What would you do?

[drbill]

Geoff... IMHO deco diving isn't all that complicated as long as it doesn't involved mixed gasses and gas changes. Read up on it. My concern regarding the 45 m (almost 150 ft) dive would be your suspectibility to narcosis and how that could affect the dive and your response to it. I've dived many times to 200 ft on air without problems, but that was with several months of acclimitization to depth and narcosis. Then I stopped doing such dives because I'd achieved what I needed to with them. A year later I tried a dive to 150 fsw and was as narced as I'd ever been because my body had little tolerance after a year of much shallower diving. It might be best to skip that deep dive and just enjoy the rest of the ones you feel comfortable doing.

 

[tomfcrist]

Bill, the issue is not carrying all the gas he needs on his person. Prestaged tanks works fine in caves, but not so much in OW. What if he doesn't find the staged tanks? What if he needs to make a free ascent? The answer is that he won't have the gas supply to do his deco, which by the way he has no knowledge of how to do anyway. This WILL lead to a post by DandyDon...

 

[TSandM]

I wouldn't do this -- I'd do the shallow dives.

Here's why: At 45m, you're at 5.5 ATA. Given a good SAC rate (say, 0.5, which is on the good side for an adult male), you're using close to 3 cfm of gas. Now assume you are at your further point from the anchor line, and you have a reg freeflow, which although not a frequent malfunction, is a very conceivable one. Your tank will be empty in under 90 seconds. Does anybody down there with you have enough gas to get you to the hang bottles? Assuming you have staged deco tanks at 70 feet (unlikely, in an operation that is doing air deco), it's going to take almost 40 cubic feet of gas to get you and your buddy there, using an appropriate ascent strategy for a staged decompression dive to that depth. That's OVER HALF the tank you took down with you -- does your buddy have that much gas left? And that "rock bottom" calculation assumes a direct ascent, without a return to the anchor line at 45 m . . .

Everything goes well, until it doesn't. I don't ever want to put myself deliberately in a situation where a single major malfunction is not salvageable.

And I don't think 10 minute bottom times on wrecks where you can't do your deco up a wall are much fun, either.

 

[scububa]

I agree there are several additional things to consider above running a deco table. What happens if something goes wrong? What if you have to help someone else? What margins do you have? What about making someone else help you and eating up their margins? Sounds like you'd have no redundancy. Are you diving with a trusted buddy that you know works as a team for this? You don't need doubles, but you could take a stage strap setup and regulator and sling a 2nd 80AL. But, you should have practice handling it and knowing what your gas margins are. If you are diving solo, you don't have to account for getting another diver back (or he you), otherwise you need to factor that.

Narcosis, lack of redundancy and not knowing what to do if the plan gets derailed are the things that would bother me.

I can't come up from 140 ft on a single breath, so I don't put myself in that situation. If I am diving below 70 ft. I want another air supply with me (doubles or stage). When I was first diving, I did plenty of rec dives below 90 feet with a single tank. The thought of that now makes my skin crawl. Part of that is I have now seen plenty of stuff happen to gear on a dive. It sure is nice to be able to switch over and deal with it on a relaxed basis. That wouldn't be the case if it was my only air source.

The bottom line is you should consider and understand the risks. If the event is important enough to justify the risks, then you do the dive.

 

[Foxfish]

And the link you provided in the OP gives the depth as 50 m. Do you penetrate the wrecks?

 

[SeaHorse81]

Personally, I would stick to the dives that fit what I'm used to. I have never done any decompression diving and that is because of thoughtful choice -- I don't want to, because there's nothing deco diving has to offer me that is worth (to me) the increased risks. The fact of someone else picking up the tab doesn't change what I have decided is right for me.

 

[Soakedlontra]

I wouldn't do it unless I have the necessary equipment, proper training and built up enough experience in planning and performing these type of dives with confidence first. Don't let peer pressure make you gloss over the risks involved in doing such dives without the proper training, experience and just one A 80 cylinder.

Even if you get the training etc. before your departure, it sounds like that you will be stuck with one A 80 unless you can arrange to have two side mounted cylinders. I would keep it simple and enjoy the shallow dives.

A while ago I dove a wreck in Roatan that was 110 ft. deep. I decided to go to that depth because my buddy and I were able to rent A 120 tanks. All the other divers had A 80s. Toward the end of the dive we were back on the reef again and saw a diver sharing air with the dive master because he was low on air. Fortunately nothing happened during the deepest part of the dive.

 

[Hatul]

I wouldn't do this -- I'd do the shallow dives.

Here's why: At 45m, you're at 5.5 ATA. Given a good SAC rate (say, 0.5, which is on the good side for an adult male), you're using close to 3 cfm of gas. Now assume you are at your further point from the anchor line, and you have a reg freeflow, which although not a frequent malfunction, is a very conceivable one. Your tank will be empty in under 90 seconds. Does anybody down there with you have enough gas to get you to the hang bottles? Assuming you have staged deco tanks at 70 feet (unlikely, in an operation that is doing air deco), it's going to take almost 40 cubic feet of gas to get you and your buddy there, using an appropriate ascent strategy for a staged decompression dive to that depth. That's OVER HALF the tank you took down with you -- does your buddy have that much gas left? And that "rock bottom" calculation assumes a direct ascent, without a return to the anchor line at 45 m . . .

Everything goes well, until it doesn't. I don't ever want to put myself deliberately in a situation where a single major malfunction is not salvageable.

And I don't think 10 minute bottom times on wrecks where you can't do your deco up a wall are much fun, either.

To deal with unlikely failures like this I'd take a 19 cu ft pony, which will get you to the deco bottles. Besides the 45 m was listed as a maximum and you can always stay shallower.

 

[tomfcrist]

I wouldn't do this -- I'd do the shallow dives.

Here's why: At 45m, you're at 5.5 ATA. Given a good SAC rate (say, 0.5, which is on the good side for an adult male), you're using close to 3 cfm of gas. Now assume you are at your further point from the anchor line, and you have a reg freeflow, which although not a frequent malfunction, is a very conceivable one. Your tank will be empty in under 90 seconds. Does anybody down there with you have enough gas to get you to the hang bottles? Assuming you have staged deco tanks at 70 feet (unlikely, in an operation that is doing air deco), it's going to take almost 40 cubic feet of gas to get you and your buddy there, using an appropriate ascent strategy for a staged decompression dive to that depth. That's OVER HALF the tank you took down with you -- does your buddy have that much gas left? And that "rock bottom" calculation assumes a direct ascent, without a return to the anchor line at 45 m . . .

Everything goes well, until it doesn't. I don't ever want to put myself deliberately in a situation where a single major malfunction is not salvageable.

And I don't think 10 minute bottom times on wrecks where you can't do your deco up a wall are much fun, either.

To deal with unlikely failures like this I'd take a 19 cu ft pony, which will get you to the deco bottles. Besides the 45 m was listed as a maximum and you can always stay shallower.

What? Why on earth would you risk stationary staged deco bottles in OW? Want to know what happens when you do that???? Read about the Rouses. Or the many others whom made the same dumb choice.

 

[geoff w]

Nowhere in there is he asking advise as to what he should do, he wants to know what someone else would do. So I told him. I didn’t say he should, nor did I say he should get training; why? Because he didn’t ask for advise; he was taking a poll.

A rudimentary understanding of deco theory and a set of navy air dive tables is all that is needed to plan and execute the dives the OP is describing. Or as Akimbo posted "It isn't rocket science, study up a little, and have fun".

Quite possibly the most on target answer to my original question! Thank you! Not really any surprises in the answers. Either [a] I do all the deco procedure training or I'll be a statistic and die (I forgot to mention split fins and AIR-2, so I'm a goner anyway), or it's old school deco diving and I'll get narced so pay attention but certainly doable.

... This trip may seem like a once in a lifetime opportunity that warrants pushing the envelope, but if it is something that really attracts you I'm sure you can find a way to go back there and dive it "by the book."

This location was never on my bucket list, and definitely not once in a lifetime (unless I die doing the dives) but having a friend foot part of the bill and the way she raved about the diving piqued my interest. The number one consideration in our minds for PNG is having to take antimalarial prophylactics before, during and after; when we took those for the San Blas islands off Panama (really pristine diving, by the way), we really felt like crap. We haven't even decided to go; we're still formulating opinions, weighing options and considering pland and alternatives

Yes tourist destinations have doubles...bioniare, key largo, etc all have ops whom teach tech. If back mounted doubles aren't available, go side mount.

The advise you have been given is sound....but if you choose to go and dive deco blindly, that is your prerogative. If you are as niece about the possible issues with the type of dive you have described as I think you are, I will be anxiously awaiting dandy dons post in A&I sometime during your trip.

Too bad I'm not going to any of those places you mentioned :headscratch: I'm bringing my own gear, which could do backmounted doubles, but getting trained and suitably proficient in doubles for a single day of diving isn't in the plans right now. I'd never consider something like this with rental gear

No mention of Tufi in the A&I forum, although a search for "Coolidge" did provide some good reading

Geoff... IMHO deco diving isn't all that complicated as long as it doesn't involved mixed gasses and gas changes. Read up on it. My concern regarding the 45 m (almost 150 ft) dive would be your suspectibility to narcosis and how that could affect the dive and your response to it. I've dived many times to 200 ft on air without problems, but that was with several months of acclimitization to depth and narcosis. Then I stopped doing such dives because I'd achieved what I needed to with them. A year later I tried a dive to 150 fsw and was as narced as I'd ever been because my body had little tolerance after a year of much shallower diving. It might be best to skip that deep dive and just enjoy the rest of the ones you feel comfortable doing.

Dr Bill - as always, insightful and thoughtful experience to answer a question Tolerance to getting narced is probably the biggest obstacle to overcome initially. I need to contact my friends / hosts who are so keen on going back to Tufi to find out more about their experiences there before. She's loopy to begin with, so not sure what she'll be like that deep!

Bill, the issue is not carrying all the gas he needs on his person. Prestaged tanks works fine in caves, but not so much in OW. What if he doesn't find the staged tanks? What if he needs to make a free ascent? The answer is that he won't have the gas supply to do his deco, which by the way he has no knowledge of how to do anyway. This WILL lead to a post by DandyDon...

If I can't find staged tanks, I've got a much bigger problem. 100+ ft viz on a guided and tightly controlled / highly structured dive with an ascent line and tanks hanging down from the surface.

I wouldn't do this -- I'd do the shallow dives.

Here's why: At 45m, you're at 5.5 ATA. Given a good SAC rate (say, 0.5, which is on the good side for an adult male), you're using close to 3 cfm of gas. Now assume you are at your further point from the anchor line, and you have a reg freeflow, which although not a frequent malfunction, is a very conceivable one. Your tank will be empty in under 90 seconds. Does anybody down there with you have enough gas to get you to the hang bottles? Assuming you have staged deco tanks at 70 feet (unlikely, in an operation that is doing air deco), it's going to take almost 40 cubic feet of gas to get you and your buddy there, using an appropriate ascent strategy for a staged decompression dive to that depth. That's OVER HALF the tank you took down with you -- does your buddy have that much gas left? And that "rock bottom" calculation assumes a direct ascent, without a return to the anchor line at 45 m . . .

Everything goes well, until it doesn't. I don't ever want to put myself deliberately in a situation where a single major malfunction is not salvageable.

And I don't think 10 minute bottom times on wrecks where you can't do your deco up a wall are much fun, either.

Without a doubt the most rational explanation of what can go wrong (besides getting narced and/or bent). Thank you for the example! One of my neighbors / dive buddies is a very accomplished tech diver, pre-GUE and pre-TDI having figured out a lot of technique and equipment himself. Hearing him talk about several hours for mid-water water deco stops never made it sound very appealing, even for the occasional dolphin that swims by to check you out.

I agree there are several additional things to consider above running a deco table. What happens if something goes wrong? What if you have to help someone else? What margins do you have? What about making someone else help you and eating up their margins? Sounds like you'd have no redundancy. Are you diving with a trusted buddy that you know works as a team for this? You don't need doubles, but you could take a stage strap setup and regulator and sling a 2nd 80AL. But, you should have practice handling it and knowing what your gas margins are. If you are diving solo, you don't have to account for getting another diver back (or he you), otherwise you need to factor that.

Narcosis, lack of redundancy and not knowing what to do if the plan gets derailed are the things that would bother me.

I can't come up from 140 ft on a single breath, so I don't put myself in that situation. If I am diving below 70 ft. I want another air supply with me (doubles or stage). When I was first diving, I did plenty of rec dives below 90 feet with a single tank. The thought of that now makes my skin crawl. Part of that is I have now seen plenty of stuff happen to gear on a dive. It sure is nice to be able to switch over and deal with it on a relaxed basis. That wouldn't be the case if it was my only air source.

The bottom line is you should consider and understand the risks. If the event is important enough to justify the risks, then you do the dive.

Good points, but for the most part applicable to any dive, even a casual weekend beach dive with regular buddies. Planning for multiple levels of contingencies is always an ongoing part of any dive (or at least should be)

Most recreational wreck dives over 90 ft in So Cal (note I said recreational) are typically done the by majority with either a single 80 or 100 cu ft tank, as well as into the several submarine canyons that come close to shore. Pretty much all tourist diving around Hawaii in the 70-130 ft range is with Al80s. I think I understand the risks associated with these dives, and choose which ones to do or not (and yes, I will dive that deep with a single 80 cu ft tank, but plan accordingly; all dives are within limits of my training and standards of recreational scuba certification agencies). Diving past 130 ft and incurring a deco obligation is outside the realm of recreational diving training and certification, and my training, but people still do it. Hence my original question

Personally, I would stick to the dives that fit what I'm used to. I have never done any decompression diving and that is because of thoughtful choice -- I don't want to, because there's nothing deco diving has to offer me that is worth (to me) the increased risks. The fact of someone else picking up the tab doesn't change what I have decided is right for me.

Precisely my statement up front that I have absolutely zero intention of becoming a technical diver. However, for a deco dive geared toward recreational divers with no technical training or certification, that's why I asked the question. Technically, every dive is a decompression dive; shoot to the surface too quickly from 100 feet without a slow ascent, safety stop(s), etc and risk the consequences! Even in OW training, divers are taught to do things that are in effect decompression, although there is no hard ceiling as for the dives I'm asking about here

I wouldn't do it unless I have the necessary equipment, proper training and built up enough experience in planning and performing these type of dives with confidence first. Don't let peer pressure make you gloss over the risks involved in doing such dives without the proper training, experience and just one A 80 cylinder.

Even if you get the training etc. before your departure, it sounds like that you will be stuck with one A 80 unless you can arrange to have two side mounted cylinders. I would keep it simple and enjoy the shallow dives.

A while ago I dove a wreck in Roatan that was 110 ft. deep. I decided to go to that depth because my buddy and I were able to rent A 120 tanks. All the other divers had A 80s. Toward the end of the dive we were back on the reef again and saw a diver sharing air with the dive master because he was low on air. Fortunately nothing happened during the deepest part of the dive.

No peer pressure for this, and I'm definitely not glossing over the risks. Yes, at most resorts, or at least every one I've been to, divers are limited to just one Al80 cylinder. I can't imagine anything bigger for recreational diving, because I always start running up against NDL time or getting cold or the rest of the group starts going up before running low on air, but that's all part of basic recreational diving gas management too. When I dive local wrecks here in the 90-120 ft range with a HP80, even on a suitable nitrox mix for the depth, my Suunto computer keeps bumping up against NDL time as the limiting factor for the dive. I'm not always happy about that, but I understand the options and choose to stay within the conservative gas model built into my particular computer. As TSandM pointed out, breathing gas disappears faster at 45m than recreational depths