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Oriskany Fatality November 28, 2009

Posted by Chris Sullivan in Emergencies, Shipwrecks.
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I stumbled on this Fox News story today. There aren’t enough details to know anything about the incident, but from my own experience this wreck is a challenging dive, not just because of the size and depth of the wreck, but the two hour boat ride each way can not only be tiring, but puts help a long way away.

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Log problem on Shearwater Pursuit November 23, 2009

Posted by Chris Sullivan in Equipment.
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A very minor problem, but after logging a 2 day dive due to the minor problem reported yesterday, I can’t step through the log (which goes backwards) on the computer to, or past, that “dive”. I hope I’ll fare better with the Shearwater Desktop Software.

Unintentional Altitude Dive November 22, 2009

Posted by Chris Sullivan in Fitness and Nutrition.
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I flew down to Ft. Lauderdale from Toronto on Thursday night (wreck diving in the Keys) and had an interesting problem.

Curious to know what the barometric pressure was in the aircraft cabin (about 790) I turned on my Shearwater Pursuit. I’m pretty sure I turned it off but I’m not totally certain.

The next day, while getting my gear together, I noticed it was not only on, but it showed that I was at a depth of 7 feet. The only way I could turn the computer off was to remove the battery. Fortunately a Canadian dollar coin was available.

New Shearwater Desktop Software November 13, 2009

Posted by Chris Sullivan in Equipment, Technical Diving.
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I just downloaded and installed Version 0.9.9 . I was wondering why it wasn’t released as Version 1, but found out the next day that Version 1 had been released. The first snag I ran into was trying to move the dives from my beta version 0.9.3 to the current version didn’t work.

Reloading worked fine, although dives 1 and 2 are lost as I’d exceeded the maximum of 32. New features appear to be dive export and print. I was disappointed that a double-click on the list of dives doesn’t bring up the details like it did in the beta version. Not sure why that was taken out. You have to go to the menu bar and select “dive graph” to see it.

The Print function is a definite improvement over doing screen grabs like I’ve used in the past for this blog. It puts the graph at the top of the page and the details at the bottom, which I think is a nice layout. I printed one of my dives to PDF for your amusement. One minor nuisance is that you have to save you details before they’ll show up in the print function.

Dive 27

As for the export function I have no real use for it, but it will spit all the data from the log in either csv or xml formats, just in case there’s some useful analysis to perform on it. Here’s a piece of the xml detail.

<diveLogRecord>
<currentTime>3170</currentTime>
<currentDepth>20.6</currentDepth>
<firstStopDepth>20</firstStopDepth>
<ttsMins>20</ttsMins>
<averagePPO2>1.14</averagePPO2>
<fractionO2>0.71</fractionO2>
<fractionHe>0</fractionHe>
<firstStopTime>7</firstStopTime>
<currentNdl>0</currentNdl>
<systemByte>10</systemByte>
<currentCircuitSetting>1</currentCircuitSetting>
<waterTemp>71</waterTemp>
<errorAcks>0</errorAcks>
<errorFlags>0</errorFlags>
</diveLogRecord>

You can see that I’m in mandatory deco (NoDeco=0) and that I’m breathing EAN71 and the water temperature is 71 degrees Fahrenheit. I’m currently on the 20′ stop at an actual depth of 26′. Some of the information here, like the mix, is recorded in the details but not accessible through the program’s user interface. I would have liked the breathing gases to be recorded. The details allow you to enter the breathing gas (presumably the back gas) manually. The software however is quite useful and is also a free download, so I’m willing to wait for all my favourite features.

There’s also a header record that shows about 25 parameters like the start time, start and end battery voltage, and other things.

An odd thing about the dive list is that when I did my download, dives 34 and 35 were at the top of the list, which 3-33 followed them in numerical order. I’m not sure why, but I wonder whether it’s a reflection of how the dives are stored in the computer. However, clicking once on the dive # column header set them up in their proper order, while clicking again puts them in reverse order.

Shearwater Predator Video November 10, 2009

Posted by Chris Sullivan in Equipment, Technical Diving.
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A buddy sent me a pointer to an interview at DEMA 2009 by Curt Bowen from Rebreather World and Advanced Diver Magazine with Bruce Partridge from Shearwater Research about the new Predator Dive computer.

Bubble Compression November 9, 2009

Posted by Chris Sullivan in Technical Diving.
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I saw an interesting slide at the UHMS GLC meeting in October. It compared dive profiles that were virtually identical except for a very deep bounce at the beginning of what was otherwise a “square” profile. The presenter stated that there were less observed bubbles after the dive that began with the bounce than the one that didn’t.

That’s quite astounding. One would think that starting a dive with a bounce would increase the number of bubbles, not decrease it. This result seemed to support some of the claims made by bubble model proponents that neo-Haldanean compression models miss opportunities to exit from deep dives earlier. The effect is explained by the theory of micronuclei, which can be made up of very small bubbles that already exist in the bloodstream, which grow larger in the presence of supersaturated inert gas (i.e. Nitrogen or Helium) and cause problems. The deep bounce crushes these micronuclei to a degree where they do not easily accrete dissolved gases and grow to a size that would cause the diver problems.

Sounds intriguing, but I’m still not convinced that this is safe enough for my personal use. I worry that certain environmental conditions or dive profiles would result in a reversal of the effect and the onset of serious DCS. I’m probably full of “it” on this topic but if one model predicts I’m going to be fine and the other predicts I’m going to be writhing in agony, I’m going to err on the side of staying down a little longer.

Respiratory Minute Volume November 7, 2009

Posted by Chris Sullivan in Technical Diving.
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It’s interesting that there is no agreement among agencies as to the exact definition of Respiratory Minute Volume (RMV) and Surface Air Consumption (SAC).

My original certification agency, NASDS, defined SAC as the surface equivalent number of PSI per minute on a dive, which is (PSI Consumed/Total Dive Time)/((33+Depth)/33).

IANTD does the same thing, and defines RMV as the SAC/(Working Pressure/Rated Cylinder Volume).

DSAT defines SAC as the same as IANTD and NASDS defines RMV, and defines RMV is the (Tidal Volume minus Respiratory dead air space) times breaths/minute. I added the parenthesis to what I read in the book (p42 Tec Deep Diver Manual) because otherwise it doesn’t make any sense. Oddly the Encyclopedia of Recreational Diving doesn’t seem to mention either term. Wikipedia’s definition of RMV is similar to DSAT but doesn’t factor Respiratory Dead Air Space.

In the SDI solo diving course SAC is defined as the volume per minute consumed at rest on the surface. They recommend breathing from a tank while sitting around watching TV or like activity to measure this. For me, consuming about 325 PSI of a 3000 PSI working pressure tank with a rated volume of 77.4 cubic feet in 30 minutes, this was about .28 cubic feet per minute. They call what IANTD and NASDS call RMV the SRMV, or Surface Respiratory Minute Volume. They then go on to recommend that before each dive the RMV by multiplying by the number of absolute atmospheres of pressure and also by a “Dive Factor”, which takes into account effort and should be at least 1.5 for an easy dive, and perhaps more than 3 for a high effort, cold or stressful dive.

Disconcertingly, their sister agency, TDI, recommends determining SAC using a swim at depth, the very thing that SDI says doesn’t work, and implies that RMV is just another term for SAC.

0.28 seems a bit low. I think having the reg in my mouth called attention to my breathing and slowed it down some. At 33 feet a tank would last over 2 hours at that rate, although my record is about an hour and 20 minutes on a reef dive (and 1h 40 in really shallow water) on a single 80 so maybe it’s not all that far fetched. I know when it’s cold and I’m working a bit hard the rate goes way, way up.

It would be nice to have a consensus between agencies on this topic. Maybe ISO will define it some day.

 

 

Shearwater Predator – I want one! November 5, 2009

Posted by Chris Sullivan in Equipment.
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The Shearwater Predator, an upgrade to the already wonderful Shearwater Pursuit is on my Christmas list. Right after I get back from my upcoming trip to Florida I’m going to work on the upgrade. The 2 big changes to the Pursuit are:

  1. A larger, OLED colour screen. The extra size and brightness should allow me to delay buying that prescription mask for at least a couple more years.
  2. Bluetooth instead of Infrared communications to the computer. No more juggling my laptop and and dive computer on the train on the way to work. Just turn the computer on and put it back in my laptop back and download the dives.

I’m so glad the upgrade is available. If I were buying one now, I would have opted for the open-circuit only version that’s new in the Predator, as I’m doubtful I’ll ever get a rebreather, but the buyer’s remorse is way less from at least being able to upgrade it a reasonable price.

Solo Diving Together November 3, 2009

Posted by Chris Sullivan in Dive Log, Training.
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No, this isn’t a harangue about “same day, same ocean” dive buddies. I’ll save that for another time. On Saturday (October 30th) we headed up to Big Bay Point to finish our solo diving course. The purpose of the in-water exercises is to promote self sufficiency. For this reason, we spent some enjoyable moments having our air shut off, are masks removed, and ourselves entangled in line.

We all had our own issues. I’d not thought everything through properly. I took the backup reg set from my technical setup for the AL80 on my back, and one of my deco regs for the pony. I’d not realized that this would only give me one LP inflator, which meant that with my dry suit I’d have nothing to use for my BC. It had been 26 years since I’d dived using oral inflate only but rather than switching over to my recreational reg with its “extra” second stage, I decided it would be good practice to try it on this dive. Despite what you might read about *OMS) bungeed wings being impossible to inflate orally, I had no problem with it, although I did have to blow a little harder than with a regular wing.

After dropping my pony bottle (more like a quarter-horse bottle as I used my Faber steel 45) on the bottom, I did my giant-stride off the end of the dock and releasing the minimum amount of air to submerge, fetched it and hooked it on to my BC while swimming out to the descent line.

The first exercise was replacing my mask with my spare. I was glad to do this as while I always carry one, I’ve never actually practiced replacing it. I didn’t find it difficult, although it took a while to get the pocket open, retrieve the mask, orient it properly and put in on. The first time through this exercise we were on the bottom. Following that we did the out of air drills. This didn’t go so well. Inadvertently I’d looped the regulator hose around the bottom clip, so it would not pull out. So I had to lean forward to keep the reg in my mouth while I unclipped the tank to free the hose. Manageable, I suppose, but not something you’d want to have occur in a real out-of-air situation.

After that, we did the same drills while swimming, with our friendly divemasters shutting our air down or removing our masks at various times. The hardest thing was maintaining depth without a mask. I could feel the air expanding in my dry suit and quickly moved to dump some air. I felt like I was still ascending but emptied my lungs and found that I was at about the same depth once my mask was back on as when I started. Looking at my computer log it there only seems to be small incursions so my perceptions were no-doubt amplified by my imagination.

Solo Dive

We also had lines tied around us and masses of silt blinding our vision. Perfect for a day’s outing. Both the water and the air were about 11 degrees C (52-53 F). There was little evidence of a thermocline down to 63 feet, although I’m sure we would have hit one if we went a little deeper.

That’s fall diving in Ontario, and why we like our dry suits.

BBP 20091029

Anyway, congratulations to Marty, Steve, Rich and Carlos on becoming SDI solo divers.