Quiz - Recreational Dive Planner™ - Max Time

[jonhall]

because in the procedures I always followed, it is forbidden to dive again before a surface interval of at least one hour!

Got me thinking so I went back about 80 two tank dives (not counting those where one was in the morning and the next in the afternoon) and only 9 had a 1 hour or longer surface interval and the shortest being 18 minutes - between 2 cenote dives.

 

[TMHeimer]

I haven't been on tons of dive charters over the years (maybe 35?). Of all these (FL panhandle, MS, SC,TX,NS), the only time it was a true multi level dive was the one I did in Texas on an oil rig. Most of the others were down to the bottom, swim around the wreck (or odd times a rocky reef) then up. It seems many divers talk of most of their dives being multi-level. Such as different decks on a wreck? Wall dives? These would seem to be less common than the ones I have done. Maybe someone can enlighten me more on this?

Re the test question: There is a difference of 5 minutes between the metric & imperial answers. I know this is because of rounding on one or the the other. Does such a difference bother anyone?--such as suppose it's the difference of going into deco or not.

 

[txgoose]

Got me thinking so I went back about 80 two tank dives (not counting those where one was in the morning and the next in the afternoon) and only 9 had a 1 hour or longer surface interval and the shortest being 18 minutes - between 2 cenote dives.

Agreeing with you, I'd have to black out a fair number of boxes in my dive tables if SI's had to be over an hour.

 

[Scraps]

TMHeimer—

I don’t think there is any standard for what constitutes a true or proper multi-level dive. Technically, all dives are multi-level (just all survived dives are decompression dives).

The brief discussion of multi-level diving in the PADI Encyclopedia of Recreational Diving acknowledges that:

—Multi-level diving was built into the wheel and the eRDPml to accommodate how recreational divers actually dive—starting deep and working their way up;

—The purpose of the tools is to reduce the penalty of the square profile; and

—Dive computers manage the task more accurately than the recreational dive planning tools.

My guess—and it is no more than a guess—is that PADI, in its quest to make the OW certification as accessible as possible had a choice between teaching the tables or teaching how to use a computer—and the variety and constant innovations involved in computers made tables the logical business choice.

It would be nice if they told students that dive tables are like training wheels and are abandoned (or kept only as a backup tool) by most divers as soon as they learn how to use a computer.

 

[tursiops]

My guess—and it is no more than a guess—is that PADI, in its quest to make the OW certification as accessible as possible had a choice between teaching the tables or teaching how to use a computer—and the variety and constant innovations involved in computers made tables the logical business choice.

Did you mean computers are the logical choice, not tables are the logical choice?

 

[txgoose]

I haven't been on tons of dive charters over the years (maybe 20-30?). Of all these (FL panhandle, MS, SC,TX,NS), the only time it was a true multi level dive was the one I did in Texas on an oil rig. Most of the others were down to the bottom, swim around the wreck (or odd times a rocky reef) then up. It seems many divers talk of most of their dives being multi-level. Such as different decks on a wreck? Wall dives? These would seem to be less common than the ones I have done. Maybe someone can enlighten me more on this?

Re the test question: There is a difference of 5 minutes between the metric & imperial answers. I know this is because of rounding on one or the the other. Does such a difference bother anyone?--such as suppose it's the difference of going into deco or not.

I would say that a large percentage of my multi level dives are as you describe, wreck dives with a sand bottom and multiple decks. Granted most of the local quarry dives are multi level but they are all within a 15-ish foot range, 25 to 40 feet.

It would be interesting if the average dive computer would also have the same rounding issues moving betwen imperial and metric. I assume not but that has zero evidence to substantiate. Otherwise, I wouldn't let it bother me. These deco limits are best but educated guesses for a wide range of conditions and a wide range of body types. If a person were worried about those five minutes, they should already be diving much more conservatively and not pushing the limits. Dive the tool you have (Navy Imperial tables, Navy metric, etc) and respect the deco limits of that tool. Adjustable DCs would be a whole other can of worms.

 

[tursiops]

The problem in the tables and losing NDL in the question in this thread is partly a rounding error, but very much a quantizing error. The Imperial question is 70 ft (which is a column on the table) for 31 mins, which is exactly a cell in the 70ft-column. The metric equivalent they use is 21m (rounded off from 21.34), but there is only a 20 and 22m column...so rounded or not you have to use the 22m column. In that column there is no 31min cell, only a 30 or a 32, so you have to use the 32 min cell, and you end up in Group P, one group worse than the Group O for the Imperial example. That increase in pressure group is somewhat due to using 22m (since no 21m was available), but mostly due to using 32 mins instead of 31 mins (since no 31m was available). If the Imperial question has said 32 mins, you would have been in Group P for both Imperial and Metric tables! After 49 mins SI, you drop to Group G from P (Metric), and to Group F from O (Imperial). It is the different PGs after the SI that drive the final 19 mins vs 24 mins NDLs (Metric vs Imperial). If 32 mins had been the BT on the first dive, such that in both systems you ended up in Group P after the dive and Group G after the SI, the NDLs would still have varied by 19 mins (Metric) and 22 min (Imperial).
Whew.

 

[Scraps]

Did you mean computers are the logical choice, not tables are the logical choice?

I meant teaching new divers to use tables instead of computers was the logical business choice for PADI.

Since there are no standards for computer displays and interfaces and since they’re always coming out with new models with new features, it would be impossible for the training materials to keep up.

That may be why PADI has a specialty course for multi-level diving but doesn’t have one for computer diving (though several courses do require computer use).

 

[boulderjohn]

When the PADI RDP was developed, there really were no computers, except maybe some early prototype models. There was no choice to be made.

 

[scubadada]

When the PADI RDP was developed, there really were no computers, except maybe some early prototype models. There was no choice to be made.

I believe the RDP was 1987-8

Hans Hass DecoBrain 1983
Orca Edge 1984
Orca Skinny Dipper 1987
Orca Delphi 1989