Intro to recreational deep diving

[String]

A simple manual dexterity/coordination test usually brings it out.

Or taking them by surprise and asking them to perform a simple diving skill such as a fin pivot, mask clear etc whilst videoing it. Then show them the ham-fisted fumbling they make of it.

The puzzle tests are pointless - Such an improvement in a human in doing a test first time to second time it masks any difference underwater that maybe due to narcosis slowing it.

Regarding steel tanks unless american tanks are massively heavier than the ones used in europe its not an issue for a single. Yes the wetsuit compresses but it doesnt lose ALL its buoyancy. In the water a full steel 12l tank is less than 2kg negative.

 

[TSandM]

I guess the test depends on your environment and the diver's skill level. I wear 5mm gloves. I don't think I could put my mask on with my gloves on even on the boat.

I hope the smiley face means you don't really mean this . . . Because if somebody kicks off your mask at depth, you're going to HAVE to be able to put it back on!

The steel tank and wetsuit thing has to do with the very large loss of buoyancy that you have, when you take thick neoprene to depth. You can lose up to 20 lbs of lift from a 7 mil suit at 100 feet -- if you're diving a steel 130, say, and you're near the beginning of the dive, you can be ten pounds negative from gas as well. If you lose all lift from your BC at that point, you are 30 lbs negative that you have to be able to swim up. An aluminum tank will simply ensure that you are carrying more ditchable weight, but in a single tank, you're likely to be carrying ditchable weight, anyway (steel OR aluminum). In steel DOUBLES, you may well not be carrying any extra weight, and then you're on the bottom, thirty or more pounds negative, in a world of hurt.

It's a good exercise to try over a benign bottom, to dump your BC and see if you can swim your rig upward easily. (You have to do it fairly deep, if you're doing it in a wetsuit, to make the test useful.)

 

[bleeb]

Or taking them by surprise and asking them to perform a simple diving skill such as a fin pivot, mask clear etc whilst videoing it. Then show them the ham-fisted fumbling they make of it.

The puzzle tests are pointless - Such an improvement in a human in doing a test first time to second time it masks any difference underwater that maybe due to narcosis slowing it.

You can take the following with a bucket of salt but from what I've read, a dangerous and insidious early symptom of narcosis is the gradual loss of cognitive power (thinking, reasoning, multitasking). This seems to tend to start at shallower depths than the original recognized and more blatantly obvious 'raptures of the deep' (loss of co-ordination, euphoria, etc.). Using the alcohol analogy, it's like being close to the legal limit than stumbling drunk.

With loss of cognitive power, puzzles or mechanical tests like the afore-mentioned knot tying aren't particularly good for measuring narcosis, especially if you practice multiple times. You need something that makes the person think and react with something more than reflex. How well do math problems really work? Like puzzles, I thinking they're probably a bit single-minded, and don't involve co-ordinating both reasoning and carrying out physical activities, something that would be more relevant to a physically skilled activity like diving. Anyone instruct with or have experienced any better tests that include multitasking?

 

[rstofer]

The steel tank and wetsuit thing has to do with the very large loss of buoyancy that you have, when you take thick neoprene to depth. You can lose up to 20 lbs of lift from a 7 mil suit at 100 feet -- if you're diving a steel 130, say, and you're near the beginning of the dive, you can be ten pounds negative from gas as well. If you lose all lift from your BC at that point, you are 30 lbs negative that you have to be able to swim up. An aluminum tank will simply ensure that you are carrying more ditchable weight, but in a single tank, you're likely to be carrying ditchable weight, anyway (steel OR aluminum). In steel DOUBLES, you may well not be carrying any extra weight, and then you're on the bottom, thirty or more pounds negative, in a world of hurt.

It's a good exercise to try over a benign bottom, to dump your BC and see if you can swim your rig upward easily. (You have to do it fairly deep, if you're doing it in a wetsuit, to make the test useful.)

Got it! Thanks!

So, it all depends on context. In the case of a wetsuit and a single HP 100, I figure I am around 17# negative at depth at the beginning of the dive (this from the spreadsheet). But, I'm carrying about 9# of ditchable weight (from the default values with Light = 0 and Integrated = 0). So, worst case, I have to swim 8# off the bottom. By the time I reach 3m, I should be neutral again.

And that assumes a 100% failure of the wing. It is possible to imagine all kinds of failure mechanisms but some are pretty unlikely.

Of course, this all assumes I am carrying the minimum ballast possible. If I am overweighted, it better be ditchable! Adding backplate weights might not be a good idea.

Thanks again!
Richard

 

[BDSC]

I just completed my AOW and have several dives to 90-100 feet and am planning several with max depth of 120 in the near future. I will be diving a single HP 120, no pony. Diving with permabuddy.

I have planned my rock bottom PSI and EANx mixtures at 1.3 PO2 at max depth and wanted any other helpful information/preperation that was out there.

Nitrogen Narcosis - Never experienced it. Tips or advice for a first encounter?

Loss of buoyancy at depth - Do you adjust continously on descent or at depth?

NDL - Not pushing it to the limit (ie 1 min remaining at the begining of ascent) do I need to account for longer ascent time in NDL? At 120 ft, using 2 minutes to reach my deep stop at 60 feet, how much NDL would you start your ascent with? (ongassing/offgassing threshhold)

Anything else to think about?

Sounds like you will be doing some diving off the coast of NC. Some great wrecks out there. I think you'll do just fine at 120, especially if you have several dives to the 100 ft range and have had no problems. Chances are you'll have a instructor or DM with you since this will be your first dive to 120. Certainly a good idea. I wouldn't worry too much about narcosis if you haven't felt it at 100 ft. I'm the same way. Of course people will tell you that you are narced and don't know it. But if you have done fine at 100 ft., 120 won't be a drastic change for you.

Just be sure to go up and down the anchor line. Sometimes the current can get pretty strong off our coast and you don't want to have to fight it or deal with it otherwise.

Seems like with all the questions you ask you are going to be a pretty good diver.

BDSC

 

[Blackwood]

Loss of buoyancy at depth - Do you adjust continously on descent or at depth?

Continuously. I descend (and ascend) neutral, or as close to neutral as possible.

NDL - Not pushing it to the limit (ie 1 min remaining at the begining of ascent) do I need to account for longer ascent time in NDL?

When you calculated your "rock bottom," did you add any of what I like to call "oh crap" time (additional gas at max depth to get situated in an emergency)?

If so, how much time did you add? Was it a minute or more? If so, you'd be eating up your remaining NDL. As was mentioned, deco isn't binary (on/off) like they teach. But if you do incur a longer ascent requirement by overstaying your plan, the rock bottom you reserved may no longer be adequate.

- open a combination lock
- tie a knot with a piece of rope
- do simple math

Personally, I find those to be sorta irrelevant when taken one at a time. Narcosis really hinders the ability to multitask. Do simple math while opening a combination lock, and then you'll really be tempting the narcosis.

 

[ScubaSloan]

I did add in a minute for a reg pass but no additional time for any deco obligation. Sounds like what I am eventually going to want to do is dive doubles, but I would like to get the rest of my diving down pat before I change the game too much.

 

[Reg Braithwaite]

I did add in a minute for a reg pass but no additional time for any deco obligation. Sounds like what I am eventually going to want to do is dive doubles, but I would like to get the rest of my diving down pat before I change the game too much.

Sloan, what I would do is this: Put together a specific plan for the dive you are doing. This will give you an estimated time to descend, time to swim to the points of interest, time to return to the ascent location, and time to ascend.

This is an "ideal" plan that assumes unlimited air and without worrying about your deco limit. Then and only then you should work out your turn pressures/rock bottom based on the actual equipment you will be diving and your estimated air consumption at depth. This may force you to modify your plan and shorten it.

Now that you have a plan that is specific to that dive and takes your gas consumption into account leaving you a safe margin to work out a problem and return to the surface with an OOA buddy, consult your NDL table or work out your NDL. Shorten your dive if and only if your existing plan including turn pressure/rock bottom violates the NDL.

I don't want to read too much into your posts, but it sounds like you are starting with the NDL and working backwards. When visiting wrecks, you might think "I'll just dive down and stay for ten minutes then return to the surface," but speaking as a fellow neophyte it is better to be more specific.

How long to swim to it? How many times around it? How long to swim back? Or whatever the plan is. Try your best to plan the dive first, then adjust for gas, then adjust for NDL.

JM2C, and now I have to plan my own dive this Sunday onto the Tiller.

 

[Jimmer]

Reg, sorry for the hijack, who are you diving the Tiller with?

 

[Reg Braithwaite]

Reg, sorry for the hijack, who are you diving the Tiller with?

Dan's Dive Shop. Please PM with any further questions or suggestions for other charters, like maybe those in Lake Eire