Dive Comp for OW+AOW

[Ann Marie]

I have a question for Ann Marie since she is an instructor. Please forgive my ignorance as I have not taken AOW.

Scenario:

You and I agree to go on a dive. The dive is on a wreck with the bottom at 80ft. There is moderate current necessitating us using the line to descend and ascend. We are both using AL80s. Assume the wreck has 20ft of profile so we will be between 80 and 60ft during the dive.

During our pre-dive briefing, what would you suggest we use as a turn pressure for the dive? Please bear in mind, that even if something goes wrong, I am not interested in trying a CESA from 80ft, and I would set a requirement of being able to have both of us complete our three minute safety stop.

So again, at what pressure would you suggest we end the dive and begin our ascent?

Thank you.

I say we pretend that you are taking a AOW class and you have choosen to do the wreck adventure dive. One of the first things I would do is to take you into the pool to assess your skills. I also would take a look at your dive log with you to see what kind of diving you've been doing...are you a new diver or have you been diving a while?

From there we would take some time to discuss SAC rates and you would learn how to calculate yours and use that information when planning a dive. We could then plan our dive. The wreck dive wouldn't be our first open water dive either. Our first dives would be a navigation dive and perhaps one of the other electives. That way I also have the time to assess your OW skills. We would then do a deep dive together (close to but not exceeding a 100 feet). Then we could go on to the wreck adventure dive.

We would have already done a deep dive (close but not exceeding 100 feet) so that you would be prepared to go past 60 feet. I would have our turn around point be at about 2000 psi giving us plenty of time to complete a deep stop as well as a safety stop (safety measures that I always follow). Since I'm in California and most likely we would be diving the Yukon off the Lois Ann where we always use the line to descend and ascend. The water is temperate out here, we can run into currents, and viz can be awful (close to your senerio). I would also take this opportunity to have a hang bottle and a jon-line. May not be needed but why not give the student exposure to some of the equipment that they might use in the future if they get into wreck diving? (BTW, if it is an adventure dive, we would not be doing any penetration.This boat also has 100s available, so reality we would be using those.)

I've have presented this senerio as if you were taking an AOW class and using 80s so that we could keep within the scope of this post, hope that is acceptable.

 

[Ann Marie]

Not diving a computer which is routinely sold to EXTEND the NDL beyond the tables.

I'm not sure what you mean by this statement. (Truly, not being sarcastic.)

Computers just give you credit for the time spent at an actual depth, whereas with a table you have to plan for the maximum depth no matter if you spend one minute or twenty minutes there. Computers like tables are just a tool, people need to use their brains as well.

 

[lamont]

Hello,

This is a question for the veterans. I'm taking an open water and advanced water course in succession, is it recommended to buy my own dive computer prior to taking both courses?

I'd suggest a Suunto Vyper wrist-mount computer. It'll do EAN up to 40% and is nice and conservative and has a good gauge mode if you go the gauge-mode route for trimix later (and if you go he trimix-computer route later you'll be buying a VR3 or something like that which is ludicrous overkill at this stage).

In general, I would make sure it did Nitrox, but I would avoid air-integration and I would go wrist-mount rather than console mount. The computer will be your depth gauge and having it on your wrist is more convienent for referencing depth frequently than having it on a console. Don't spend more than about $350 on a computer. The more expensive models have air integration and multiple gases and trimix and other thing which you won't need for at least 2 years and you may not ever be interested in.

 

[PerroneFord]

I've have presented this senerio as if you were taking an AOW class and using 80s so that we could keep within the scope of this post, hope that is acceptable.

If this was an accurate account of how you do AOW, you are a credit to your profession. I have seen and read accounts of numerous AOW courses and the read NOTHING like this. Well done.

 

[Ann Marie]

If this was an accurate account of how you do AOW, you are a credit to your profession. I have seen and read accounts of numerous AOW courses and the read NOTHING like this. Well done.

Thanks. I try and hold myself to a high standard and am always evolving to give my best to students.

I have learned much from some of the instructors on this board! I used to offer to teach SAC rate calculations to divers in AOW that were interested. Now I don't offer, we just do it.

 

[PerroneFord]

In reading my statement I can see where it would seem misleading. My intent was to convey that computers are often sold as a way of extending bottom time for divers beyond what the table would give. As you note, they do this by giving credit (sometimes) for time spent shallow. Where this falls down is if we are doing that 80ft dive, and I get to within 5 minutes of my NDL, I am somewhat over the comfort limit for trying to get myself and a buddy to the surface. If I then rise to 60ft, my computer will say I've got another 20 minutes of NDL, but my gas supply doesn't get an larger.

You are correct. Computers are a tool. However, they are generally of limited use, though most divers won't see it that way. Inside NDL, well planned dives are nearly ALWAYS gas limited. And outside NDLs you are only concerned about the gas limits anyway and the computer becomes mostly unimportant.

Your comment that people need to use their brains is truly the crux of the matter. Which is why I'd like to see new divers forgo the computer for trhe first 30-50 dives. Develop proficiency with the tables so that you have some idea what the computer is actually telling you. I vividly remember "bending" my computer on the last day of cave class. After exiting little river, and finishing deco, we were debiefing on the surface. I dropped my fin in the 4ft of water we were standing in. I bent down to get it with my right arm, my computer recognized it as a "new dive", and signaled that I was now "bent". I laughed and walked out of the water. Had that happened on a liveaboard or a dive vacation where the guests are "required" to use computers, I would have lost 24 hours of diving.

Guage mode is a beautiful thing.

I'm not sure what you mean by this statement. (Truly, not being sarcastic.)

Computers just give you credit for the time spent at an actual depth, whereas with a table you have to plan for the maximum depth no matter if you spend one minute or twenty minutes there. Computers like tables are just a tool, people need to use their brains as well.

 

[Ann Marie]

I should certainly hope instructors know about computers and are perfectly capable of guiding a student.

I don't make comissions on dive gear and even if I did I would guide a student to equipment that is good for them not for the dive industry.

The fact of the matter is that a huge number of divers never stay with the sport long enough to derive any benefit from the computer. Having a computer will not make them any better as divers. In fact it will short circuit all of the basic theory they were (hopefully) taught.

A couple of things, people that own gear dive more. They've made the investment and are going to dive. It is easier to load gear from your garage than to drive somewhere to rent it.

The OP asked if it's advisable to buy a computer to go along with his OW & AOW classes. I say wait to see if you like diving before you move to the next echelon of investment.

Agree for the most part. I was one of those people that wanted to dive for as long as I could remember. I knew that I would love it and if I had had more guidance from my instructor, I would have bought all my gear. In fact, I did buy a used BC off ebay that I upgraded quickly.

Ebay and bankruptcy courts are littered with the shattered dreams of divers that over invested or prove to be under inspired.

LOL! Do you really think that purchasing SCUBA gear really sends those people to bacnkruptcy courts? I think that there are some bigger underlying problems.

A diver can make the investment when his or her diving and abilities dictate, not just because they are doing OW or fast tracking into AOW (another debate). It's not like insurance enrollment where you have to sign up now or wait.

Again, we agree. I would never push anyone towards buying gear until they are ready and only require a few personal items for classes. Everything else can be rented.

I see many divers who dive sans a computer and by the same token many computers that go on dives where they are of no real value except to maintain statistics. Not every diver's dives or diver's locales are the same. Not every diver does exclusively boat diving and goes to 100 feet with lots of air and a great SAC.

Perhaps it is locale but I can not think of the last time I saw someone dive without a dive computer. Even shops out here rent computers on reg setups.

That's really good but not every new diver has a guardian angle like you. Many run out ill advised and buy according to the wrong criteria. Please take this as a compliment wen I say that the situation you present is above average in the industry as I have experienced it.

Thanks, I try. When I started diving I was not encouraged to continue with any other classes. If I was not the type of person that I am, I probably would have dropped out of diving. I didn't have much guidance on gear and ended up buying alot of gear that I have had to replace. I encourage students to continue with their diving education as well as encourage them to purchase gear, when they are ready and when they can afford it. I see my students as my future dive buddies. I tell them where I feel they need to buy the best they can afford and areas where they can cut back a little. I try and offer the features and benefits of a piece of equipment and then the rest is up to them.

One last comment (I know long post), but if the theory of decompression is taught well and is understood by the student then one does not need to use a table to get the gist of it. They do need to understand why there are NDLs, safety stops, and ascent rates.

 

[mjatkins]

I am a fairly heavy breather, as I am a very large guy. My dive planner shows the following for a 25 minute dive to 80ft.

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 2

Dec to 80ft (1)
Level 80ft 23:24 (25)
Asc to 20ft (27)
Stop at 20ft 2:00 (29)
Surface (29)

68.2 cu ft TOTAL

Basically, it says that I would need 68 cuft of air to complete this dive with my safety stop. At minute 25, if my low pressure hose ruptured, and I had to shut off my tank, I would have burned about 60 cuft of air or roughly 3/4 of my tank. Converted to PSI, that would be 2250 gone and 750 left. If we assume my buddy breathes similarly, we now must share 750 psi to get to the surface. That gives us 375psi to find the line (while sharing an octopus), get to 20ft (or 15ft), finish a safety stop, and get to the boat.

I see your dilemma. Based on this scenario with the numbers you have given, this would be a concern. However I am not convinced that your consumption rate is typical and it would seem from your statement that you may feel that way as well. I commend you on your ability to have a realistic look at you own limitations as a diver and adjust your behavior accordingly. Out of curiosity, what conclusions have you drawn from this, regarding the point when you personally need to turn the dive?

Matthew

 

[spectrum]

Ann Marie,

The OP wanted to know if buying a computer before OW & AOW courses was recommended. We are obviously dealing with an rookie. I stand by my statement that if someone was pressing him to invest in a computer he should run the other way. A computer is not needed for for those dives and it should be added when he has established his needs and understands what he is buying.

As for the rest, we obviously dive in two different locales and that's the way it is. I am sorry if you took my point blank advice as some sort of attack on you or your fellow dive professionals but there are a lot of divers out there who have bought the wrong thing at the wrong time for the wrong reason. I can see that we agree on far more than we disagree about including some of your points that you did not phrase as being in agreement such as the desirability of owning ones gear ASAP.

I can live with that,
Pete

 

[SparticleBrane]

I recently taught a EAN class, I had the students bring in their computers so we could go over setting them to EAN Mode. One of the students found out THAT night that his computer wasn't EAN compatable. If I had been there helping him to pick one out, he would have known it was or wasn't compatable.

Question--why are you showing these students how to get their computers into nitrox mode?

It would seem to me that doing it for them only increases their dependence on you as an instructor and authority figure, instead of getting them to think for themselves. Personally, if someone had come to me asking how to get their computer into nitrox mode, I'd ask if they had read the manual for it yet. Chances are, they probably didn't. If they had, I'd get them to do everything they possibly could to find the answer for themselves (give them hints of where to look in the manual, if they don't have the manual I'd suggest they download it online, etc) instead of spoon-feeding them the answer.

The same goes for the story of the student who didn't realize his computer wasn't nitrox compatible--did he not read the product description when he bought it?! If he's that inattentive when shelling out money, how attentive will he be on the dive? Same as above--coddling students doesn't do them any good; it only increases their dependence instead of turning them into thinking divers. This guy learned the hard way, but he probably won't make that same mistake again.

Not jumping on your case...just something to think about.