Is this a Bad Dive Plan for Cozumel?

[Doc Harry]

Perhaps I should have said that deco diving for recreational divers is prohibited.

American Caving Accidents
http://www.karstportal.org/FileStorage/NSS_news/2011-v069-013.pdf

 

[gasgirl]

I would dive with you any time gasgirl (in spite of that ummmmm gas problem you apparently have) ...

Phew! Thanks for that, cbm32! I feel my SAC rate dropping.

I felt so rejected when DandyDon said he wouldn't buddy with me!!!

---------- Post Merged at 01:08 PM ---------- Previous Post was at 12:42 PM ----------

Wow, what a fantastic amount of utter tosh this thread has generated...

I've done thousands of dives with a variety of Suunto computers, along with, on occasion, Aladdins, VR3s and Uwatecs. Most of the recreational diving we do here is air to around 100-120 feet max depth, multi-level profile running to between 50 and 60 minutes, 90 minute SI, then repeat. Never had a problem using a Suunto D6, a Gekko (or a Zoop, which is the same computer), or a Vyper.

The answer to your question is to refuse to dive with anyone who expects you to dive 30 minutes after a 100 foot dive. That simple. DMs/guides who say 'Suuntos are rubbish, they're too conservative' are ACTUALLY saying 'I don't give a rat's ass about your safety, but I do want to get home and get rid of you tourists as early as possible'. They probably also think that diving 'aggressive' profiles makes them more manly in some way.

Yes, sometimes, if you jump in for a second dive after a short SI, a Suunto computer will reduce your no-deco time. It will also reduce your no-deco time if you ascend too fast. And if you do put it into deco on a first dive, just watch the time-to-surface rack up if you put it in deco again on the second dive!

If you don't have a clear understanding of what you're doing, I'd strongly recommend NOT putting your computer into deco. Unless someone is leading you on a fairly marginal profile, there should be absolutely no need anyway.

Well, I have to disagree that this thread is "utter tosh" (BTW, I had to look up the definition).

I believe I have a legitimate concern about "marginal profiles" in Cozumel based on several posts I have found on this forum. Although, there have been others who seem to think the short SI never happens, here is a reply from BradJ to a 2004 thread originally started by DandyDon describing why he ended up with a 18 min deco obigation on his Suunto:

Well it was typical Cozumel two tank diving: the first dive on a wall to around 100' for about 30 minutes, a short SI and then a fairly shallow second dive for 30-40 minutes.
The only thing that changed was the DM wanted to do Chankanab which is pretty shallow but the rest of the group wanted to do that wreck the U-???. I thought the DM was a little uncomfortable about the second dive but once in the water that wasn't the case.
That wreck is pretty deep, about 80' at the bottom. I thought we would hang out on the deck which is about 60' or so but he led everyone down near the bottom where we spent some time. About 20 minutes or so into the dive still at about 80' I realized the Vyper was almost out of NDL time. I figured the DM would plan for this and we would begin our ascent.
Much to my surprise he started to penetrate the wreck for another 5 minutes or more. I'm watching the DECO minutes start to build with the rest of the group and the DM seemingly oblivious.
Well finally we separate from the wreck and start drifting with the current, but everyone still stays near the bottom. I slowly begin ascending as the group gets smaller and smaller until I'm at 10' where the Vyper wants me and begin my 18 minute stop.
The amazing thing is a group finally does ascend but blows past me without even a SS. The DM and the rest of the group join me for their SS and a few minutes later he gives the thumbs-up. I shake my head and show him the Vyper which still has double digit DECO left. He tries to grab the others in the group but they're already at the surface.
The two of us hang out together until the Vyper clears and surface. The DM didn't want to talk about it back on the boat and the rest of the group had no clue what was going on. I did look at one guys Cobra and it was in Err mode.
I think DMs, especially in the Caribbean do the same dives every day and don't really worry about seemingly small changes in dive plans. And who knows, maybe the Vyper was way too conservative.

BradJ also posts in this thread:

"I came within a minute or two of entering DECO diving in Grand Cayman once. My dive buddy was also using a Vyper and his did enter DECO and locked him out (Err mode) when he didn't do a stop.
So two major diving destinations and two respected dive operators (Bob Soto's in Cayman) resulted in essentially unplanned decompression diving.
My question is are Suuntos too conservative or are these dives going too far.
I consider myself a fairly conservative diver. I always dive less aggressive than the DM, I'm usually more shallow than the rest of the group and I ascend very slowly."

BradJ sounds like someone I would dive with and he is only one of many members on this board who has posted this type of issue of unplanned decompression diving. Although, it would be great to say in black and white don't do it, I want to get some feedback on what to do if it happens to me on this Cozumel trip.

I have already gotten some good advice on this thread on how to pre-empt this if I can, AND how to react appropriately if it happens, AND I now better understand why it is a bad idea to rely on a computer for deco dive planning.

Thanks again to everyone for your helpful responses!

 

[TSandM]

I've already weighed in on the dive plan, but I also wanted to say that, when we dove in Cozumel, the boat tracked us pretty closely. If someone had to go up early, they just shot a bag and ascended, and the boat picked them up.

 

[-hh]

Attention: I am seeking opinions from divers who have first hand experience with Suunto computers only please! (For those who do not dive with Suuntos and do not know about the problems with the over-conservative algorithms that penalize repetitive dives with short surface intervals, please refrain from responding with non-productive critical comments!)

I've had a Suunto Vyper for ... well, a decent number of years now. It replaced a US Divers Monitor-I, for those who remember those, and in my side-by-side testing, I did find the Suunto to be clearly more conservative, even with the Suunto on its most "liberal" settings.

Brief background:
Shortly after purchasing my Suunto Cobra, I recall being advised by an instructor in Grand Cayman that it would be fine to incur a deco obligation at depth up to 10 minutes as it would clear during my multi-level profile as I ascended and did my safety stop. I opted not to voluntarily put my new computer into deco on that trip but I was diving in conditions and sites that easily allowed me to modify my depth to be shallower that the rest of the group.

I don't think I'd do 10 minutes of indicated obligation with my Vyper ... "casually". Sure, you can have some of an indicated obligation disappear on a multi-level profile, but (at least for my profiles) I find that they usually don't go down (or go away) all that much. Further, once one does get to your deco stop, there won't be a 1:1 correlation on the timer's countdown unless you hug right up to 10.1 fsw depth ...there's few things more disconcerting than doing ten minutes at 16fsw and noticing that the deco time only went down by 2 or 3 minutes...and still is saying that there's 15 more to go....hmmm. Thus said, when I do get a hard ceiling on the computer, I will pull a good ~20ft stop for 3-5 minutes before coming up to clear the indicated stop.

Shortly after that, I switched to diving Nitrox, and I no longer came even close to my NDL times on my repetiitve dives, and so I never had issues with Suunto being too conservative even when we were doing five dives a day (albeit with longer surface intervals than 60 minutes) on any of our subsequent dive trips.

I tend to find that they can start to get pretty cranky after ~2 days of dives on air, or ~4 days of an air/nitrox mix, or ~6 days of all nitrox tanks. For days of just 2-tank AM dives, the clue seems to be the second or third day after the computer didn't reset back to "Dive 1" for the first dive of the day...that seems to be the indicator of when it is starting to carry (and penalize for, probably) long compartments.

Because of conditions specific to Cozumel (ie. swim throughs at depth and possible strong currents), I am anticipating that the first dive of the day in Cozumel may be at a depth greater than the MOD for EAN 32% so we were planning on diving air. Then we are assuming that there will be a very short 30 minute surface interval before the second dive, so we are planning to dive wither EAN 32% or EAN 36% to help extend our NDL time for this second dive. However, my understanding is that Suuntos really impose serious penalties on the NDL's for surface intervals shorter than 60 minutes.

I've not heard "60 minutes" as a magic number for Suuntos before. Interesting. In any case, I'd be somewhat surprised if with a FIFO dive plan if the interval really is as short as this...and you can manipulate this factor some, by encouraging your diveboat's group to arrive early (get out early)...it isn't uncommon for the "time to start the second dive" to be based partly on the time of day, so an early start can reduce the temptation.

In any case, a two-tank day of Air+Nitrox can work out pretty well.

My questions for Nitrox divers in Cozumel are:
1. Do people commonly dive air on the first tank and then EAN on the second tank in Cozumel? ie. Will using EAN give us a more reasonable NDL on this second dive?
2. Is yes, would you recommend diving EAN 32% or 36% giving the typical second dive profiles in Cozumel?
3. Is anyone aware of oxygen toxicity problems diving with Nitrox on the first deep dive?

1. I've not dived Coz, but an (Air+32%) has become a pretty common pattern for my diving in the Caymans.

2. 36% would be nice for a second dive ... if the Brac had that mix available, I'd probably use it half the time on second dives.

3. I set my Suunto's alarm at 1.5 PPO2, which for 32% is a MOD of roughly 120fsw, which is "good enough" for most of my planned profiles. The differences in max exposure limits between 1.4 (150 minutes) and 1.5 (120 minutes) isn't anywhere near as significant as 1.6 (45 min), for those who want an operating margin.

My questions for those familiar with Suunto computers are :
1. Would you allow the Suunto computer to go into deco and assume it will clear as you slowly ascend (10 ft/min) with mulitlevel stops for several minutes at 50 and 40 and 30 feet?
2. If yes, what is the maximum deco obligation that you would incur (assuming, of course, that this still falls within the gas plan)?

1. Generally, I don't find much reason to "allow" it to go in.
2. ~7 minutes if I expect to be at my safety stop with 1100psi. That's 1 minute for error on the indicated stop time 500psi for the ~10 minutes running at 13fsw to see about getting the (4+1 error) minutes to clear without going to 10.01fsw, then 100psi at 10.1fsw for the 36 breaths it will take me for the standard 3 minute safety stop & back onboard still with 500psi. As you can see, I don't really trust the Suunto's claimed deco runtimes for when one is at 15fsw instead of 10.


-hh

 

[gasgirl]

Thanks for sharing your experience -hh and taking the time to answer my questions.

Here was a response from DandyDon to BradJ in that 2004 thread:

"Brad's experiences in Cozumel and a few others mentioned here point out many of the problems I'm wondering about...

(1) I don't know that I've ever seen a DM wear a computer in the Caribbean, and I've been around a bit.

(2) I have seen Caribbean DMs dive what I thought were excessive profiles, and customer divers without computers follow them in trust. DMs on my Devils Throat dive were all using 32% Nitrox to avoid DCS, but then they went below the 1.6 bottom! Just because a DM does it, especially outside of the U.S., doesn't make it safe.

(3) When a Computer goes into deco, the wearer doesn't know what it means for sure, and/or what to do about it."

Since I have not been diving in Cozumel, I am just trying to be proactive - ie. posing questions to see what I can learn ahead of time to deal wtih these types of scenarios if they come up on my trip.

I was pretty clear in my OP that I was making assumptions of anticipating some bad dive plans - based on what I had read re: other people's trips to Cozumel - but there are enough posts that I want to be prepared if it happens.

I have also posed questions to get feedback on posts that seemed specific to Suunto computers - that were made by other members - to clarify whether they were actually valid statements.

I have definitely learned a lot from the responses but I do feel that I am being judged for just asking these questions.

Maybe people are misinterpreting from the title of this thread that this is the way I am intentionally planning to dive in Cozumel?

Let me be clear that my intention is to dive safely in Cozumel.

If I had it to do over, would I post this thread again - yes, because of responses like the one from -hh!!!

 

[iluvcozumel]

I have been diving a Suunto Vyper for over 8 years, have over 100 dives in Cozumel and have been to around 130'. In the early days with the Suunto I did miss a NDL by a couple of minutes and was penalized by the computer with a 10 minute safety stop. After that incident, I always watch the NDL on second, third and fourth dives of the day and never really have any problems. Just move up 10 or so feet and you gain a lot of ND time. As far as Nitrox, 32% is fine for a first dive except on dive sites like Devils Throat. You can easily stay above the MOD on most other sites. As has been stated, if your operator doesn't do at least a 1 hour SI, find a new op. Less than 1 hour after any dive is just not safe. Especially when you are diving multiple days. And if the op is a good safety minded operation, they will not and should not let you dive a computer that is "locked out" because of a NDL error!!! Always dive conservatively, the consequences are not worth risking.

 

[Willar]

Gasgirl:

I understand you are trying to learn options and actions to take depending on various situations you may encounter during a dive. Nothing wrong with that. You will be well ahead of those people who dive computers but have no idea what it is telling them.

I have many dives around Cozumel with several dive ops along with many dives around the Carib, all with a Suunto Cobra. Some I also had a Geo 2.0 as a backup or on my son. I've not had a problem with the Suunto causing me to cut dives significantly short compared to a group. Once in a while I did keep my depth a little above the group to lengthen my NDL times, but nothing extreme. Also, I've never had a problem with any dive op pushing me back in the water when I wanted a longer SI. I think 50 minutes was the shortest I encountered, and most people agree with a minimum of 60 minutes before we actually splash back. I really think you'll have no problems.

If you do enter deco time on the Cobra, it's not a big deal. Yes, it may clear before you reach the safety stop or you may have a slightly extended stop. You purchased the Cobra to keep you safe, so follow it. If you think it's wrong, then go buy a different computer that suits you better.

 

[Mike]

Phew! Thanks for that, cbm32! I feel my SAC rate dropping.

I felt so rejected when DandyDon said he wouldn't buddy with me!!!

---------- Post Merged at 01:08 PM ---------- Previous Post was at 12:42 PM ----------



Well, I have to disagree that this thread is "utter tosh" (BTW, I had to look up the definition).

I believe I have a legitimate concern about "marginal profiles" in Cozumel based on several posts I have found on this forum. Although, there have been others who seem to think the short SI never happens, here is a reply from BradJ to a 2004 thread originally started by DandyDon describing why he ended up with a 18 min deco obigation on his Suunto:

Well it was typical Cozumel two tank diving: the first dive on a wall to around 100' for about 30 minutes, a short SI and then a fairly shallow second dive for 30-40 minutes.
The only thing that changed was the DM wanted to do Chankanab which is pretty shallow but the rest of the group wanted to do that wreck the U-???. I thought the DM was a little uncomfortable about the second dive but once in the water that wasn't the case.
That wreck is pretty deep, about 80' at the bottom. I thought we would hang out on the deck which is about 60' or so but he led everyone down near the bottom where we spent some time. About 20 minutes or so into the dive still at about 80' I realized the Vyper was almost out of NDL time. I figured the DM would plan for this and we would begin our ascent.
Much to my surprise he started to penetrate the wreck for another 5 minutes or more. I'm watching the DECO minutes start to build with the rest of the group and the DM seemingly oblivious.
Well finally we separate from the wreck and start drifting with the current, but everyone still stays near the bottom. I slowly begin ascending as the group gets smaller and smaller until I'm at 10' where the Vyper wants me and begin my 18 minute stop.
The amazing thing is a group finally does ascend but blows past me without even a SS. The DM and the rest of the group join me for their SS and a few minutes later he gives the thumbs-up. I shake my head and show him the Vyper which still has double digit DECO left. He tries to grab the others in the group but they're already at the surface.
The two of us hang out together until the Vyper clears and surface. The DM didn't want to talk about it back on the boat and the rest of the group had no clue what was going on. I did look at one guys Cobra and it was in Err mode.
I think DMs, especially in the Caribbean do the same dives every day and don't really worry about seemingly small changes in dive plans. And who knows, maybe the Vyper was way too conservative.

BradJ also posts in this thread:

"I came within a minute or two of entering DECO diving in Grand Cayman once. My dive buddy was also using a Vyper and his did enter DECO and locked him out (Err mode) when he didn't do a stop.
So two major diving destinations and two respected dive operators (Bob Soto's in Cayman) resulted in essentially unplanned decompression diving.
My question is are Suuntos too conservative or are these dives going too far.
I consider myself a fairly conservative diver. I always dive less aggressive than the DM, I'm usually more shallow than the rest of the group and I ascend very slowly."

BradJ sounds like someone I would dive with and he is only one of many members on this board who has posted this type of issue of unplanned decompression diving. Although, it would be great to say in black and white don't do it, I want to get some feedback on what to do if it happens to me on this Cozumel trip.

I have already gotten some good advice on this thread on how to pre-empt this if I can, AND how to react appropriately if it happens, AND I now better understand why it is a bad idea to rely on a computer for deco dive planning.

Thanks again to everyone for your helpful responses!

Well... his 'typical' Cozumel 2 tank dive isn't typical as has been told over and over by about a dozen people in this thread.

Around a 100ft 1st tank dive isn't typical, that's going to be atypical. About 80 feet is more typical.
A short SI (he doesn't mention time so I don't know what his short is. Maybe short to him was 3 hours?) regardless as has been beaten like a dead horse, 1 hour is typical.
A shallow 2nd dive is typical (so far that's the only thing he posted that fits in with typical
30-40 minute 2nd dive isn't typical, that's short.

So 3 out 4 of what he reported isn't typical. (he also exaggerated the depth of the c-53)

Once again, use your dive computers dive planning mode. If you're with an op who does a 30 minute SI, look at what your dive computer is telling you in regard to your next dive's bottom time, it's going to be wicked short, show it to your DM and ask him what the F is wrong with him? How am I supposed to do the 2nd dive when my computer is showing me with a 22 minute bottom time?

Maybe BradJ had been really pushing the diving, maybe the day before he did 2 morning dives, an afternoon dive and a night dive, maybe he was really pushing NDLS on all those dives, then less than 12 hours later he slams a 100 ft dive in the morning, it's cumulative right? and the dive computer will be keeping track of it all, who wouldn't be pushing deco maybe under those conditions?

There are thousands of divers a year diving Cozumel with crappy Suntos and they aren't having problems. I think you're unnecessarily over-thinking all this and all your concerns are not legitimate. and, really, if they were, it's just up to you to object to a short SI if your DM tried to push one on you anyways. Explore how to dive plan on your computer. I might be wrong but I get the feeling you might not understand what I'm talking about because if you did, I feel you wouldn't be worrying like this. On an SI I'm watching my computer and paying attention to what it's telling me in regard to my nitrogen load and how off gassed I am or not. Then a quick press of a button to look at the dive plan mode with the info the dive master gives you in regard to depth and time on the 2nd dive is a quick double check to verify I have had a long enough SI or not. In detail - if the DM says get ready to go, the 2nd dive will be a 60 ft dive for 45 minutes and I quickly check my computer in dive plan mode and it says at 60 ft I have a bottom time of 35 minutes - Houston we have a problem!

 

[DandyDon]

I felt so rejected when DandyDon said he wouldn't buddy with me!!!

:laughing: Certainly nothing personal there, just your hardware. I'm such an air hog that I am often one of the first to ascend, but I do other things to compensate - like lining up larger tanks to dive, and I hate to come up early because of a bud's overly cautious computer - which has happened to me a few times. Many divers start out with overly cautious computers that penalize divers unreasonably, as compared to the "more liberal" units that are as safe as Padi tables - no guarantees but a good record. So, when you decide to upgrade is up to you, but I just don't like diving with my bud's silly computer in control.

On the other hand, it wouldn't be hard to find info on this board that would suggest avoiding diving with me. :shocked2: You have quoted some old comments of mine that were interesting in review of old ideas, but then I am mostly a fumbling tourist diver.

I do hope your chosen Op doesn't rush you on your SIs. Being first in the water for the first dive, then last for the second dive would add some time to yours, and of course diving Nitrox on the second is a nice idea.

When are you going to be in Coz? I know of an Oceanic I might borrow.

 

[blue steal]

This has been a good thread, thanks for starting it gasgirl.
I've had my gekko for 3 years now and never a problem here in CA as most of my dives are shallow at less than 60' and multilevel up.
But in COZ I have found it (gekko) to run out of NDL (using air),well before my gas and had to level up gradualy to avoid any deco obligation.
Most dives the first has been around 80' with the DM saying not to go below 100'. I have rarely gone below 100' in COZ, well maybe at Santa Rosa wall 105' and Baracuda 117'.
Second dives around 45-60'.
Our SI's at the dive op I use are always at least 1 hour.
However on this upcoming trip I have decided to dive 32% first dive, stay above 110' (more like 80'), and do the second dive on 36%. This should increase the BT quite a bit without getting close to NDL.
Oh and I would dive with you anytime gasgirl.