defibrillators. For dives of 70m, 80m or more, blind counterbalance devices are (in my opinion) corpse recovery devices.

Using even one scuba diver at the half way or three quarter point will DRAMATICALLY increase the success of the system. Typically, the scuba diver is equipped with an airbag to lift the entire line up, another air bag to lift the diver up, and a signalling device to signal the surface to activate the counterbalance.

Alternatively, you could build an in-the-water DRUMS system like the GoldenAngel system we are using here (which doesn't require scuba divers). (see related thread)


Eric Fattah
BC, Canada

 

[Silver]

Eric, what if you use some kind of a signal at target depht ? Perhaps an audio signal? You would cut the time for activating the counterbalance system in half...And you would avoid puting any scuba divers at risk !

Magne

 

[reidfish]

Wow, thanks for the feedback Eric. You da' man!
I will do some tests on time and speed etc. Maybe having the release at -10m would also save say 20 seconds? My main concern is that I am protected at the relatively shallow depths that I dive to (with a target of -40m this year). And also to help my buddy Ants train for his -60m (might be doing lots of 50's). It may be that we test the system, do the calc's, and cut the rope at that depth so it can't be used any deeper.

Using my typical dive profile, about 1m/s and a retrieval speed of 0.75m/s (yet to be confirmed by testing), a blackout at the bottom plate on a -40m dive would give me 40 s before the system is activated, and 53 s travel time, giving a post-SWB time of 93 seconds. A 50 m dive would leade to a dive time of 116s (too close).

Of course a diver blacking out on the way back up at -20m would take less time to notice he was overdue, but retrieval time is the same as they wait there until the bottom plate hooks the lanyard. The 40m rope would take 73 seconds post-blackout, and the 50m dive 86 s.

 

[Skindiver]

Just how good are fish-finders for monitoring freedivers progress up and down the line?
Would the image be clear enough to distinguish the diver from other small sea life / dam life or even the rope ?
Is the units tracking ability delayed or staggered ? Would the diver track smoothly down and up the screen and if there is an interruption in diving progress would an operator be able to see it clearly enough to activate a recovery winch effectively ?

I have considered fitting out a boat with a winch ( anchor winch ? ) that reels in line fast, and monitoring the diver with the fish-finder. The diver uses a lanyard and is winched up with the line if the operator sees an interruption in his progress. Also an electronic shark ( pod) retardent is set up at the line to allow carefree breathe-ups in SA waters.

skin.

 

[flyboy748]

Someday I'll have a boat based DRUMS system like you're suggesting Skindiver. However I need a boat first! The electric drums system however will be activated as soon as the pull on the line is felt by the operator, or at the set time if there is no pull... Then it will pull the line in at 0.7 - 0.9 m/sec. (just a little slower than the diver) depending on the divers normal acent speed. That way the dive time will be within seconds of planned, wether the diver blacks out or not.

In the meantime I'm going to use the counter-weight system to 30m. No deeper for now without Scuba safety. I think the FHOF system is great whenever scuba safety is used as well. It's reusable, fast and fairly cheap. I'm hoping to be able to get one for our club here in Toronto.

Aaron

 

[Jon]

Getting ready to put mine together and wondering what kind of pully blocks to get.

I am running 5/8" line and am not sure which ones to go with. I've looked at the sailing websites and there are a dizzing array of choices.

Just wondering what others are using and what kind of prices they found.

BTW: I checked out the rock climbing figure-8's and they won't work because of built in friction ridges that would slow the whole process down too much.

Thanks!

Jon

 

[Longfins]

Jon,


I use climbing pulley from REI (CMI Original 101), around 25$. Probably won't last forever, but it's cheap. I have 3/8-7/16" dia ropes. It should probably fit your 5/8 as well.

Peter S.