Dive planning--how detailed...

...do you get? Just finishing up preparations for a master scuba diver written exam and got to thinking about the fact that I don't go through all the math and calculations prior to any of my dives. Mostly I note my depth when I get there and watch my SPG and note my bottom time with the general knowledge that most of my diving is not generally long enough to exceed time limits.
So how detailed do you get with your dive planning?

Depends on the dive. Depends on the overall scenario. A single dive on a single day on a single tank at moderate recreational depths in warm clear open water requires little in the way of deco planning as it's nigh impossible to get past the no-deco limits. And depending on where the dive is and who you're diving with it may not require much in the way of planning for navigation or the conduct of the dive, either... "Equipment checks complete, the usual, see you down there, let's go."
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On the other hand, if you're diving in other than optimum conditions, in an other than completely familiar place, in an overhead environment, multi-day multi-dives, deep and cold, then planning must be detailed in every respect, with much written down in advance and carried along, as well as safety drills conducted before descending. In that case you may do hours, days or even weeks of pre-planning for a dive.
It just depends.
Rick

Rick nailed it perfectly.

WWW™

Rick summed it up. On basic recreational dives, we might just say we'll come up with 400psi, and that's it for the plan. Most of the time, however, we're doing deeper stuff with pretty thick deco ceilings, gas switches, wreck penetration, and sometimes a second dive. We might spend an hour of discussing the dive(s) throughout the week preceeding the day of diving.
All kinds of thing would be discussed -- max depth, back gas, deco gas or gasses, bottom time, deco times, minimum tank pressure allowed, back up tables, back up deco plans, emergency ascents, and then the dive objective itself. A story comes to mind when we were diving the Mahi wreck in Hawaii, and the recreational dive master asked us what was our dive plan for this recreational 90' dive (single 80's). We looked at each other and told her jokingly we'd be up when we ran out of air. They didn't like that much , but we knew that such a basic dive wasn't much to worry about.
Rick was right, it just depends.

Mike

This topic came up just in time. We are having a SCUBA Club camp out this weekend and we are renting a compressior as the nearest dive shop is about 1 hour away and we plan on doing about 3 - 4 dives a day. I have a computer, but I would like to keep a manual journal and backup plan. Anyways if I am not sure of the first dives depth how can I plan 100%? Do I just say I am going to go no deeper then X feet .. but what if I am at X feet and I am still not on the bottom? Now keep in mind these are just recuration dives and will not exceed 100feet none of that TECHie stuff you guys are in to(YET!). I know it will depend on my SIT and other factors but these are the kind of questions I have.

Brad

NINman,
In my case I dive in pretty much the same locations and know a fair amount the location and about the depths I will find the bottom. Sometimes I don't want to see the bottom and I will simply pick a depth arbitrarily. In the situation you present I would try to find out what depths you can expect prior to this weekend. Lets say for the sake of discussion you find that the location is 70' at its deepest and at its shallowest you have a depth of 25'. If you can determine where those depths are located and some other depth locations then you can plan your repetitive dives accordingly.

For other divers does any one plan diving with air consumption rates etc in mind?

JBD, if we're diving deeper than usual or longer than usual, we look at our air consumtion and bring out the calculators. Knowing your consumption rate is extremely important in order to calculate bottom times and deco times, and therefore the amount of gas needed for the dive. For simple recreational dives or very basic deco dives, we don't pay much attention to anything except air presure and our location underwater.
Up here, other factors often play into the equation for us such as getting cold. It's not often important to me to stay on a wreck for 90 minutes at 180' since I live a relatively short distance from where I dive. Besides that, it's pretty friggin' cold down there. Also, I don't like hanging forever so we often let our comfortable decompression time tell us how long a bottom time we'll have. More often than not, we just use the exact same plans that we have used in the past and you just get familiar with them. Again it all depends on the dive objective.

NINman, I think I understand your dilemma. You have a computer, but you don't want to rely on it, right? OK, if you're staying recreational, it's pretty simple. Take a water proof watch and a slate with you with a list of depths and their NDLs. Go to any depth you feel comfortable with and use the slate for back up. This will would work for the first dive, but repetitive dives get tricky if you 'puter chokes.
To really get out of the whole mess, you should learn the guts of decompression diving, and you can bail yourself out if your computer dies. For the type of diving you are talking about, there's nothing to be really worried about if you computer dies underwater -- just ascend slowly(30FPM), do a 5min safety stop, and always go slow from the safety stop to the surface. If the computer dies sometime during your trip, then you have no choice but to use tables (unless you're comfortable sharing a buddies 'puter). We use computer generated tables for our stuff.

Mike