82 replies to this topic

[TraceMalin]

Trace,

Thanks for your comments. I have a question for you. I asked the same of Geek, but he seems to have disappeared.

What kind of runtimes are you getting on those ocean dives?

I have a great deal of trouble imagining myself running out of gas with 2 AL80s on my back, and AL80 stage, and a 40cuft bottle of 50/50 in an hour. That's 240cuft of backgas. And it would make me less than 15# negative. Aluminum backplate (2#), 4hr can light (2.5#), and I'm still less than 20 pounds negative.

Why are you guys taking huge steel cylinders in the ocean? Do you really need 350+ cuft of gas for what you're doing?

Well, Perrone, as you probably know George Irvine III suggested that to "Do It Right" ocean divers should be wearing double AL80's and planning their dives with no more than 20 minutes of decompression since conditions at sea can change rapidly. I agree with this most of the time. I dive double AL80's in the ocean and I prefer a single deco gas because I have to carry it throughout the dive. I also dislike epic decompression. My idea of decompression is to be lying on a cot, drinking Gatorade and watching "Band Of Brothers" on TV while being paid $650.00 per day by the good folks at Stolt. But, since I'm not a saturation diver and I'm paying to decompress, I try to keep it short and sweet. As you know, in a cave environment I can drop bottles. I'll be leaving my O2 at 20 - 30 feet, my 50/50 at 70 - 80 feet, and my stage will get dropped after I use 1/3 of my gas. I'll dive on my back gas until I reach 1/3's, turn the dive and pick up my stage and continue until I reach my first deco gas, make the switch and then ascend on schedule switching to my final deco gas and surfacing. I'm also in fresh water and therefore heavier from a lift standpoint. But, when I mentioned some ocean dives require more gas, let's look at a couple of profiles:

This could be the gas plan for an Andrea Doria dive at 200 feet:

Off gassing starts at 139.5ft

OTU's this dive: 69
CNS Total: 33.7%

154.6 cu ft Triox 21/35
17.7 cu ft Nitrox 50
10.8 cu ft Oxygen
183.1 cu ft TOTAL

This could be the gas plan for a Britannic dive at 400 feet:

Off gassing starts at 302.3ft

OTU's this dive: 138
CNS Total: 72.7%

206.0 cu ft Trimix 9/57
43.2 cu ft Trimix 17/19
37.2 cu ft Nitrox 40
22.8 cu ft Nitrox 70
36.4 cu ft Oxygen
345.5 cu ft TOTAL

Since AL 80's only have an actual capacity of 154.8 cubic feet they would just allow you to make a 20 minute dive on the Andrea Doria with a run time of 48 minutes, but wouldn't allow you to make a 12 minute dive on the Britannic with a total run time of 107 minutes.

In the case of the Doria, I'd prefer moving to PST 104's which would offer 212.4 cubic feet of gas rather than dive AL 80's if I were going to make that dive.

The reason I'm in love with caves is that I'm process oriented. I like taking my time and being able to do something I love for 2 or 3 hours rather than just for 12 minutes!

~ Trace

[Geek]

Trace,

Thanks for your comments. I have a question for you. I asked the same of Geek, but he seems to have disappeared.

What kind of runtimes are you getting on those ocean dives?

I have a great deal of trouble imagining myself running out of gas with 2 AL80s on my back, and AL80 stage, and a 40cuft bottle of 50/50 in an hour. That's 240cuft of backgas. And it would make me less than 15# negative. Aluminum backplate (2#), 4hr can light (2.5#), and I'm still less than 20 pounds negative.

Why are you guys taking huge steel cylinders in the ocean? Do you really need 350+ cuft of gas for what you're doing?

Haven't disappeared, just busy.

First a comparison. Trace is a young fit guy, who probably has a wonderful SAC rate and can do long ocean dives. However, I am an old out of shape desk jockey with an SAC rate that stinks, so Trace is going to get much better run times than I. I am going to be doing much shorter dives. The conditions are also cold, low visibility, and often some amount of current. This is a stressful environment and everyone's SAC rate is likely to be worse than in a nice warm water, good vis, environment.

Back to the question of why the huge steel tanks. In my case I am slightly positive without the tanks, (due to a high fat to muscle ratio ) so using the steel tanks simultaneously provides more air for tanks of specific external dimensions (to compensate for the lousy SAC rate) and takes weight off the belt. For example, my HP 100s are almost exactly the same dimensions as AL80s, so if I were to switch to AL80s I would lose 40 cf of gas, and need to add 8 lbs of weight to my belt, making my rig both heavier on the surface and larger at the same time.

I also would not describe the tanks as huge. HP 100s are the tanks I see most often locally. They are about the size of an AL80 and are much more durable if properly cared for. You also get the extra 40 cf and the negative bouyancy is helpful unless you are in really terrific shape. (Thanks for bringing up that muscle to fat thing Trace. ) If you move to HP 120s, you get a slightly longer tank, which is nice if you're taller (I'm not) or would like to lose that AL80 stage you're dragging around.

To get a sense of conditions, take your existing SAC rate and add 0.2 for cold, stress, and workload. That's about the difference I experience between diving here and diving in FL. Assume you are following the rule of thirds and figure out what you would need for a wreck dive at 80 feet, 100 feet, or 120 feet. You'll have a decent idea of what your personal gas needs would be to dive in the NJ to LI area.

[ScubaDadMiami]

Trace,

Thanks for your comments. I have a question for you. I asked the same of Geek, but he seems to have disappeared.

What kind of runtimes are you getting on those ocean dives?

I have a great deal of trouble imagining myself running out of gas with 2 AL80s on my back, and AL80 stage, and a 40cuft bottle of 50/50 in an hour. That's 240cuft of backgas. And it would make me less than 15# negative. Aluminum backplate (2#), 4hr can light (2.5#), and I'm still less than 20 pounds negative.

Why are you guys taking huge steel cylinders in the ocean? Do you really need 350+ cuft of gas for what you're doing?

At 250 feet, with double 120s plus 40s of 50 percent and 100 percent oxygen, I was doing about 25 to 30 minutes on the bottom. Run times about 145 minutes or so. Staying inside the Rule of Thirds. This barely gave me enough gas to do the dive.

That's when I decided it was time for CCR. At those kinds of depths or deeper, the last thing I want is time pressure like that.

[PerroneFord]

Howard,

All bets are off below 200ft! It will be several years before I am there.

[Geek]

Trace,

Thanks for your comments. I have a question for you. I asked the same of Geek, but he seems to have disappeared.

What kind of runtimes are you getting on those ocean dives?

I have a great deal of trouble imagining myself running out of gas with 2 AL80s on my back, and AL80 stage, and a 40cuft bottle of 50/50 in an hour. That's 240cuft of backgas. And it would make me less than 15# negative. Aluminum backplate (2#), 4hr can light (2.5#), and I'm still less than 20 pounds negative.

Why are you guys taking huge steel cylinders in the ocean? Do you really need 350+ cuft of gas for what you're doing?

Well, Perrone, as you probably know George Irvine III suggested that to "Do It Right" ocean divers should be wearing double AL80's and planning their dives with no more than 20 minutes of decompression since conditions at sea can change rapidly. I agree with this most of the time. I dive double AL80's in the ocean and I prefer a single deco gas because I have to carry it throughout the dive. I also dislike epic decompression. My idea of decompression is to be lying on a cot, drinking Gatorade and watching "Band Of Brothers" on TV while being paid $650.00 per day by the good folks at Stolt. But, since I'm not a saturation diver and I'm paying to decompress, I try to keep it short and sweet. As you know, in a cave environment I can drop bottles. I'll be leaving my O2 at 20 - 30 feet, my 50/50 at 70 - 80 feet, and my stage will get dropped after I use 1/3 of my gas. I'll dive on my back gas until I reach 1/3's, turn the dive and pick up my stage and continue until I reach my first deco gas, make the switch and then ascend on schedule switching to my final deco gas and surfacing. I'm also in fresh water and therefore heavier from a lift standpoint. But, when I mentioned some ocean dives require more gas, let's look at a couple of profiles:

This could be the gas plan for an Andrea Doria dive at 200 feet:

Off gassing starts at 139.5ft

OTU's this dive: 69
CNS Total: 33.7%

154.6 cu ft Triox 21/35
17.7 cu ft Nitrox 50
10.8 cu ft Oxygen
183.1 cu ft TOTAL

This could be the gas plan for a Britannic dive at 400 feet:

Off gassing starts at 302.3ft

OTU's this dive: 138
CNS Total: 72.7%

206.0 cu ft Trimix 9/57
43.2 cu ft Trimix 17/19
37.2 cu ft Nitrox 40
22.8 cu ft Nitrox 70
36.4 cu ft Oxygen
345.5 cu ft TOTAL

Since AL 80's only have an actual capacity of 154.8 cubic feet they would just allow you to make a 20 minute dive on the Andrea Doria with a run time of 48 minutes, but wouldn't allow you to make a 12 minute dive on the Britannic with a total run time of 107 minutes.

In the case of the Doria, I'd prefer moving to PST 104's which would offer 212.4 cubic feet of gas rather than dive AL 80's if I were going to make that dive.

The reason I'm in love with caves is that I'm process oriented. I like taking my time and being able to do something I love for 2 or 3 hours rather than just for 12 minutes!

~ Trace

Good thing I don't intend to dive either of those wrecks!

[TraceMalin]

Howard,

All bets are off below 200ft! It will be several years before I am there.

You're disappointing the dive centers who are told to encourage prospective open water students to "start today" with technical training.

Good job!

~ Trace

[PerroneFord]

Trace, Ginnie Cavern and Devils is PLENTY technical for me! The Oriskany next weekend is going to be technical. I'm taking doubles!

[Dive_Girl]

You're disappointing the dive centers who are told to encourage prospective open water students to "start today" with technical training.

What? You've seen the new banner at our shop???

[Diverbrian]

DiverBrian,

A couple of questions if I may...

1. Why are you diving thirds in the great lakes? It would seem that you could easily get away with halves unless you are penetrating wrecks. Maybe you are.

2. You are taking 200-260cuft of gas. My Double 80s with a stage is 240cuft (well closer to 230, but still). It's close

3. You are doing 2 gas switches. I guess if I had 200ft dives planned, I would too. Right now, I am going to be looking at 150ft dives max for a while.

4. You don't carry enough backgas to deco on it? Seems that lost gas planning would dictate it, unless you plan on buddy breathing with your buddy on the stops. If you lose the 50% bottle, you're not just going to blow off everything until you get to 20ft are you?

Thanks for your response.

To clarify my point, I am talking 20-30 minutes bottom time at 150-200 ft. There is significant deco involved with that. The reason for that is that the tech charters still don't have room for two sets of doubles up here or the time for the two hour or better surface interval to allow for a second dive. The conditions on the Lakes change such being out on a dive site for much more than a few hours can be unsafe. So, for a tech charter is one dive and the boat heads back in for more money than two more shallow (and closer in) dives on a recreational charter. I like to get the best bang for my buck.

I use two deco gases at times to account for the fact that I may not have one of my deco gases. For these kind of deep dives backgas deco is not always possible. So, I have an added cushion. So yes, I am compensating for the fact that I can't carry larger doubles with the added amount of deco gas to do my deco. And yes, I do some wreck penetration as well. Either the deco requirement or the wreck penetration requires rule of thirds. Remember the deco obligation is an overhead. And yes, I do plan to account for losing the EAN50 and have enough to get to 20 ft. But without a deco gas, the deco hang at 20 ft. is too long for my back gas to reliably get me out of the water if I were to try that. Even though I do deeper stops, most of my deco is at 20 and 15 ft. on these profiles.

As Geek points out, I am not in Trace's condition. I am in decent shape, but I do use more breathing gas than someone like Trace who is in phenominal shape. I am in Geek's camp in another aspect, if I have to carry the weight (due to the added insulation required in cold water), I might as well make in the form of something that gives me more of what I need (like breathing gas) than in the form of lead, which is useless.

Most of the divers that I dive with are using LP95's to LP121's pumped up to about 3000 psi. I am one of the few holdouts with the HP tanks. Many are using one deco gas. I think that is fine for them, but I still want my deco gases with me in the event that I get blown from the wreck or lose the mooring line (remember mooring lines have been known to break).

[TraceMalin]

You're disappointing the dive centers who are told to encourage prospective open water students to "start today" with technical training.

What? You've seen the new banner at our shop???

Please tell me that was a joke!

~ Trace

[peterbj7]

This could be the gas plan for a Britannic dive at 400 feet:

Off gassing starts at 302.3ft

OTU's this dive: 138
CNS Total: 72.7%

206.0 cu ft Trimix 9/57
43.2 cu ft Trimix 17/19
37.2 cu ft Nitrox 40
22.8 cu ft Nitrox 70
36.4 cu ft Oxygen
345.5 cu ft TOTAL

Since AL 80's only have an actual capacity of 154.8 cubic feet they would just allow you to make a 20 minute dive on the Andrea Doria with a run time of 48 minutes, but wouldn't allow you to make a 12 minute dive on the Britannic with a total run time of 107 minutes.

In the case of the Doria, I'd prefer moving to PST 104's which would offer 212.4 cubic feet of gas rather than dive AL 80's if I were going to make that dive.

The reason I'm in love with caves is that I'm process oriented. I like taking my time and being able to do something I love for 2 or 3 hours rather than just for 12 minutes!

~ Trace

Have you dived the Britannic, Trace?

[TraceMalin]

Have you dived the Britannic, Trace?

No, I haven't. I would love to explore that wreck though someday; especially because it's off Greece. My GUE instructors Andrew Georgitsis and Bob Sherwood dove the Britannic when GUE did the documentary for either the History Channel or the Discovery Channel.

For an example of why divers would require large capacity cylinders for ocean diving, I used the gas plan of Nick Hope's 1998 Britannic expedition to demonstrate for Perrone a possible extreme open circuit dive.

Have you done it, Peter?

~ Trace

[PerroneFord]

Trace, do you remember what the dive profiles looked like at WKPP pre-RB80?

Clearly, I understand needing large steel cylinders for long exposures, but come on.. why take 130s to do a 45 minute dive at 130ft?

[Diverbrian]

Trace, do you remember what the dive profiles looked like at WKPP pre-RB80?

Clearly, I understand needing large steel cylinders for long exposures, but come on.. why take 130s to do a 45 minute dive at 130ft?

Because I have them and I don't feel like maintaining yet another set of doubles. I already have two sets that need to be visualed and O2 cleaned once per year. The larger ones are useful for everything and the smaller ones are only useful for shallower dives of which I do less often now and plan to do even less in the future.

As well, the 130's or 100's are good for a couple of dives down to 130 with light deco. Lower than that, I would run a little lower on gas than I would like trying to do two relatively deep dives.

Think about this, no diver ever died from having too much breathing gas. Most of the time they died from not having enough breathing gas.

[Geek]

Trace, do you remember what the dive profiles looked like at WKPP pre-RB80?

Clearly, I understand needing large steel cylinders for long exposures, but come on.. why take 130s to do a 45 minute dive at 130ft?

With a working SAC of 0.8 and a resting SAC of 0.5, Air for bottom gas and Nitrox 50 for deco, V-Planner calculates 180 cf of backgas and 38 cf of deco gas. Using rule of thirds tells me I need 270 cf of backgas. Doubled 130s sounds pretty close. Am I missing something here?