Diving in the News, 2012/9/8 September 8, 2012
Posted by Chris Sullivan in Ecology, Emergencies.Tags: Adventure, Altitude Diving, Crater Lake, DAN, Diving, Diving Accident, Diving fatality, Dry Suit, embolism, Guiness Book, Lost Diver, Outdoors, Quagga Mussels, SMB, Sport, St. Lawrence River
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Coming up from dive in the open ocean and not finding your boat is a scary thought, and in the ocean and on most other dives I carry an orange SMB, a reel and even a regulation whistle in case this happens. If you don’t have an SMB, improvise with whatever you have. In this story, the intrepid diver used her yellow bikini top attached to her fin to get the attention of a passing boater. Now that would definitely work – especially if the passing boat were full of young male divers. There’s some recent additional discussion about SMBs in Scuba Diving Magazine (and if you want to know, I’m on the “con” side because equipment can’t replace judgement.
A Riviera Beach, Florida man surfaces too quickly and gets taken to hospital. Nothing is mentioned about symptoms in this video. Whilst it’s good to err on the side of caution, and yes, you can get an gas embolism by holding your breath and coming up just 4 feet, I think in the absence of symptoms I’d just watch this guy who bolted from 6-8 feet for a bit rather than rushing him to the emergency room. I’d be interested in what DAN would have to say, and of course you can call there hotline for no charge if you want to know what to do, even if you’re not a member. I liked the expression “taking on water”. I assume they mean some water got past his regulator and it panicked him. Happens sometimes.
A man in Ireland wants to break the cold water open ocean scuba diving bottom time record. There’s a record for everything these days (except deep air, due to the number of deaths, which is not good publicity for beer that’s good for you). What made me laugh in this article (other than the reason for aborting his first attempt) was the bit “when he will be exposed to temperatures of less than 15 degrees Celsius”. My goodness 15 degrees! Now I won’t scoff at how cold that is after 15 hours but it’s hardly the Arctic ocean kind of cold, or even the Georgian Bay kind of cold, or anything in Canada after mid-October. Having dived comfortably myself in 3 degree water it does sound a bit hyped.
I don’t know what to say about this article on the dead fish in Lake Erie, maybe because it’s not directly about diving. While the Ministry of the Environment says it might be from natural causes, I’m sure most people have suspicions that lay elsewhere. A follow up article confirms that it was caused by a temperature inversion, a natural phenomenon.
It should go without saying that scuba diving while high on cocaine is a bad idea. I don’t think I’m stepping out on a limb by saying cocaine itself is a bad idea. But scuba diving is enough fun all by itself, and is a lot safer when you have your wits about you.
Crater Lake, in Crater Lake National Park, Oregon is in the news this week, over a scuba diving closure due to fear of invading species. This article actually makes me want to dive there, but I understand the reasoning having first-hand experience with Zebra mussels and Quagga mussels on my own dives in the Great Lakes and St. Lawrence River.
Diving the Roy A. Jodrey September 6, 2012
Posted by Chris Sullivan in Dive Log, Shipwrecks, Technical Diving.Tags: Adventure, Brockville, Decompression, Diving, Outdoors, SCUBA, Scuba Diving, Shipwreck, Sport, St. Lawrence River, Technical Diving, Trimix, Wreck Diving
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I once described this as my “Pinnacle Wreck”. I’m going to have to change that designation to the either the Andrea Doria or the HMCS Canada, which are both at 200’ +, although there are definitely more visits to the Jodrey in my plans for the future – maybe even in the next few weeks.
Monday September 3rd was another perfect day to end a perfect Labour Day weekend, with morning coming without a cloud in the sky. We set out from the Caiger’s Motel dock, just a few minutes east of Rockport, Ontario, with Captain Mike at the helm and the same divers as the day before. However this time we planned to move the recreational divers to another boat after clearing customs. We did this so the boat manifests wouldn’t have to be changed at the last minute to give US Customs one less thing to worry about.
US entry took about 15 minutes, mostly because the other boat was slow. It was also right about then I realized I’d left the keys in the Highlander which was parked back at Caiger’s, but I had to put that out of my mind. We had the same agent as the day before, known to me only by his name tag (“Rufa”), who I’d also seen on trips in other years. He had seen all of us the previous day and actually smiled, and noting we were planning to dive the Jodrey, encouraged us to return to Canada alive. After discharging the recreational divers it was a short chug upriver to get to the dive site, right next to the US Coast Guard station. The others went in the opposite direction to the Keystorm and America.
The weather was very calm, and we took our time getting ready, going over the plan, some emergency procedures (one to Mike, “if you see an SMB while we are on deco, drop this tank in the water for us”), and after entering the water assembled near the shore to sort ourselves out and rest (if you’ve ever climbed out of a dive boat with doubles and stage bottles on, you’ll know why we rest). With Brad in front and me out the back following Matt and Rob, we headed toward the channel and hopefully finding the ship this time.
We headed diagonally from the entry point toward the centre of the channel and slightly downriver. It dips into a sort of a bowl at around 30′ before turning into a steep wall. As with the day before, we stopped at various intervals on the descent to rest, regroup and keep our heads clear. There was a mild upward current as we went over each ledge, which added to the descent time a little, but the worked well and we were in good shape by the time we reached 150′ and started moving with the wall to our left hoping to see the wreck. By the time the bow end of the wreck slowly became distinguishable from the rocks in the gloom, we were at 175′.
Rob stuck close to the wall and I noticed that was going into a confined area between the ship and the wall. Like the previous day’s dive on the Oconto, as I started signalling with my light he noticed what he was doing and turned around. We examined various stairways and holds and in one section, where I realized that it was well lit and open, I decided to go for the maximum planned depth of 190′ and started a slow descent. At this point, Brad signalled for everyone to leave. We were only 15 minutes into the dive and everyone wondered why, but it turned out to be a miscommunication between Rob and Brad over the amount of air he had left. Better safe than sorry so I had to be satisfied with 185′, which I must say is plenty.
It will take a few more visits to really get a feel for the wreck. Now that I’ve been there once I can be less concerned about the execution of the dive and spend more of it actually checking it out. Of course, I’d no doubt remember more of it if I’d used Trimix. I must take that course some time.
Despite the abbreviated bottom time, we were thrilled to have finally added the Jodrey to our log books, and really had a great time recounting the dive on the trip back. My Highlander was still there when I got back, the drive home took only 3 1/2 hours even in the long weekend traffic (It sometimes takes more than 5), and my wife had cooked me a lovely dinner. All in all a perfect end to a perfect weekend.
The Healthful Effects of Deep Diving September 5, 2012
Posted by Chris Sullivan in Fitness and Nutrition, Technical Diving.Tags: Adventure, Brockville, Diving, Drift Diving, Narcosis, Relaxation, SCUBA, Scuba Diving, Sport, St. Lawrence River, Stress, Technical Diving
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Maybe just diving in general. Mind you, I’m speaking subjectively with a sample size of one, so statistically this means absolutely nothing.
In the days leading up to last weekend’s diving, I was wondering if I was starting to get too old for the technical diving I’m doing. I’ve had issues with a torn meniscus (makes my knee a little stiff), and some days I get up and don’t feel 100%. When I left for Brockville on Saturday morning I felt OK, but I was a little edgy, and wondered if I should be diving at all, especially the 170′ fast current drift dive in dark water with limited visibility.
I’m glad I did. When I got out of the water I felt great and still feel great writing this today. What I really needed was a good dose of Adrenalin and Nitrogen Narcosis to shake off the stress of my life on the earth’s surface.
Diving the Oconto September 4, 2012
Posted by Chris Sullivan in Dive Log, Shipwrecks, Technical Diving.Tags: Adventure, Apeks Quantum, Brockville, Decompression, Dive Computer, Diving, Dry Suit, Oconto, Outdoors, SCUBA, Scuba Diving, Scuba Equipment, Shearwater Predator, Shearwater Pursuit, Sport, St. Lawrence River, Technical Diving, Vickery, Wreck Diving
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The Oconto lies in US waters a little upriver from the Gananoque bridge. It is actually just across the channel from the Vickery, and it was suggested by the owner of DiveTech that we could actually cut across the bottom from the Vickery to the Oconto by heading in the direction the Vickery’s mast is pointing. We decided to wait until next year for that adventure. Crossing a current at 190-200′ on air is not something to be taken lightly.
After finding my Apeks Quantum dead the day before, I installed a new battery, and set it up for gauge mode (bottom timer) with decompression tables written out and stowed inside a ziploc bag in a pocket on the belt of my harness. My primary computer was the ever-reliable Shearwater Predator, with Rob diving his Cochrane (plus a Quantum) and Matt using a Uwatec.
After verifying that the large shoal marker was the correct one (about 12′ square at the base) we approached in the dive boat and the three of us dropped into the water without anchoring. Like the one near the Daryaw, an Osprey was in its nest on the top of the marker and didn’t seem very happy to see us. We were also a bit downriver when we entered so we had to swim against the current wearing our doubles and stage bottles which was a bit of a workout. The bottom was shallow around the shoal marker (think about it!) and we were able to stand up and catch our breath before submerging.
We were told there was a line leading down to the wreck, but the only line we saw at the marker ran around about 1/2 its perimeter. We were also told we would go down to 30′ then up again to 10′ before going down the wall. This was also wrong, a fact not lost to us when we hit the first ledge at 54′. There is a lighthouse across the channel a little bit upriver, so our team of 3 headed off in that direction with Matt in front using his compass.
Using the narco stops plan we came up with the night before, we stopped at that ledge for half a minute or so. At 74′ I saw a line attached to a block and signalled it’s presence to Matt and Rob. We stopped again at about 100′ for another narcosis break and planned to the same at 150′ but instead ran into the Oconto at 141′ and did it there. The change in light level below 100′ was very apparent. We headed down the port side of the wreck, away from the wall and swam around and under the spars extending into the channel. Further down the wreck, and towards our maximum depth it closed in further and Rob, who was still under the spars at that time decided to turn and come to the outside at just about when I started signalling him to do just that. Wreck penetration at 175′ on air is not very safe – but without a line and on the first visit it’s just foolhardy, and I’m glad that I don’t dive with fools.
There was a large boiler on the bottom, and a couple of anchors that were nestled together. We circled around the end (or what we thought was the end, we think it actually goes further and I’ll let you know the next time we go there) and we were back at the starting point 15 with minutes into the dive. Starting at the port side, with the current pushing us along was the correct decision, as there was less current on the return trip when we were swimming between the wall and the wreck. Even so at one point I saw Matt swimming fairly hard and I cautioned him to slow down as I was concerned about his air consumption.
Now back at the bow, we checked our air and had enough left (with reserves in place) for a little more exploration and agreed on 22 minutes total bottom time (the initial plan called for 20-25 minutes). So we played around the first 30′ of the bow about more before starting an fairly uneventful ascent bang on our planned time. Unfortunately Matt cut a small hole in his dry glove hanging on to the Zebra Mussel-infested rocks, but at least it gave him the opportunity to give Dive-Tech some more business. I’ve been with lots of dry suit divers who have flooded their gloves and it’s one of the reasons I use wet gloves, even though it sometimes limits the temperatures I can dive in.
Rob and I on the other hand spent the 10 minutes or so on the 10 foot stop feed Zebra Mussels to the Gobies, and even a small Perch got into the action. We surfaced right where we started with huge smiles on our faces and our dive boat about 20 feet away. A fantastic dive with none of the narcotic weirdness of the previous day.
Dive time was 56 minutes, 22 minutes bottom time, with 18 minutes of that on the wreck. Maximum depth was 178 feet.
Introducing “Narco Stops” September 3, 2012
Posted by Chris Sullivan in Technical Diving.Tags: Adventure, Brockville, Deep Air, Deep Diving, Diving, Narco stops, SCUBA, Scuba Diving, St. Lawrence River, Technical Diving, Wreck Diving
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Despite the tongue in cheek name this is actually a serious suggestion for divers who go into narcosis territory on air. Generally accepted to begin at 100′, but sometimes experienced (first-hand by me) at shallower depths, narcosis ranges from a pleasant buzz to a creepy feeling of paranoia, and from a mild impairment to unconsciousness. On yesterday’s dive 3 out 4 team members had the creepy kind, while I had the more pleasant form. The first time I had it was on a wreck diving course at about 85′, where I had the “what am I doing here?” feeling as soon as I entered the wreck, even though I knew there were people all around me making sure I was safe. The way I managed it then was to focus on the task at hand, and I still use that along with regular cross checks to keep my mind moving.
Here’s another method of managing narcosis which we tried today, and it worked very well. Today’s dive on the Oconto (more about that later) was a little deeper than yesterday’s. There were 3 of us on the dive, and we had discussed making a slow descent as we’ve noticed that narcosis tends to be worse for a while after a fast descent. On yesterday’s dive the descent from 40′ to 175′ was only two minutes, and we thought that contributed to the heavy narcosis the team experienced at the beginning of the dive. The darkness and low visibility were also contributing factors on both day’s dives.
So we hit on the idea of stopping the descent for 30 seconds about every 50′ and today, no one had narcosis problems on the dive. The brief stop is also useful for bringing team members closer together, doing additional checks, and so on. The result was none of us had any narcosis issues. That’s not to say we weren’t narced – just that it wasn’t a problem on the dive. Our underwater coordination and decision making was good and we started our ascent exactly on time.
Deep air diving isn’t for everyone, but one way of reducing risk due to diver narcosis is to do narco stops on the way down (if PADI or another agency adds them to the curriculum, then they’ll probably call them something like “descent stops” or “staged descents”). You heard it here first.
Lillie Parsons to King drift September 2, 2012
Posted by Chris Sullivan in Uncategorized.Tags: Adventure, Brockville, Decompression, Drift Diving, SCUBA, Scuba Diving, Shearwater Pursuit, Shipwreck, Sport, St. Lawrence River, Technical Diving, Wreck Diving
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It Labour Day weekend in the Thousand Islands again. This is Ontario’s warmest deep diving water, where the temperatures are around 23c all the way to the bottom of the St. Lawrence river, which reaches depths well in excess of 200′.
Although everyone else drove up on Friday, I decided to drive up Saturday morning, leaving at 4;30 AM to get to the motel by 8AM to meet everyone. One of the main reasons for this is the light traffic, and true to form I hardly had to touch the pedals for the entire trip, letting the cruise control do the work for me.
We hung around for a bit and then headed to a dock that was almost directly across the highway from the motel. The boat held 8 passengers, and with 5 of us diving with technical gear, it was tight but manageable. The plan was to have 4 divers on the Daryaw, then head to the Lille Parsons where 4 technical divers would head for the bottom, while the other 4 waited out their surface interval and then started a shallower dive.
When I was loading my gear on the boat I noticed the battery in my Apeks Quantum was dead, even though it wasn’t very old, and there was no time to get another from my car. Rory lent me a spare computer to use as a bottom timer to go with my decompression tables which I used as a backup to my Shearwater Predator dive computer. Fortunately the Predator worked flawlessly as usual because Rory’s computer’s battery died as well.
For me, the difference this time was that I was the only diver who had actually done the complete dive before, although everyone had been in that part of the river before and Rory had done the same dive but a bit shallower. Our dive plan called for 1/2 hour bottom time with most ascent pressures in the 1000-1200psi range. Being the leader worried me a bit as the most difficult part of this diver is sticking together. Below 100′ the light is dim, visibility can be low (today about 20′) which are both a good recipe for narcosis.
We gathered on the upriver side of Sparrow Island, heading into the current but turning quickly to the right to land right on the Lillie Parsons. I lost 200 psi from my doubles due to a bad free-flow on my spare second stage. I resolved then to swap it for my ATX50 second stage on my recreational regulator which I did later that day. The last few times I’ve done the dive we just descended directly from the boat and I was a little surprised to see the Lillie. Leading the dive I went over the inverted hull and along the mast, which used to hang over the ledge but is now broken off, and started was I thought was a gentle descent. It was actually about 70′ per minute although it was probably enhanced by a downward current.
There was a little more light than last year, but I initially started swimming away from the wall when we reach the 170′ bottom until I noticed that current was pushing on my left shoulder. I turned right and briefly turned on my light to orient to the wall, turned and checked that everyone was with me and OK, and on we drifted.
The first 10 minutes flew by with everyone OK and I decided to do my first SPG check, but couldn’t find it. I became somewhat preoccupied with this situation, as not knowing my air supply is clearly something that could cause some discomfort. After a couple of minutes of checking I turned to look for the others and only saw 2 divers. Rory had suffered severe narcosis and ascended, ending his dive quite early. The trouble on this dive is that there’s no point searching for lost divers as the river just keeps on pushing you along, so we continued our dive confident that Rory was self-sufficient.
Still searching for my gauge I got Matt’s attention and tried to get him to find it for me. He admitted after the dive that he was too narced to understand my signals. I started to think about what I should do and decided to ascend early if I didn’t find it soon. I was breathing at a nice, slow, steady rate and expected that my air consumption was about what I’d calculated on my dive plan. Right after that we hit an outcropping of rocks and an upward current and I found myself at 120′ with Matt and Rob well above me. They seemed to be in a controlled ascent and doing all right and I couldn’t get their attention, so I continued the dive solo, dropping back to 150′ to make sure I stayed on the wall instead of in the lee of an island which was where they ended up.
As I was doing this I reached back to my left hand first stage and traced the line to my pressure gauge. It had come unclipped somehow so I clipped it where it was supposed to go, and having satisfied myself I had plenty of air left I continued until I hit the 30 minute mark and started my ascent. The ascent and decompression were uneventful. I didn’t see all the wreckage of the King but saw various bits and pieces which looked to me like the wreck. The current was light for the decompression, which lasted about 35 minutes, and I amused myself by feeding Zebra Mussels to the Gobies.
After I surface the dive boat was there with all the others waiting for me and I saw I was in the exact spot I had intended to be, over a mile from the starting point, and almost directly in front of the cross marking the site of the King. So all in all it was an excellent dive, and other than the group ascending at different times we all stayed within our plans. Tech diving teams often have a rule that if one member aborts, everyone else does too. Rightly or wrongly we don’t tend to do that, letting each member decide if they want to leave early unless they signal they want the group to ascend for safety reasons.
A Little Drift on the Lillie Parsons September 25, 2011
Posted by Chris Sullivan in Dive Log, Shipwrecks, Technical Diving.Tags: Brockville, Lillie Parsons, St. Lawrence River, Wreck Diving
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Labour Day Monday, 2011 – last dive of the weekend. I’d used my doubles down to 1800 PSI on a training dive on the Daryaw, but I also wanted to go deep on the second dive of the day, so Larry and I made a dive plan which was to drop to the bottom of the St. Lawrence and scoot along until one of us got down to 1000 PSI, leaving us lots of gas to make a slow ascent. We were expecting little or no decompression obligation but I took a reasonably bottle of 47% Nitrox along with me anyway.
The dive started at the Lillie Parsons, at the upstream end of Sparrow Island (there are a lot of wrecks in the St. Lawrence near the upstream ends of islands – go figure). There were about 12 of us on the boat. Some wanted to do the traditional dive, which is to do a lap around the wreck (which is around 50′ deep) then drift at about 40′ or so to a chain that hangs from a cove on the shore. I found out on the previous Saturday that the maximum depth of the chain+rope was 66 feet. Others wanted to drop down to 80-100′ and drift along a bit further.
There are several ways to get to the wreck. The first I learned was to drift on the surface to island in the spot where the current splits around the island and therefore is fairly calm. You can look underwater and see which way the particulate matter is moving to know where that is. Then you have two choices. One is to swim upstream then turn right with the current and run right into the wreck, the other is to find the chain from shore that leads directly to it. The third way is to just jump of the boat (parked 100 yds or so upstream) and follow the contour down from the island to the correct depth.
We’d no real interest in seeing the wreck so we just headed down. We both saw the end of the mast, which sticks out into the current, briefly as we drifted by, but couldn’t see any other part of the wreck. We didn’t exactly rocket down, but didn’t waste any time either. Usually at that spot I avoid using my dive light and just let my eyes get used to the gloom. No dice this time. At 164′ maximum depth I couldn’t see a thing, and had to use my light to avoid running into outcroppings of rock against the wall while also keeping the wall in sight so as not to drift into the channel. I also wanted to stay a few feet off the bottom which I could also not see. Basically if I didn’t shine a light on it, I didn’t see it.
After a few minutes Larry signaled he was down to 1000 psi (he had double 85s and started at 1500) so we did a nice easy ascent while still drifting along. We got into a calm spot at around 20′, so we found a good foothold at 15′ and we did a safety stop for a few minutes (me on my deco mix) before surfacing. The computer had indicated a 10′ stop for me during the dive but it was clear by the time we got to safety stop depth.
When we surfaced we were on the downstream end of Stovin Island, about 100′ from 4 of our other divers, so we swam over to them so we could get picked up as a group. To the credit of the local operators, a competitor of the operation we were using called over from their boat and said they’d radioed our boat and suggested we move to the end of the island so they’d have an easier pickup. It’s great to see a community (Brockville, Ontario) that looks out for each others’ divers.
Tec 40 Graduation Dive June 29, 2010
Posted by Chris Sullivan in Dive Log, Shipwrecks, Technical Diving, Training.Tags: Adventure, Brockville, Decompression, Dive Training, Diving, Drift Diving, Nitrox, Outdoors, PADI, SCUBA, Scuba Diving, Scuba Instructor, Scuba Training, Shipwreck, Sport, St. Lawrence River, Technical Diving, Training, Wreck Diving
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Rather than end up at our usual mud hole, on June 13th 2010, the Tec 40 students, assistants and instructor met at Caiger’s Resort along the mighty St. Lawrence River to knock off the class’ first (authorized) decompression dive. With 3 students, an instructor and 2 assistants, we had an easy time of it, with the students forming a team, but also being buddied up with a certified pro to both harry them and be around for emergencies.
The location was Ivy Lea Ontario, just a little upriver from the Thousand Islands bridge. I’d been there once before, and having enjoyed it the first time, was looking forward to doing it again. The dive consists of dropping into the river about 1/2 way along Ash Island, then drifting to a wreck known as the Ash Island Barge.
Once we’d entered the water, gathered together and done our bubble checks, we dropped over the wall to our planned depth of 125′. Actually Dave went a bit deeper to see if the students would follow him. They did, but soon caught themselves and got established at the proper depth. About 1/2 way through the drift we stopped and went through some drills, then continued on to the barge.
By the time we got there, we were almost out of time, so a couple more quick procedures and we headed up for our deco. Each student performed a gas switch on the way up to their decompression stops and soon thereafter our new graduates were floating on the surface where the boat was waiting for us.
Graduates waiting to be picked up
Because I need to log some 130+ deco dives to qualify for Tec Instruction, I followed Dave down to 132′, and used EAN50 for staged decompression. Water temperature was 15C (58F) on the bottom. We’re looking forward to diving the St. Lawrence again with some new students on Saturday. It should be even warmer.
New Shearwater Desktop Software November 13, 2009
Posted by Chris Sullivan in Equipment, Technical Diving.Tags: Adventure, Brockville, Decompression, Dive Computer, Diving, Enriched Air, Nitrox, Outdoors, SCUBA, Scuba Diving, Scuba Equipment, Scuba Instructor, Shearwater Desktop, Shearwater Predator, Shearwater Pursuit, Shearwater Research, Shipwreck, Sport, St. Lawrence River, 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.
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.
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.
Brockville 2009 & my Shearwater Pursuit October 1, 2009
Posted by Chris Sullivan in Dive Log, Shipwrecks, Technical Diving.Tags: Adventure, Brockville, Decompression, Dive Computer, Diving, Enriched Air, Nitrox, SCUBA, Scuba Diving, Scuba Equipment, Shearwater Pursuit, Shipwreck, Sport, St. Lawrence River, Technical Diving, Wreck Diving
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The deep drift dive from the Lillie Parsons to the James B. King was a good test of my recently acquired Shearwater Pursuit SPOT. I have to say it performed admirably, calculating and tracking my deco schedule as it should. The first stop it asked for was at 80′, which is about what I’d expect, but it cleared before I got there and so my first was at 70′. I had a bit of trouble finding a good handhold in the current there, and made an unplanned excursion to 68′ for a few moments, but as these are deep stops with very low gradient factors it was of no concern. The US Navy tables show 30′ as the first stop even on a square dive profile to 5′ deeper than my maximum depth. You can see in the graph from my logging program the jump in inspired Oxygen that occurs part way through the 40′ stop, when I switched my computer after switching gases.
As the stops got shallower and longer, the gradient factors get higher and maintaining stop depth becomes critical. I’d planned to switch to my deco gas (curiously 71% 02 because someone topped off my 80% tank by mistake) at 30′, but changed my mind and used it on the 40′ stop as well, as the deco MOD of the mix was within limits.
As I mentioned before from now on if I’m only carrying one deco gas, it will be EAN50, as the penalty is low and it is a good backup at greater depths than EAN80. My next tank acquisition will likely be something smaller like an AL30 for pure O2, if I feel the need to carry something else for longer dives.
Deco stops being based on exponential models often work out close to a Fibonacci sequence, where the length of the next stop is approximately the sum of the current stop and the one before. So if your 30′ stop is 5 minutes, and your 20′ stop is 8 minutes, then the 10′ stop is likely to be around 13 minutes. This was certainly true with this dive, after adjusting for the gas switch, which shortens everything. I use this principle to memorize a deco schedule that closely approximates my plan, so if I have nothing else (which should never happen, of course) I can have something close to a reasonable decompression. All it requires is for me to remember the first two stops.
Finally, I’ve mentioned the importance of a slow ascent from the last stop, where the gradient factor is highest, and you can see from the graph that I spent a full minute ascending the final 10 feet.
Chronicle of an older diver 