PerroneFord changed my thinking, n maybe even saved my life.

[rollerboi]

Hopefully, people will help you along this path and not block it by withholding information that could help you become a safer and better diver. I agree with you. The cave divers I've met and worked with have been incredibly helpful to me. I'd be nowhere in this game without them.

Perrone,

I wanted to thank you for being willing to be one of those helpful people. In my situation, I have done a lot of reading and trying to comprehend/understand. I've turned to a few of you folks (mostly Lynn, bless her heart) with more in-depth questions about things such as depth averaging, deco tables, nitrox, and so forth.

Even though I'm apparently quite the accomplished internet diver (), I wouldn't think of applying this stuff until after proper training. Nitrox and Fundies at the very least. But it is good to have an understanding, and good to have people to turn to to help that along.

So, thank you. And to the OP, best of luck in your courses!

 

[dumpsterDiver]

Im sorry, DIR, but in spearfishing, a "dive plan" simply CAN NOT be followed. You are there to find a nice fish and shoot him. He may be at 40 feet and you come back to the boat 10 minutes later with 1900 pounds of air. Or he may be at 140' feet and you are only minutes away from going into "deco" in order to get him up to shallower depths after the shot. So it's "reactionary" diving where you watch your SPG and your divecomputer like a hawk. There are a couple "rules of thumb" I apply as do most of my "spearfishing mentors". We go "deep" right off the bat... let the air out of the BC and drop straight down as quickly as possible on a "full tank" If you've got a shot at say 150'... you will have it immediately (either he's THERE or he's NOT) You take the shot. If you hit him, you got minutes to drag him up to say 120' and still not come close to going into deco. If you MISS... well... the time it took me to get there, see him, take the shot, and miss, I've used up my time... I've burned at least a minute and half there...I don't have another 45 seconds to reload my gun and try again. I just come back up. Period.

It is not DIR diving. The more I learn about diving.. the more I realize how risky this spearfishing sport REALLY IS. For example...how many people diving have ever contemplated that fact that at 5bar... a 1st stage regulator failure = "empty tank in about 12 seconds." I didn't know a 1st stage even COULD fail!

So I am beginning the journey of becoming a TEC diver starting this very up and coming week. My double AL80's are built. . I think the "cave divers" I have met are the best trained, safest, and most technically proficient divers I've ever spoken to. So I want to learn from them an apply it to "my kind" of diving.

I'm curious as to how you expect to engage in safe tech bounce diving with doubles.
Are the doubles intended to allow you to stay longer or to provide redundancy? I can think of many reasoons why doubles might not be a good idea with those types of dives.

 

[mos11b1p]

I never intended on taking doubles spearfishing. (Just getting in the boat four times is enough reason not to! I put the doubles together because my instructor and two other guests joining us this week will be diving them. Thought it would be an outstanding opportunity to learn how to use them. (Tried them in the pool this Sat. Had to adjust tank bands so I could reach the valves. Other than that...I found them easier to balance than my single.) My dive buddy (Michigan great lakes diver) uses them when we go recreational diving. Every now and then, we'll drive up to Gulf Shores, AL and do a shore dive if the tides are right...Me on a single AL80, him on doubles, full HAZMAT suit, and 40cf pony with valves that tie it all into a full facemask. We're diving depths of a whopping 20 feet. I think I could stay down "FOREVER" on a set of doubles and that would be fun. Lastly... though I have been told I will truely enjoy cave diving, I like diving wrecks and would like to put my tech diving skills to use in that arena. Spearfishing 30 miles off shore in the Gulf is a "sport" to me...but I also enjoy booking a seat for a leisure recreational 2tank dive on a Saturday afternoon out of Panama City, or going on open water checkout dives with students from our dive shop. Diving al80 doubles will fit nicely in those environments.

 

[mos11b1p]

NEW QUESTION: I found that at a depth of 14 feet in pool water, with only 150 pounds in the doubles set, wearing my 7mil suit and 5mil hood,...I needed four(4) pounds of additional weight to remain perfectly neutral. (the only foreseable change to the configuration is "add a 10watt HID to the equation")

So I put two 2pound sacks in a nylon weightbelt and slipped it around my waste on the outside of my harness, and I was good to go. Im diving wet in a 7mm suit. Here is my concern. When diving a single AL80, speargun in hand, I have NO ditchable weight, am a "hair positive" near the surface, neutral at 15feet...and DROPPING LIKE A ROCK at 40 feet. (I'm only wearing .5(half mil) suit though. I have no trouble swing THAT rig deep with no air in the BC.)

I know I should be able to "swim my rig" in AL doubles wet too. I don't know how to determin just HOW MUCH lift I loose once I get to...say....100feet...in that 7mil suit, but my gut is telling me it is going to be HARD TO SWIM because of such a large change in lift on the wetsuit. For this reason...I ditched the "tank band lead pouch pockets" I normally use...and actually put that minimal four pounds into my weight belt (the one I bought for open water class and never used again) so that I can at least ditch the extra four pounds. I guess the only real "test" I can do is take the doubles set down to 100 feet or whatever, wet, let the air out of the BC, hand the weight belt to my dive buddy, and see if I can swim the rig back up, right??

 

[PerroneFord]

I guess the only real "test" I can do is take the doubles set down to 100 feet or whatever, wet, let the air out of the BC, hand the weight belt to my dive buddy, and see if I can swim the rig back up, right??

Remember that your suit will be un-compressing on the way up. So you won't have to swim it to the surface, but probably only 40-60ft before the uncompressing of the suit begins to catch up with the lack of air in the wing once the weightbelt is out of the equation.

And it's a great experiment to try in 100ft of water somewhere.

 

[roakey]

This was the start of it all: Deep Safety Stops by Richard L. Pyle. Though not the original "inventor" of deep stops, I feel that he was the one that got the ball rolling.

Roak

 

[sschlesi]

There is no cut and dry answer.

Not all parts of your body on/offgas at the same rate. Note that I bolded the word blood in your post. It's generally accepted that blood is among the fastest tissues in the body. At any given depth there is an ambient pressure, and that corresponds to the saturation pressure (highest pressure that will eventually be reached in the tissues without further increasing the ambient, i.e. descending). Many decompression models assign blood a halflife of 5 minutes. That means that, at any given depth, your blood will more or less stop ongassing after about 25 minutes (when it's reached 97% capacity). That's true at the surface, at 20 feet, and at 200 feet. The difference between those levels is the pressure to which the tissue saturates.

Those tissues which have ongassed enough to raise their internal inert gas pressures to greater than the ambient pressure at the level to which you ascend will offgas. Those tissues which are substantially slower (bone, fat, cartilage, etc.) may still be ongassing.

The question is: do you care? As a diver, your main concern from a decompression standpoint should be Type II DCS, or DCS that attacks your central nervous system. Theoretically, it's bubbles in the fast tissues that cause Type II DCS.

In a recent thread in the Ask Dr. Deco forum, Dr. Deco said

Halftimes

There is experimental evidence to suggest (from me) that the tissues are the same and the halftimes are just a mathematical concept. That is a standard concept and has been acknowledged for about thirty years.

I wouldn't rely on clearing of the "fast tissues" to protect you from DCS.

 

[Blackwood]

^^ My posts all carry the same disclaimer that it's theoretical information only.

Whether or not the halftimes in the model accurately represent what's happening physiologically as a side issue, I'd question how you'd suggest planning dives if not by using one of the established tables, all of which have some basis in exponential loading.

 

[mos11b1p]

In a recent thread in the Ask Dr. Deco forum, Dr. Deco said



I wouldn't rely on clearing of the "fast tissues" to protect you from DCS.

After doing some studying and searching, I have become aware that there is an ENORMOUS amount of research that has gone into the "science of microbubble" offgassing, as expressed in modern day dive computer algorithems. My inclination is that I do not necessarily need to (at this stage) understand the science fully, to be able to appreciate it, respect it,...AND FOLLOW IT RELIGIOUSLY. That, and doing all the "basics" that we ALL know we should be doing (i.e. staying hydrated, staying warm, avoiding vassoconstrictors such as cafine and nicotine, avoiding alcohol...etc.) II can't honestly say I'm "relying" on ANYTHING to "protect me from DCS." What other options do we have than to BELIEVE in the research findings that have led to modern tables, TRUST the technologies that have captured those tables in algorithmic form, DO "all the right things" and then...simply DIVE and ENJOY?

 

[sschlesi]

^^ My posts all carry the same disclaimer that it's theoretical information only.

Whether or not the halftimes in the model accurately represent what's happening physiologically as a side issue

I was trying to point out that it appears the tissue compartment theory has been proven wrong. If tissue compartments don't really exist, any conclusions based on tissue compartments make no sense.

I just wanted people who read this thread to realize that tissue compartments don't really exist. I suspect when most divers are introduced to deco theory they believe that tissue compartments are a confirmed fact.

I'd question how you'd suggest planning dives if not by using one of the established tables, all of which have some basis in exponential loading.

I would only suggest planning dives using the established tables. The tables have been experimentally validated to produce reasonably safe profiles. Even if all the theories on which the mathematics of the tables were based are disproved, the experimental validation still stands. Better understanding will lead to better models, but the existing models will never get less safe.