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Post by SeaRat on Dec 23, 2019 14:32:25 GMT -8
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Post by crabbyjim on Dec 24, 2019 20:09:19 GMT -8
Gee, thanks John! Now I’ll have something to do on New Year’s Eve besides go all grammar police on your future posts.
What time did the first dive on Saturday begin?
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Post by SeaRat on Dec 25, 2019 22:07:31 GMT -8
Gee, thanks John! Now I’ll have something to do on New Year’s Eve besides go all grammar police on your future posts. What time did the first dive on Saturday begin? We'll say 1:00 pm for the first dive, and 3:00 pm for the second on Saturday. Concerning the grammar police, just remember that this problem was written on a manual typewriter in the mid-1970s.  John |
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Post by SeaRat on Apr 7, 2020 21:45:36 GMT -8
 John using twin AL 72s in Clear Lake by John Ratliff, on Flickr On August 25th, 1974 I dove with Larry Murphy and a National Parks Service diver, Dan Lenihan at Rubicon Point, Lake Tahoe. The dive was to 75 feet for 15 minutes, and was just after the conclusion of the NAUI High Altitude Diving Conference. It was at this conference, which the U.S. Air Force sent me to so that I could convey the information to Hq, Aerospace Rescue and Recovory Service, Pararescue, that I got the tables and other information posted above. Well, I posted this dive problem some months ago, and so far no one has tried to solve it. So I took it on at dinner tonight. Here are the results of my calculations. Saturday's DivesFirst dive, 30 feet for 45 minutes. Using the tables, a 30 foot dive corrected for an altitude of 4,000 feet should be shown as a 35 foot dive, which translates on the NAUI Air Dive Tables (above) to 40 feet. So use a dive of 40 feet for 45 minutes. This gives us Repetitive Group E when we exit the dive. The surface interval is calculated by seeing that the dive began at 1:00 PM, and so ended at 1:45 PM. The second dive becan at 3:00 PM, and so the repetitive group had gone from Group E to Group D, with a residual nitrogen time (RNT) of 29 minutes. The second dive was 40 feet for 30 minutes. To calculation the nitrogen load on the diver's body, the RNT and the actual time must be added, so: 29 minutes RNT + 30 minutes dive time = 59 minutes dive time The 40 foot dive becomes a corrected equivalent of a 45 foot dive, so we need to use 50 feet on the NAUI Air Dive Tables. Fifty feet for fifty-nine minutes puts us into Repetitive Group I at the end of the dive. Sunday's Dive We assumed that the dive began at 10:00 AM, and so the Repetitive Group went from "I" to Group "A" (as if no diving). This is because of the 18.5 hours between the Saturday last dive ending and the Sunday dive beginning. This first Sunday dive would be spactacular, diving to a gauge depth of 90 feet, with a bottom time of 10 minutes. The gauge depth of 90 feet is an actual depth of 94.7 feet (adding 4.7 feet to the depth gauge reading), practically 95 foot and on the tables that means we use 100 feet for 10 minutes. At the end of this dive we are in Repetitive Group D. If we wait 1.5 hours between the first and second dive, the Repetitive Group D goes down to Repetitve Group B. So for the secod dive, we are diving to 70 feet gauge depth (again, add 4.7 feet) which is effectively 75 feet, and we use 80 feet on the NAUI AIr Tables (above). So for a 80 foot dive planned, we need to use a RNT of 10 minutes, and add that to the 15 minutes we plan for the dive. So that's a dive time of 25 minutes at 80 feet. When we end this dive, we are at Repetitive Dive Group G. Now, for the serch dive we've been asked to do, we have 1.5 hours of surface interval, and the Repetitive Dive Group goes from G to F. We have a RNT of 42 minutes for the planned dive. The Theoretical Depth at Altitude for the 50 foot dive is 58 feet, so we must use the depth as 60 feet. The No Decompression Limit for this dive at 60 feet (real) would be 50 minutes, minus the RNT of 42 minutes. NDL Time:....50 minutes RNT.........:..-42 minutes NDT (real)......8 minutes Now you can see how the dive instructors and divemasters of ol' earned their pay. (In my case, it was simply Air Forrce pay.) John |
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Post by SeaRat on Apr 15, 2020 17:38:30 GMT -8
Anyone noticed that I worked through this problem a few days ago? (See above.)
John
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Post by nikeajax on Apr 15, 2020 18:13:22 GMT -8
Sorry John, I don't do well with algebraic equations...
Q: If Billy had two apples and his sister Inez had nine kumquats: what time would the train have to leave Anaheim to get to Cucamonga at 8:43 AM?
A: Michael Collins in 1921
JB
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Post by SeaRat on Apr 15, 2020 21:40:54 GMT -8
Sorry John, I don't do well with algebraic equations... Q: If Billy had two apples and his sister Inez had nine kumquats: what time would the train have to leave Anaheim to get to Cucamonga at 8:43 AM? A: Michael Collins in 1921 JB JB, This exercise was two-fold. First, as an appreciation for dive computers! Without them, you'd have to work through these tables. Second, if anyone wanted, a step-by-step example of what we had to do in the Good Ol' Days. Most divers actually ignored the altitude tables, and simply dove using a capillary gauge and using those readings at altitude to work the Navy tables. Unfortunatesly, or maybe unfortunately, reading the various tables is not algebra. It is simply using the tables. Again, dive computer appreciation. John PS, you've gotten me on your question. I haven't a clue. |
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Post by nikeajax on Apr 16, 2020 16:23:06 GMT -8
Word problems are absolutely no fun for me and tend to make very little sense: my brain doesn't work like yours does. So, imagine yourself standing in front of a canvas and trying to paint something like this:  JB |
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Post by SeaRat on Apr 16, 2020 17:30:44 GMT -8
JB, I totally hear you on that. Your painting is beautiful. I'm going to try a pencil drawing, or eventually a painting, soon. I took the following photos, but they don't convey what I want.  _MG_4521 by John Ratliff, on Flickr  _MG_4520 by John Ratliff, on Flickr  _MG_4519 by John Ratliff, on Flickr What I want to do is to combine the above three photos to shaw that great blue heron looking back and pecking at the blackbird that had been harassing him. He's flying forward, but his head is obstructed by the trees and his wings are in the wrong position to show his reaction to the blackbird. I almost caught it photographically, but didn't got what I want. So I'll try drawing it in. What has this got to do with the repetitive dive problem? Nothin', nothin' at all. The repetitive dive problem was simply a mechanism to get people used to the fact that diving at altitude is different from diving at sea level, in that the pressure/depth/time relationship with decompression is different. This was in preparation for our getting to Clear Lake. But that's not goin'a happen. So this was basically a thought experiment, and I used it in the 1970s as a teaching mechanism for our Pararescue Team. Now, maybe you can give me some insights into how to make these three photos into a nice drawing? John |
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Post by nikeajax on Apr 17, 2020 8:17:21 GMT -8
John, the thing with art is to convey your mood more than anything else: instead of one Red-wing, you may want a second, just to convey a concerted effort of harassment: they live in colonies! The third image shows the Heron's legs down and splayed and making a hasty exit: this shows emotion. You may be able to do a cut and paste job in a photo editing program: I use Abode Photoshop to get my layout/sketch the way I want it. I'll do web searches for the subject I'm working on, or just go out and reshoot some of my subjects: I may find a more dramatic pose. For instance: your Red-wing in a better hover. Can Herons turn their heads in flight and how far? So, speaking of art, do you ever hear about this: en.wikipedia.org/wiki/Ecce_Homo_(Mart%C3%ADnez_and_Gim%C3%A9nez%2C_Borja)PPP-BWAHAHAHAHA!  JB |
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Post by SeaRat on Apr 17, 2020 9:13:14 GMT -8
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Post by nikeajax on Apr 17, 2020 10:45:34 GMT -8
I think if you want to recreate the scene, you might want to study/do a search for Japanese paintings of Herons and Cranes from the Edo Period: I'm not saying do it in that style but look at the use of lines and how they simplified shapes to set a mood but the birds look very naturalistic. If you look at John James Audubon's work, it can be very stilted.
JB
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Post by h2operations on May 30, 2020 7:45:50 GMT -8
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Post by h2operations on May 30, 2020 7:51:11 GMT -8
Thank you for sharing the relics, most divers trained these days have no idea what these are let alone how to use. Granted the invention of the dive computer has made it easier, there is nothing better than having to run your equations on the fly because Murphy handed you bag of >>>>.
Enjoyed your FTX.
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Post by rikdog7 on Oct 2, 2020 22:19:58 GMT -8
John,
I love the math exercise. I hope it is not too old of a thread to ask a question. I think I need some remedial equipment training for a moment. I noticed on your altitude adjustment chart a capillary tube gauge with a negative coefficient that reduces the reading. In your example it would be 35 x .887 = 31ft. It does not change the ending letter designation using a Naui table, but it does make me ask a question. Are there, or were there, internally sensing depth gauges, or am I missing something? If I understand correctly that would mean the water is on the inside of the capillary and it would not be a closed tube, or bourdon tube. It seems you wouldn't want that because of corrosion. I am only used to capillary instruments for gas sampling. You have to batch purge it to remove residual gas, that doesn't seem like a good idea for saltwater.
I know I am showing my ignorance, but that is how I learn.
And yes, now that I have learned how to use a computer for diving, I do really like it.
My only complaint is that it makes it more tempting to change your dive plan mid dive. One of the core training elements I remember was, Plan your dive, Dive your plan. I guess the good comes with the bad, because I love the benefit of getting an accurate dive profile for planning the next dive during the interval.
Anyway.
Thanks again for the test.
Rick
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Repetitive Dive Problem by John Ratliff, on Flickr
Altitude Corrections001 by John Ratliff, on Flickr
