Intro to recreational deep diving

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?

You need another 50 to 75 dives before you could start tech training.

In the meantime, there are dangers in trying this on your own.

For instance, if you are diving deep with a thick wetsuit at a wall or other drop off, then this may be the last that we ever hear of you, unless you have a really good B/C-wing.

The issues include whether your power inflator can fill your B/C fast enough to compensate for your wetsuit collapsing.

I know there is a canyon like that around Norfolk, but probably not your area, though.

Add a steel tank into the mix, and you could be headed for heaps of trouble at "deep" depths. Deep is relative. And it varies for different folks.

Best to keep your depth in the range of 50 to 75 feet for awhile.

And if you want to dive shipwrecks, then take tech classes. Shipwrecks are the only things that I imagine would require such deep diving as you have asked concerning.

ScubaSloan:

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?

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I'm sure many will post as to your question but I only have a few questions.

First is why 120? Is it a just so you can say you have done it or is there a specific thing to see at that depth?

You said You have never experienced Nitrogen Narcosis? I'd say yes you have, you just did not know it.

You also said you are not pushing the NDL 1 min remaining at the beginning of ascent is pushing it - real hard.

Yes - Buoyancy is something you always adjusting. Although your wetsuit is mostly compressed, some additional changes will happen. But the fact that you even have to ask that question makes me ponder if it is smart to do that deep of a dive.

ScubaSloan:

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)

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Add air several times on the way down. If you divebomb down to 110 then hit the inflator you are not going to stop in time.(You need to put more air into the wing due to increased gas density at that depth). Might hit,130 or 140. How does that affect the dive? Do you have enough gas? Would 140 be beyond the NDL of your nitrox mix?

It makes no real difference if you are 1 minute short of NDL or 1 minute over it,you are in a wide gray area of "kind of in deco" Treat a dive to 120 as a deco dive i.e. bolting for the surface is not a sensible response to a problem.

If you are asking these questions you probably should not be doing the dive.

If you have been to 100ft, you have experienced narcosis. Didn't your AOW instructor have you do a timed exercise at depth and in the shallows to demonstrate this?

ScubaSloan:

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?

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Narcosis, well that varies between people. What kind of conditions will you be diving in? It is hard to say how you will experience it. I would usually recommend to newer divers wanting to dive to that depth, to have an instructor around, or at least someone experienced at deeper diving to keep an eye on them. Is your buddy an experienced diver?

Loss of buoyancy at depth, I am confused by this, just treat it much the same as diving to any depth. Add air when you have to and take out air when you need. You should already be doing this when you are descending to 100' so you don't hit the bottom hard.

With NDL, I would be leaving more than 1 min before I start the ascent. This question also applies to diving to any depth really. If you are diving to 100' how many minutes do you usually leave before starting the ascent?

If it were me doing a dive below 100' I would be taking an additional gas source. That is the main reason I have not done many dives below 100', I would prefer redundant air. But a lot of people don't care. Just something to think about.

How did you calculate rock bottom PSI?

Dude, no offense, but if you are asking some of these questions, you really aren't ready for this dive. Really, no offense, but all these questions apply to the dives you have already done, yet if you did them without knowing the answers to the questions, how do you feel about that? I applaud your preparation and planning and the fact that you are asking the questions at all. You are head and shoulders above the majority of divers. I would throttle this learning curve back a bit and when you have answered these questions for your self, particularly the one regarding buoyancy, you can move forward.

As a final note, like other posters have mentioned, this dive is right on the edge of deco/non deco. Remember, deco is not a black or white thing. It is not on or off. It is a sliding scale of gray and at that time and depth, the scale is leaning towards the darker end of the spectrum..... Slow down, keep learning, ask questions, and enjoy the process.

First, good for you. Asking about this here is really smart. I've been reading posts here and there is some really good advice.

ScubaSloan:

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.

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How experienced is the permabuddy? This could help if they have a lot of experience. By max depth of 120' do you mean you want to go to 120' or are you saying that you have set a personal limit of 120' (even though most agencies are okay with 130'-140'). I have set a max depth of 110' for myself; it is based on some of the wrecks I would like to dive. What is your 120' based on?

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.

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Think about worst case scenario. As others have pointed out, is the 120' a hard limit or will the environment let you go further? Calculate the depth for 1.6 PO2 and keep that in mind. Assuming your 1.3 PO2 is based on 120' max depth then you are diving 28% nitrogen. This gives you a max depth of 155' before oxygen toxicity. If the environment will let you go deeper, you have added things to worry about.

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

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Read more postings on scubaboard.com. Did you test yourself? How? If you are just going on how you felt and you were narc'd you might not have realized it. Slightly narc'd is like slightly drunk. You don't realize it until you miss that stop sign or red light.

To really know you need to do things that make you think. Some things instructors have tried are:

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

The open combination lock is pretty easy to do. You open the lock on the surface while someone times you. Do it again at depth and see how much slower you are.

Or take three pieces of rope and tie three different knots while someone times you. Go to depth and do it again. Don't do it with one piece of rope. Do it with three pieces of rope. Keep the results. Check the knots when you get to the surface. If they weren't right, do it again but 10' shallower.

For simple math, if I put my thumb up it means ADD. If I put my thumb down it means SUBTRACT. If I show you my palm I want the total. I will then do something like 2 fingers, thumb up, 1 finger (= 3), thumb up 2 fingers (= 5), thumb down, 3 fingers (= 2), palm. You then respond with the current total of 2. Someone else is timing us and recording the values and result. I'll do it again at depth.

If you and your permabuddy are doing these, get anoehr buddy pair to monitor time and air. If you are both narc'd you might not realize how long these exercises are taking you until you are out of air.

If you are doing something like these test and you did fine then you know you are not narc'd. Additionally, remember the person testing you might be narc'd. This is why I suggest bringing the results back to the surface for knot tying or having a third person time you for the hand math.

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

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I'm REALLY surprised you have to ask. If you have been to 90'-100' you should know the answer to this. Actually, if you have any experience diving to 60' you should know the answer to this.

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)

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Your wording is a little unclear but I'm going to assume you mean, you will NOT be beginning your ascent with only 1 minute remaining and you want to know how much air you need to be able to do an 30' per minute ascent and have plenty of air left. Kind of depends on your SAC rate.

Anything else to think about?

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Your buddy. Is your buddy better or worse at air consumption? Are they diving HP 120 with no pony?

What kind of exposure protection are you wearing? The thicker the wetsuit the more compression at depth, the better your buoyancy needs to be.

Is there a risk of free flow? Do you know what to do if a free flow happens?

Are you doing anything else which can add risk? E.g. wreck penetration?

Thanks for all the responses. To clarify a few things I gave the 1 minute of NDL remaining as an example of pushing the limit, what I am not doing. As a rule I leave enough NDL left to make a controlled ascent to my safety stop (though rock bottom hits before this). The 120 is to the sand at the wrecks I would be diving (I would be taking a DM with me as I like to do so on a new wreck). I calculated rock bottom based on 2 divers, stressed RMVs, 1 min deep stop at half depth, 3 min safety stop 200 PSI cushion. As for the buoyancy my question was not if you adjust, but if the effect for that last ATM on buoyancy was more noticable due to compression. I guess in retrospect a hazy question.

ScubaSloan:

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.

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How experienced is this buddy for that sort of diving? Is it going to be TWO inexperienced people trying this?

Firstly id recommend always take a redundant air source and never to have to rely blindly on a buddy.

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

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Chances are you wont notice you're suffering and thats why its dangerous. Its similar to the not feeling drunk then realising you cant actually walk when you try to stand. It affects people in completely different ways from euphoria to panic and everything in between. Monitor yourself, monitor your buddy, check the gauges. Be ready to ascend IMMEDIATELY if either of you are slightly unsure.

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

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Its the same as any other descent - you need to add air as you go down. If you're wearing a thick wetsuit then compression will lose buoyancy AND take away its warmth. The last 10m is where most changes are noticed due to the pressure laws.

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)

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You can't just plan a dive based on NDL time - it ignores gas consumption and so on. In my view here you should be planning on tables initially and limiting yourself to 5 mins on the bottom before ascending. Then SLOWLY building up to longer bottom times. Blindly relying on a computer is not a wise move at all.

You also need to know the dive site layout - is it a flat bottom at that depth? a wall? a sloping reef? All of this will affect how you conduct it. Other things to consider - in lots of parts ambient light at depth is much less than shallower, in some cases its completely dark so what about lights and backups? Will you be ascending up a fixed line or under an SMB or even swimming back to shallower water?

36m really isnt that deep but if you havent been there before it can seem it. Its RIGHT on the line as to what is worth doing as a no-stop dive and with no redundant air source over what i'd be prepared to do myself. For that i'd want twins to give a nice safety margin.