How to plan second dive of the day using a computer
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DuboisP
Contributor
DuboisP
Contributor
false.
you can, when you know how to, but you have to learn and practice.
but no advantage to do it, it's better to use a computer.
when you know how to.
BDSC
Contributor
This whole idea or discussion of "dive planning" got me to thinking about what I and most everyone else I have ever been diving with actually do before dives. (And here I'm talking about a typical Caribbean type of dive.)
Take a typical example of a two tank boat dive in Little Cayman. When you reach the first destination and tie up you get a briefing of the site and then the DM will say something like, "The max depth for this dive is 100 ft. and the dive time will be 50 minutes. Watch your computers and be back on board with 500 psi."
So what do I do to "plan" the dive? Nothing really. Basically we all gear up and off we go watching our computers. I quit logging dives when I reached 500 so I do have a bit of experience and pretty much understand how much air I typically use on a dive. I don't think I have ever seen anyone, myself included, actually take a computer, go to the planning stage before the dive, and run through a program that tells you how much time you will have at 100 ft. Do I really need to know before I jump in how much time I have at 100ft? If I want to know that I just look at my computer when I reach 100ft.
The second dive will be much like the first. You get to the site, get the briefing, and will be told something like, "The max depth on this dive will be 50 ft. and the dive time will be 60 minutes. Watch your computers and be back on board with 500 psi." Again, I have never seen anyone on board take out their computers to see how much time they should get at 50 ft. because in a couple of minutes when you are at 50 ft. you can just look at your computer and see.
I have no doubt that in some dive situations, maybe many dive situations, dive planning would be a must. Really deep dives involving deco, cave diving, and checking out the Andrea Doria for example. But for a lot of your typical caribbean diving, I don't see a real need for some type of formal "dive planning". Maybe the whole, "Max depth is X, dive time is Y, and be back with Z" is the plan.
Take a typical example of a two tank boat dive in Little Cayman. When you reach the first destination and tie up you get a briefing of the site and then the DM will say something like, "The max depth for this dive is 100 ft. and the dive time will be 50 minutes. Watch your computers and be back on board with 500 psi."
So what do I do to "plan" the dive? Nothing really. Basically we all gear up and off we go watching our computers. I quit logging dives when I reached 500 so I do have a bit of experience and pretty much understand how much air I typically use on a dive. I don't think I have ever seen anyone, myself included, actually take a computer, go to the planning stage before the dive, and run through a program that tells you how much time you will have at 100 ft. Do I really need to know before I jump in how much time I have at 100ft? If I want to know that I just look at my computer when I reach 100ft.
The second dive will be much like the first. You get to the site, get the briefing, and will be told something like, "The max depth on this dive will be 50 ft. and the dive time will be 60 minutes. Watch your computers and be back on board with 500 psi." Again, I have never seen anyone on board take out their computers to see how much time they should get at 50 ft. because in a couple of minutes when you are at 50 ft. you can just look at your computer and see.
I have no doubt that in some dive situations, maybe many dive situations, dive planning would be a must. Really deep dives involving deco, cave diving, and checking out the Andrea Doria for example. But for a lot of your typical caribbean diving, I don't see a real need for some type of formal "dive planning". Maybe the whole, "Max depth is X, dive time is Y, and be back with Z" is the plan.
Well in this case the DM has done the "planning" hopefully knowing the site and using experience from earlier dives there.
IMHO there is a great difference between following an instrutor or guide and really planning your own dive.
I was not able to comfortably plan my dives after taking my OW-exam. Only now after 50 dives do I trust my skills enough to plan dives in places I have been more than once.
well, I have to disagree.... for dive #1, the "60/60 - 100/25" (as well as a few more) that was part of the things we had to memorize in my training is still there (yes, Navy numbers, but will suffice) - there is also a sticker on my slate with the RNT=0 state. Also, beginning at dive #2 (or actually 1 with start time and pressure), the slate is filled in with current NDL state for the depths up to the recreational limits (or hard bottom). Start time and pressure are recorded, and its dive time (after a discussion with my buddy as to the plan of what we are doing)....dive ends, end time and end pressure recorded...
Probably because I only added a computer late in my diving as they weren't mainstream when I trained, but my wife is probably more serious about this, and she trained much after me.
I don't know, maybe I just too new.... then again, complacency kills....
Probably because I only added a computer late in my diving as they weren't mainstream when I trained, but my wife is probably more serious about this, and she trained much after me.
I don't know, maybe I just too new.... then again, complacency kills....
Another Nice Thread!
Matt, I am sure that you have the answer to your question from some of these excellent posts. ( Fortunately, I have been diving and teaching all weekend so I missed some of the inappropriate posts that were deleted. ) We had students taking Solo, Dive Computer, Nav. and OW.
The dad was taking dive computer training because I had trained him 25+ years ago using the old table. His kids, who were doing their OW's, were being trained using dive computers in their OW. ( Dive tables are explained as a historical way to dive )
We download and analyze every dive ( even pool dives ) after every dive or each day of diving.
We changed to this method in the late (90's).
We do have our students also use DiveNav.
The reason was we could see that we were spending too much time and effort on dive tables, and not preparing our student for real life diving.
Today almost all rec. divers use computers. We have required dive computers on our trips since 1990.
Do you think you would have been better off learning how to use a dive computer from day one?
Just to counterpoint here:
There is no need for a sound knowledge of decompression when purchasing a dive computer. 90% of computers out there today are designed for the casual diver in mind, not anyone requiring deco. Now as well know all computers will calculate accrued deco once you go past the NDL; however there is always the caveat in the instruction manual that you should not use this function unless trained to do so. Therefore the average computer is designed for Joe or Jacques Public, not for the versed deco diver.
As for dive planning with computers: well I'll stick my head on the block and say that I never bother. Once I know the depth of the site and general topography (i.e. I listen to the dive briefing) I will then base my dive on the NDL (plus padding) for each level of the dive; normally ending with an extended cruise in the shallows (where possible). However I know I can do this as my gas requirements are very low, and a normal hour dive will have me coming back with 100 bar (1500).
Any successive dives are followed with a minimum 1hr surface interval usually more. Again I don't use the dive planning feature, I like a little surprise when I get down to the deepest point of the dive
I should add this is not what I teach in class. This is what I do for fun dives. I'm not saying it's the right thing to do either.
There is no need for a sound knowledge of decompression when purchasing a dive computer. 90% of computers out there today are designed for the casual diver in mind, not anyone requiring deco. Now as well know all computers will calculate accrued deco once you go past the NDL; however there is always the caveat in the instruction manual that you should not use this function unless trained to do so. Therefore the average computer is designed for Joe or Jacques Public, not for the versed deco diver.
As for dive planning with computers: well I'll stick my head on the block and say that I never bother. Once I know the depth of the site and general topography (i.e. I listen to the dive briefing) I will then base my dive on the NDL (plus padding) for each level of the dive; normally ending with an extended cruise in the shallows (where possible). However I know I can do this as my gas requirements are very low, and a normal hour dive will have me coming back with 100 bar (1500).
Any successive dives are followed with a minimum 1hr surface interval usually more. Again I don't use the dive planning feature, I like a little surprise when I get down to the deepest point of the dive
I should add this is not what I teach in class. This is what I do for fun dives. I'm not saying it's the right thing to do either.
BDSC
Contributor
OP
FPDocMatt
Contributor
At first I was appalled to find that some instructors don't use the dive tables. But now I understand that the dive table is really just a second-best option, inasmuch as it has ranges. Also, the dive groups mentioned on the table are just an artificial way of representing residual nitrogen. The real thing you need to know is the residual nitrogen itself. And even that is a second-best piece of data, because you really need to know the amount of nitrogen in each of the 16 compartments.
I think starting off with a computer would not be as good as the tables if the instructor did not explain how the computer works, what it's calculating and why. Because that would be like teaching children to add using a calculator.
But if the theory were explained adequately, I think the computer would be superior, even to a beginning student.
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