Report Number: 103

Reported By: JeffB

Report Date: 11/4/2002

Location: The Hinkel Experiment

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Last Saturday two buddies and I decided to do an experiment. At the suggestion of the most experienced diver (a cave instructor) we proceeded to do a scooter dive back to the Hinkel. This was a place we had all been to before. The plan was for myself and my buddy to breathe our stages to Hill 400, drop them off, switch to back gas and then scooter the remaining way to the Hinkel. The experienced diver carried a spare full AL80 stage for contingency. At no point did I feel we put ourselves in jeopardy any more than usual :).

We wanted to get some realistic data on how careless scooter dive planning can get you into trouble. The Hinkel restriction is 3,000 feet back in Ginnie Springs and normally one would not breathe 1/3rd of a stage, drop it, and then continue on breathing down 1/3rd of backgas while scootering. It's just too risky, as our data shows, since you are depending on having a scooter to haul you all the way back and if it fails you are now looking at a Long Swim instead. On my typical DPV dives my buddies and I breathe only stages and leave the backgas "for emergency use only". A high flow cave such as Ginnie might lead one to get lazy with dive planning and assume you can just ride the current out in case of an emergency.

We chose to combine three different types of "disaster scenarios" into the mix at different points during the exit of the dive so we can do more than one experiment during the dive. After scootering to the Hinkel we did the following:

I recorded the remaining pressures in my stage and backgas, as well as penetration distance and time so we would have raw data. The spreadsheet below has all of the raw data, if you are interested. I then projected some "worst case" emergency scenarios that assumed we had to handle the emergency from the point of maximum penetration (3,000 feet) until we reached the stage bottle at 500 feet. We only "survived" one scenario:

Sharing air, riding separate scooters - survived
Sharing air, swimming out two dead scooters - "died" 1,200 feet in on the mainline, 700 feet from the stage bottles
Lights out, swimming out without sharing air - "died" 2,040 feet in
Lights out, swimming and air sharing - "died" 2,740 feet in
Obviously there are pros and cons here, but the point of the experiment is valid and illustrative. This is like that "pie piece" analogy some use (including me) before and during a dive. If a piece of gear fails, take away a piece of an imaginary pie. When three pieces have been removed, it's time to either not do the dive or call it. The chances of two scooters failing is somewhat remote, but the chance of two divers "overdiving" their battery time is not unlikely, given human nature and the tendency for some to be more aggressive as they get complacent and comfortable at greater distances. Air sharing is not out of the question, but the probability is lower when you tack on two scooters failing. The final two scenarios, with loss of six lights, two scooters (with no light they are, in effect, dead) and one person's air is stretching it. Still, I find it fascinating to play these "what if" scenarios and hope it makes you a smarter, safer diver.

Dive 1 Hinkel                        
Location Devil's Ear  
Date 11/2/02   MaxDepth 95
Time 12:40 PM   ATA 3.88
Mix 34%/66%   ft3/100 PSI 2.7 (AL 80 stage) ft3/100 PSI 7.2 (twin 95s backgas)
 
Time Backgas Backgas Backgas Stage Stage Stage Total
(mins) Distance PSI PSI Δ ft3 left PSI PSI Δ ft3 left ft3 Used SAC rate Event      
0 0 3615 0 260.3 3100 0 83.7 0.0 0 Start of dive at Devil's Ear  
10 500 3550 65 255.6 2200 900 59.4 29.0 0.75 Dropped stage; switched to backgas
34 3000 2450 1100 176.4 2200 0 59.4 79.2 0.85 Hinkel; turned; 100 feet touch contact
39 2900 2200 250 158.4 2200 0 59.4 18.0 0.93 Begin swimming air share, lights on
52 2000 1100 1100 79.2 2200 0 59.4 79.2 1.57 Still sharing, switch to DPVs  
62 500 450 650 32.4 2200 0 59.4 46.8 1.21 Stop sharing, go on retrieved stages
69 0 450 0 32.4 1500 700 40.5 18.9 0.70 End of dive    
Projected "worse case" scenarios (assuming travel from 2,900 feet to the stage at 500 feet; a total of 2,400 feet)
Est. Avail Dist
Time Est. Gas Using Dist "Bodies"
To Req Avail Leftover Time Avail From Found
Scenario Ft/min SAC Stage Gas Gas Gas Left Gas Stage At
DPV, share 150 1.21 16 74.9 158.4 83.5 34 5077 -2677 Survived!
Swim, share 69 1.57 35 211.2 158.4 -52.8 26 1800 600 1200
Dark 20 0.85 120 396.0 158.4 -237.6 48 960 1440 2040
Dark, share 20 1.57 120 731.1 79.2 -651.9 13 260 2140 2740

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