yeah - Rich told me about how the only thing more disturbing than having his mouthpiece come off his reg (leaving him breathing water) was how funny you found it!!Originally Posted by EGIB
Yes, yes, yes. I am 100% with Richard.
It often worries me how frequently we replace careful thought with "rules of thumb". I think that swimming to the Henkle is damn good practice, and I recommend it to anyone who is serious about cave diving. But it does little to improve your scootering skills.
To survive a scooter death/flood, you need to have careful gas planning, or a buddy who you are comfortable won't lose you and disappear into the cave after your scooter dies. Preferably both. This means, once more, understanding that thirds is not a solution.
Frankly I think that the way this is taught is pretty poor. For any serious penetration, I recommend that you sit down with Excel and do some serious "what if" planning. A hint - using a scooter, in some ways, turns a cave into a syphon if you work on the assumption that it works on the way in and fails at the worst point. Hence, once you have estimates of your swim speed, the scooter's speed and the flow rate in the cave you're diving, you can use the spreadsheet that I posted around Christmas to plan safely. Enter "Speed" as your swim speed, plus (scooter-swim)/2, not the scooter speed, and add (scooter-swim)/2 to the flow rate as well. Flow rate should be entered in the sheet as negative in a spring like Ginnie, or positive in a syphon.. For example, let's say you're scootering Ginnie - and that your swim speed is 50 fpm, your scooter speed is 100 fpm and the flow rate is 20 fpm (all these are made up as I think it's important for each person to verify their own speeds). Then enter "speed" as 50+ (100-50)/2 or 75 and "flow" as -20+(100-50)/2 or + 5 as the flow rate. See - your scooter has just turned Ginnie into a syphon! How scary is that? Allowing for a bare exit, and allowing for the possibility that you will have an OOA AND a scooter failure on one dive (remember, scooters fail often - did you REALLY finish charging it last night?), you should turn at a rounded pressure of 2600 PSI in tanks at 3600 PSI. That's actually not too bad. Thirds would not cut it, sixths is too conservative. I'd probably plan a turn at 2800 on this dive.
Once more - swimming with a scooter is equivalent to INCREASING your swim speed by (sscooter-swim)/2, and INCREASING the flow (where a syphon is positive, a spring negative) by the same amount. To get some intuition of why this is true, add in the numbers for a situation where your scooter runs at exactly the same speed as the flow in that cave and see what happens.
The link for my spreadsheet is at http://www.andrewainslie.com/spreads...s%20Murphy.xls - and I am not going to explain my algebra for why you should add (scooter-swim)/2 to both the flow rate and the swim speed as I'd like someone independent (hey Doron, are you there?) to once more verify my math.
Seriously, if you want to do big dives solo with a scooter, you need to do some spreadsheet work, and to have reasonable measures of your swim, scooter and flow speeds in the cave you're penetrating. This stuff is too serious to be using silly rules of thumb that don't work.
Or what the hell. Swim it, and use that overconfidence to think you're OK now.
Frankly I'm done with swimming. I'll happily go do Manatee waaaaay past where I could ever swim... when I find someone to do it with
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