Rec Vs. Technical???

[Octopusprime]

I want to start out by saying I am a recreational diver NOT a tech diver but have some questions to see if a tech course is something I should pursue. I live in Illinois and do a lot of mid west diving. It seams that many of the things I find my self interested in going to see are in 100-140 ft in lake Michigan. However at 120ft only having 13 min of bottom time seams like a lot of work and time for 13 min of bottom time.

I have seen some OLD deco stop tables that im assuming are before nitrox/trimix etc and I am wondering what I would be getting my self into. I would assume I would go to Dual back gas + stage bottles which means loosing the BCD and going to a wing and back plate.

I guess my main question is lets say I was going to go to 120 ft and had a bottom time of 45-60 min. How many different gasses will I need and what would my deco stops and times be. I see a lot of guys in LM with Dual Back gas and 2 stage bottles, but have seen some with dual back gas and 4 stage bottles. I have heard of some CRAZY long deco stops and hanging on a rope for 60 min for a 60 min dive does not sound fun either. but I have heard with mixed gas those stops are much shorter.

can someone give a conservative example of a 120ft dive with 60 min bottom time?

 

[rivers]

You're looking at a pretty big dive.

Decompression model: ZHL16-B + GF


DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = GF 30/85


Dec to 120ft (2) Triox 25/25 50ft/min descent.
Level 120ft 57:36 (60) Triox 25/25 1.16 ppO2, 64ft ead, 82ft end
Asc to 70ft (61) Triox 25/25 -30ft/min ascent.
Asc to 60ft (62) Nitrox 50 -30ft/min ascent.
Stop at 60ft 1:00 (63) Nitrox 50 1.41 ppO2, 26ft ead
Stop at 50ft 2:00 (65) Nitrox 50 1.26 ppO2, 20ft ead
Stop at 40ft 3:00 (68) Nitrox 50 1.10 ppO2, 13ft ead
Stop at 30ft 6:00 (74) Nitrox 50 0.95 ppO2, 7ft ead
Stop at 20ft 33:00 (107) Nitrox 50 0.80 ppO2, 1ft ead
Surface (113) Nitrox 50 -3ft/min ascent.


OTU's this dive: 114
CNS Total: 40.1%


198.7 cu ft Triox 25/25
63.3 cu ft Nitrox 50
262 cu ft TOTAL

Most of my diving tends to blur the line between rec and tech. All of my diving at the moment is within the accepted recreational ranges, but if I'm in the sea, I tend to do a bit of deco. Normally it's back gas deco, as I haven't had a chance to use my shiny trimix ticket in the UK yet. A common dive for me is 45 minutes at 30m (100 feet), with 15 minutes of deco at 6, plus 1 minute stops at 15, 12, and 9. I tend to 35-40 minutes between 35-40m (depends on the dive, tides, and if I'm on a the club rib or not and others are waiting to splash). Deco depends what I'm doing.

 

[tbone1004]

sounds like you need the following
Nitrox course
Advanced Nitrox and deco procedures
Trimix 1

I'll play along and be nice though

You said 140ft, so we'll go with 136 for easy math, this is trimix territory for some people to curb narcosis, and really is rebreather territory, but here it is

136 is 4atm, 5ata
Using an approximate SAC rate of 1.0 which is usually used for planning, you need 5*1.0*60=300cf of gas. Cave filled Faber 112's at 3600psi will barely cut it. More likely solution would be 112's with either one or two of AL80 stage bottles with 28% nitrox in them as that is the best mix for a PO2 of 1.4. Stage bottles will be determined by how much extra gas you want to carry, for your buddy, I would carry one personally. One AL80 full of 100% O2

Profile is as follows using gf of 40/70

60 minutes at 136ffw on 28%
4 mins at 60 on 28%
6 mins at 50 on 28%
9 mins at 40 on 28%
17 mins at 30 on 28%
11 mins at 20 on 100%
21 mins at 10 on 100%
132 minutes total

this is a not a joke of a dive, and really will take you a long time to get to the point where you can safely perform these dives. Carrying a 50% mix like posted above will cut your deco time by a few minutes, but is an extra bottle to carry so probably not worth it, trimix is recommended at these depths but is very expensive, so I wouldn't bother using it personally but narcosis does not effect me as much as it does for some. If you're doing these dives regularly you can actually justify the $15k it would cost to switch to a rebreather because your deco stops will be cut shorter and you won't be wasting nearly as much gas which helps.

 

[Superlyte27]

Square Profile? Sawtooth? Computer? Tables?

---------- Post added February 1st, 2015 at 04:55 PM ----------

Yikes Rivers, what a terrible gas selection. No way would I do that dive that way.

---------- Post added February 1st, 2015 at 05:00 PM ----------

He said 120' for 60 minutes. On 30% Nitrox with 100% O2 for Deco, it's about 30 minutes of deco, depending on your GF. If you add some helium to the mix, it won't change your time much, but will give you a clearer head, probably.

 

[rivers]

Square Profile? Sawtooth? Computer? Tables?

---------- Post added February 1st, 2015 at 04:55 PM ----------

Yikes Rivers, what a terrible gas selection. No way would I do that dive that way.

I just picked an arbitrary gas. It's not one I would use either. Depending who I was diving with, I would use 21/35 (GUE standard gases and all that) for an extended time at 37m or if there was a possibility for deeper, or 30/30 (if conditions were going to be a bit difficult) or just plain 30% (if conditions were fine) if max depth was 37m, but most was spent around 33m or so . But I also wouldn't do an hour at 37m. It's a massive dive. I would cap it at 35-40 minutes max dive time. 21/35 I would have a deco gas, 30/30 or 30% i would use back gas.

 

[Octopusprime]

Square Profile? Sawtooth? Computer? Tables?

---------- Post added February 1st, 2015 at 04:55 PM ----------

Yikes Rivers, what a terrible gas selection. No way would I do that dive that way.


---------- Post added February 1st, 2015 at 05:00 PM ----------

He said 120' for 60 minutes. On 30% Nitrox with 100% O2 for Deco, it's about 30 minutes of deco, depending on your GF. If you add some helium to the mix, it won't change your time much, but will give you a clearer head, probably.

For simplicity lets assume square profile with a computer... maybe 60 min of bottom time is longer than I would do but lets keep it for simplicity.

Looks like the Back gas is used to descend and bottom time? then 2 mixes for accent?

---------- Post added February 1st, 2015 at 04:11 PM ----------

I'm less concerned with what the gas mixes are right now... I figure I would learn each mix in training... I know the mix will determine the stops but, It was more about to get that type of bottom time how many different mixes would I need and what would the stops look like.

---------- Post added February 1st, 2015 at 04:14 PM ----------

tbone, I already have nitrox and have been looking at what I will be taking this year. is trimex 1 the first of the tec courses?

---------- Post added February 1st, 2015 at 04:16 PM ----------

I just picked an arbitrary gas. It's not one I would use either. Depending who I was diving with, I would use 21/35 (GUE standard gases and all that) for an extended time at 37m or if there was a possibility for deeper, or 30/30 (if conditions were going to be a bit difficult) or just plain 30% (if conditions were fine) if max depth was 37m, but most was spent around 33m or so . But I also wouldn't do an hour at 37m. It's a massive dive. I would cap it at 35-40 minutes max dive time. 21/35 I would have a deco gas, 30/30 or 30% i would use back gas.

Wen you say "MAX DIVE TIME" is that Bottom time or total time from surface, decesnd, bottom time, deco time etc?

 

[rivers]

Wen you say "MAX DIVE TIME" is that Bottom time or total time from surface, decesnd, bottom time, deco time etc?

Surface to start of ascent

 

[CptTightPants21]

For tech course is an "intro to tech" (I think it is tec40 for PADI and intro for everyone else)
Then you take Advanced Nitrox and Deco Procedures which will allow you to do dives up to ~170 ft with options of deco gas all the way to 100%. You don't need trimix for the dives you are talking about.

Although I don't recommend it, a poor man's route (depending on depth and time) could be to start diving a HP130 and use it to extend bottom time slightly while giving enough gas to do a longer air deco. I know a few divers that use HP130 in the 110-120 ft range and don't bring any oxygen.

 

[tbone1004]

Trimix 1 is nowhere near the first, actually the last one for this type of diving, you'll likely have to take a tech fundamentals course to really learn how to dive in the configurations required for these types of dives, then an AN/DP course to teach full decompression. Trimix is optional on that depth, it will clear your head a bit at the cost of dollars of trimix, not needed but if you are prone to being narc'd it will help quite a bit.

Max Dive time does not include ascent, that's descent+bottom time.

Tech fundamentals with any good agency will include bp/w use, operation of doubles or sidemount, gas planning, and dive execution
AN/DP will get you trained to dive 50% deco mix if you want to use it though it isn't really necessary for this, and then full decompression using 100% O2. There's a lot of stuff that can go wrong on these types of dives so you really need to get training squared away before you try to stay down for any length of time, the equipment isn't cheap either.
Used prices
$500-$600 for doubles
$500-$600 for doubles regulators
$300/bottle for AL bottles with regulator and rigging
$300 for BP/W
Will need a drysuit for that type of diving, so $2000 there minimum with undergarments undergarments, you don't need an extra inflation bottle, but you'll need some good underwear if not a drysuit heater to do that long of a run time.

 

[ddmattos]

---------- Post added February 1st, 2015 at 04:14 PM ----------

[/COLOR]tbone, I already have nitrox and have been looking at what I will be taking this year. is trimex 1 the first of the tec courses?

Look at your PADI Nitrox cert. You are only qualified to use 40% Nitrox max. For tech (Advanced Nitrox), you would be qualified to use 100% O2 for accelerated deco.

Look at the DSAT or TDI website for the Tech course progression. Tech is something you don't want to take shortcuts.