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Scubapro Spectra vs. Bare Duo-B May 31, 2009

Posted by Chris Sullivan in Equipment.
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As I’ve mentioned before, I bought a Scubapro Spectra mask in March and I’m really happy with it. The mask fits great, sticks to my face like a suction cup, is comfortable, looks good, and clears in one blow. So I was extolling the virtues of the mask to Steve, another instructor candidate in my class, but he found that the Bare Duo-B fit him better. Curiously, an identical Bare mask (except for its colour) did not fit him so well.

When we were in the pool on Saturday practicing our skill demonstrations, I noticed that his mask bore a striking resemblance to my own, and we compared it section by section to discover it was identically built in every respect. My guess is that the masks sit on display or in the box and get a bit misshapen from their factory condition, and so initially fit better or worse even though they are no different from one another.

I don’t know who paid more for his mask, but at least I like the copper and black colours I got with my Scubapro Spectra the best.


Sunday at Gulliver’s Lake May 31, 2009

Posted by Chris Sullivan in Dive Log, Training.
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Gulliver’s lake is a small body of water near African Lion Safari in the Hamilton area. Last Sunday, May 24th, 2009 which was also Queen Victoria’s 190th birthday, our group of 6 prospective PADI Open Water Instructors headed out for a very civilized 12PM start. It turned out to be a very nice day to be out diving. Gulliver Lake is good place to practice OWSI skills the Instructor Examination (IE) is held there.

After quickly setting up, we went through our briefings. I was given the free descent with reference from the Open Water course, and approach from the behind (I decided that this would be done underwater). Neither of these were a problem, and I used minimal notes to do them, which of course is what will happen when I’m actually teaching. In the IE, there is a very well-defined format for the briefing, and you get scored for hitting each and every point you’re supposed to make. I’ve been trying to reduce the preparation time and only put the key points on the slate so the delivery is more natural. I’m finding that it works pretty well.

We were in the water at about quarter to one, and I took my “students” through the rescue exercise first, as it was being done on the surface. I had my “assistant” watch the open water students, while the rescue divers did their drills. It wasn’t hard to pick up the mistakes – pressing the deflate instead of the inflate button, lack of communication with the “victim”. I lost points for not making contact with the assistant until it was over, so I must remember to look at them more.

Prior to taking the Open Water students down, I sent the assistant down to the platform with the rescue students to wait for us. It was a simple way to get them out of the way and to have them ready to go when we got there. On the descent, which was a good hour and half after we entered the water, at first Marty didn’t descend while Yoon was starting down. I thought that was the issue and brought Yoon up to the surface so I could talk to Marty. However, I hadn’t noticed up to that point that Yoon had after the 5 point descent drill sneakily switched over to his snorkel. He did the same thing on the second try and I caught it before his head was below water. So up we went again. The third try Marty went down head first and finally on the fourth attempt everything was fine and we joined the others on the platform.

From then on, my only duty was to play student, screwing up my skill demonstrations in various ways. I was a little mean with Marty. I was doing the fin pivot with oral inflation and just to make it harder for him I took the regulator out of my mouth, pressed the power inflate, and put the reg back in my mouth (blowing bubbles all the while, of course). I didn’t have the inflator anywhere near my mouth but he still had a hard time figuring it out, but he just gave me the do it again sign indicating that I should use oral inflation and that got him through it.

My other favourite was with Yoon. I was tying underwater knots. In the exercise, we were just supposed to make the knot without actually tying up to anything. I tied a nice bowline to buddy’s BC in record time and looked proudly back at my “instructor” for congratulations, which weren’t forthcoming.

It was a bit cold and despite the minimal depth (15-20 feet) I was down from my starting pressure of 2800 PSI to only 300 when I surfaced after 71 minutes of bottom time. On the surface we did our non-breathing diver drills, and finished up with a mask, snorkel and fins swim across the lake and back. To my surprise, I finished way ahead of everyone else and used it as an opportunity to promote my Scubapro Jet Fins.

Out of the water, we did our debriefings which are by now pretty easy (must remember when pointing out the solution to a problem to also point out the value – e.g. if you’re descending with your snorkel you won’t be able to breathe, remember the 5-point descent and you will have air below the water).

A long day at the lake, and home by 7:30. The next day I ran into a guy on my train to work who is also doing his Open Water Scuba Instructor Course and was at the same lake the day before.

A funny thing happened… May 26, 2009

Posted by Chris Sullivan in Training.
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Yesterday I took the train to work as usual and pulled out a section of the PADI Instructor Workbook to review. The guy sitting across from me said “I’m taking that course as well”, and then went on to tell me that he was out at Gulliver’s Lake the previous day practicing for the upcoming Instructor Examination.

I told him that I was also at Gulliver’s Lake for the same reason and had the same IE coming up. Quite a coincidence! He said there were about 2 dozen candidates, the largest ever apparently, going to IE. His group, whose instructors aren’t affiliated with any dive shop, is larger than ours (which is 6 people).

He also told me he was a Linux consultant for IBM, so not only did we discuss diving but various computer-related topics. Amazing who you can run in to. Diving – go places, meet people, do things!

Friday night in the pool May 25, 2009

Posted by Chris Sullivan in Training.
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May 23, 2009. The troupe of 5 prospective instructors, Matt, Yoon, Steve, Marty, Jim and I all headed up to Tim’s Diving Supplies just outside of Barrie to rendezvous at 5:45 pm after work for training in the shop’s private pool. On the way I stopped at the dive shop to top off my tanks, which were still half full of 50+ Nitrox from the Oriskany trip, so would have been still quite well enriched even after the air was added. I didn’t bother testing the mix as the pool is only 10′ deep, well above the MOD of pure oxygen, much less a 40ish mix.

The first order of business was to run through the briefings for the skills we were going to teach. Mine were snorkel to regulator exchange for the open water class, and the quick reverse from the rescue class. I’d prepared the first in detail using the PADI slate, and although a bit long winded it was thorough. For the quick reverse, I’d been unclear on the scope of the training so had only done the reading, without further preparation. Open water instructors can teach anything up to Divemaster so it’s only fair to ask for demonstrations and evaluations of the skills in these courses. I’m a lot less  clear and definitely less practiced in these, so I have a greater level of anxiety when it comes to this part of the training.

However, for the briefing I did fine, and got all the main points in. In fact, as I’ve found before, where I have detailed notes I tend to be long-winded, which is definitely not helpful, so the rescue  skill was actually delivered more succintly than the snorkel-reg exchange.

Next we were in the pool to do skills circuits.  Again no problem. We all did fine. I’m starting to get very comfortable will all of these and slowing things down. Unlike before, the scuba unit remove and replace is more smoother now, and I followed the instructor’s lead by planting the tank on the bottom of the pool in front of me for additional stability.

The snorkel-reg exchange was fairly uneventful. My students intentionally screwed up by (a) not doing the exchange and (b) lifting the head out of the water. I caught both of these. The only thing that I need to improve is contact with the certified assistant. Their job is always to watch the other students while your busy with the one performing the skill, and to score full marks you have to at least make contact with them between students to make sure everything is going the way it should.

On the quick reverse, everything was fine except that I failed. On the 3rd try, the pretend victim climbed on the rescuer. I was not concerned as in my own rescue class this happened frequently. It looks, though, like this shouldn’t have been allowed as this places the rescuer in jeopardy. Something I won’t forget. The other screw-ups were getting in too close and incorrect positioning which were both caught.

At 11:30, after doing the debriefings and hearing our evaluations, we were done and away before midnight. It was an hour drive to get home, and I hade to pick up some groceries, and  in bed well past my usual time at 1:20. The next morning the alarm went off at 7:30 so I could have a decent breakfast, watch the F1 qualifying at Monaco, and head up to the shop to resume classes at 9:30.

DSAT Tec Deep Training Dive May 22, 2009

Posted by Chris Sullivan in Dive Log.
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My first divemaster experience with Tec Deep was with a training dive on July 13th, 2008 for Andrew, Mike and Jeff with Brad instructing and Dave as the other assistant. For me, it wasn’t so much an opportunity to help but to observe, as I was still trying to get comfortable with all my new gear whilst wearing a dry suit. We were at our usual training ground of Big Bay Point, at the southern entrance of Kempenfelt Bay in Lake Simcoe.

The student were in to practice don/doff of the scuba unit and valve shutdowns. The former exercise is particularly difficult in a dry suit, as the scuba unit is very heavy and the dry suit is buoyant even when deflated to the point of pain. So I was amused to watch the struggles to stay attached as the divers held themselves down in a cloud of silt while trying to pull themselves back into the harness. This is a really exhausting exercise and Mike was ready to give up on technical diving afterward. Fortunately he stuck with it and we’ve done some deep diving together since then.

At one point Mike and I got lost in the silt cloud and couldn’t find the others. They’d move up current to get out the clouds while Mike was struggling back into his gear, and we had to surface to find them again. We were actually up for 14 minutes before we decided to go back down after locating their bubbles.

I was just about to buy my 7mm Scubapro wet suit at the time, and probably could have got away with it as at maximum depth (only 36 feet) the water temperature was a balmy 19C (66F). On the other hand, with the dry suit, I could go without a hood and still be comfortable.

We did two dives 52 min and 29 min, we out of the water at 11:45. Air temperature was 24C making for a nice weekend outing.

Next stop was Brockville, to help out with the wreck diving course and try the new wet suit.

Diving the Wolfe Islander II, Kingston Ontario May 20, 2009

Posted by Chris Sullivan in Dive Log, Shipwrecks.
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The third dive of my one day trip to Kingston on July 5th, 2008 was on the Wolf Islander II. This wreck was the only one which was sunk intentionally, having served out its days as a ferry to Wolf Island. We observed its replacement, the Wolfe Islander III, on the same day and I hope I’m diving long enough to visit it also on the bottom (after a natural lifespan, of course!).

The wreck was somewhat shallower than the first two at a maximum depth of 76 feet, and the water was considerably warmer at 16C (65F) – almost bathtub temperature for we northerners. I was diving EAN36 to continue my Nitrox experience and also to minimize the Nitrogen exposure on a day with 3 relatively deep dives. The equivalent air depth was a fraction over 55 feet.

The dive is more fun that spectacular. The wreck is very clean, and we did some short penetrations without a line, never far from the line. On the deck there are various “artefacts”, including an old motorcycle, somewhat lighter for the buoyancy, where everyone likes to have their picture taken. This was one of the series lost in my hard disk crash so unfortunately, once again, no pictures. Fortunately, others have taken some fine pictures of the wreck.

After the dive I didn’t hang around for long as I had a 3 hour drive to get back home. 6 hours of driving and 3 dives made for a long but worthwhile day.

Speaking of long days, I haven’t been keeping this blog going very well lately. Aside from the pressures of work there’s the instructor course, spring (with its attendant household chores), and some fascinating but slightly mostly off-hours work testing a telephone switch for work. Fortunately though, as the diving season picks up, I’ll have plenty more to write about and no doubt some new photographs.

Fun with Decompression Models May 15, 2009

Posted by Chris Sullivan in Technical Diving.
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This is totally premature but I was messing with the Bühlmann/Schreiner equations for computing compartment pressure and came up with something halfway reasonable in MS-Excel which I thought I would show you. This illustrates a dive going to 185’ on air for 10 minutes, 110’ on Nitrox 32 for 15 minutes, and 30 feet on Nitrox 80 for 20 minutes. Beware that this is a rather unlikely dive profile I made up just for illustrative purposes and I don’t recommend you dive it. In fact decoplan recommends a 2-3 min deco stop at 40′ depending on the gradient factors, although without gradient factors it doesn’t require any.

All pressures are in Pascals. Standard atmospheric pressure is 101.3 kPa, or 101,300 Pa. The purple line with the square dots represents the initial state with all compartments at atmospheric pressure. It is well below 101,300 Pa because we’re only representing the partial pressure of Nitrogen (using 79% of the atmosphere) and there’s also a reduction for water vapour pressure of 6250 Pa (this is Buhlmann’s value, about 5% of the total, there are more conservative values used by others) which I’ve assumed to be present under all conditions.

The light blue line with the triangular dots represents the state after being at 185 feet for 10 minutes. The fast compartments on the left “fill up” quicker than the slow compartments on the right which hardly move. Note that I’ve ignored the time it takes to descend to 185 and assumed that the diver is instantaneously transported there.

The next depth, 110 feet, is on 32% Nitrox. You can see that now the fast compartments off gas quickly to approach the ambient partial pressure of the 68% Nitrogen at that depth while the slower compartments continue to load up. The crossover point is between compartment 2 (8 minutes) and compartment 3 (12.5 minutes).

Finally, we go to 30’ on EAN 80 and stay for 20 minutes. The partial pressure of Nitrogen is less than 40% at this point, meaning that it is less than at the surface. So compartments 1 and 2 both end up off gassing more Nitrogen than they started with, as you can see from the purple line with the star-shaped dots. This is why we love our highly enriched mixes on deco, although this extended stay really racks up the time on the CNS clock.

The highest point on the graph after this 40 minute excursion is compartment 5. The faster compartments to its left went higher but off-gassed quickly, the ones to the far right barely moved. Next step is to overlay M-Values on this graph to see at which point, if any, that it is safe to surface. With the maximum pressure at the end of the dive around 30% over ambient, I’m guessing we’re safely decompressed by the end. It might also be interesting to look at the M-Values at 8000 feet above sea level, to see how flying after diving might affect things.

After adding the M-Values, I’m going to take a look at including the ascent and/or descent rates in the model. I will email the spreadsheet to anyone who asks. WordPress won’t let me post it here as it doesn’t support Excel. It’s a PDF file so you will need Adobe Acrobat Reader to view it.

Deco Model

Dive Plan

Time            Depth               Mixture

10                   185                    Air

15                   110                    EAN 32

20                     30                   EAN 80

Bubbling blood May 13, 2009

Posted by Chris Sullivan in Miscellany.
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I noticed this news article in the Oklahoman, and noticed a couple of things. One, as you’d expect from a landlocked state, it states that each 34 feet of depth equals one atmosphere – obviously catering to fresh water divers. Another is that it mentions Aquarius, an underwater habitat created by NOAA, where Doug Arnberg who came to one of our dive club meetings did some rebreather work. Lastly, it described taking a blood sample from an inhabitant of Aquarius, where tissues are fully saturated, and bringing it to the surface – resulting in the explosive “boiling” of the blood. That would be a cool demonstration to dive students!

I say “boiling” and not boiling, because while the phenomenon resembles boiling, it is not water vapour coming out of solution but dissolved gas, which is quite a different thing altogether, but still results in bubbles.

Half-times and parallel compartments May 12, 2009

Posted by Chris Sullivan in Technical Diving.
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I realized a couple of days after writing my last post about half times what the whole point of Bühlmann method of having the same compartment numbers for Helium and Nitrogen, but with different half times (these being proportional to the square root of the molecular weight of the gas, no less). When diving with trimix, for instance, you would add the partial pressures of the two gases in each compartment together to get the total inert gas pressure. For convenience, these pressures are measured in feet or metres of water.

The pressure in each compartment is then compared to the M-Value for the compartment to see whether the compartment pressure is more or less than the allowable overpressure  at the surface (or decompression stop, as required), and this becomes the basis of the decompression calculations. Some methods use the same M-Value for Helium as for Nitrogen, but Bühlmann has different values, and the accepted method is to linearly interpolate the He and N2 M-Values using the ratio of partial pressures in the compartment.

One of my new year’s resolutions was to not try to attempt writing any decompression code but I’m starting to feel it might be fun, now that my understanding of the topic is beginning to grow. Perish the thought. Well maybe just a little in MS-Excel.

PADI OWSI Day 2 May 10, 2009

Posted by Chris Sullivan in Training.
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In the morning of Day 2 we covered two more classroom topics

  • PADI Scuba Diver and Open Water Diver Course
  • PADI Continuing Education Philosophy


  • Adventures in Diving Program
  • Prescriptive Presentations

The prescriptive presentations cover a particular question (the scenario is that some student divers get that question wrong), and have to include a number of elements, including relating the question to (PADI) continuing education and equipment ownership. Another element is to “take the students diving” which means to talk about upcoming dives that the students will go on. For that, and for continuing education, I missed including the dates of the dives and lost a few tenths for that, but otherwise got all the elements in.

Another long day, from 9AM to 5PM with 40 minutes off for lunch. Now back to work for the week. Next stop is the pool training a week from this Friday.