Kilroy:
I'm more interested to know how you determine:
Time of dive at various depths to stay within NDL. Do you use tables or dive computer simulation programs
Turn around time or pressure what are you basing calculation on
Safety stop plan
How much detail do you really include in your plan for a recreational dive what am I missing.
If I'm nuts and don't need this much detail for recreational diving...
You aren't nuts. Most recreational divers do very little planning. And, most recreational dives don't end tragically so perhaps in
most cases they really don't need to.
The problem is that when you hear about tragedies and (especially) near-misses you begin to understand that dive planning and pre-dive communications could have, in nearly all the cases, either prevented the problem in the first place or at least mitigated the consequences.
Since most recreational divers don't have the ability to foresee the future, and hence can't predict when or how a dive will suddenly turn snotty, dive planning is something that many recreational divers could improve on and be much safer for very little effort. 99% of the time it may indeed be overkill - but that 1% when it isn't can be real exciting...
Here is a basic outline that would work for recreational diving. (I'm unfamiliar with the site you chose, but its irrelevant - this outline would work anywhere.) This outline can be modified indefinitely, but its a place to start. SADDD = Site, Air (Nitrox), Duration, Depth, Direction
Site isn't only the name of the site, e.g. "Octopus Hole". It also encompasses the high/low slack tide times; any currents in terms of direction and relative strength; and weather - prevailing winds, waves (e.g. "2' to 4'"), or predicted fog - temperature changes or fronts. This information may assist in working out situational responses, e.g. "if we surface and there is a dense fog, we'll tie into a single jonline, Diver A will signal, etc." (It also gives you some important parameters in terms of deciding whether to simply call the dive and go have a few beers instead...)
Air or "gas planning" is more than simply "get back to the boat with 500 psi". One important thing to know is your personal consumption rate: how quickly you use up the air you carry. Two distinct values are your SAC or surface air consumption rate, and/or your RMV or Respiratory Minute Volume which is your SAC adjusted for depth and the volume of your tanks. SAC is pretty simple to calculate, and will give you a useful idea of how fast you'll use the air you carry. Another important thing to know is your buddy's consumption rate. The goal is to be able to identify how much gas would be needed to return
both you and your buddy to the surface from the deepest point of your dive. Then you back that amount out of the total gas available to each diver, and plan to only work with the remainder. The idea is that if you or your buddy suffer some catastrophic equipment failure at the deepest point of the dive, the other diver will always have sufficient gas to return
both divers to the surface.
One simple way to approach gas planning is to ask yourself how important it is that you return to a specific place. You can plan to use all your air, half your air outbound and the other half returning, or can plan to use thirds. If you're in a pool or confined water and it really doesn't matter where you surface as you can get out anywhere, its fine to plan to use all the gas you carry - aside from that amount you've backed out for emergency response. Under most circumstances divers often plan to use half their gas going out and the other half returning to their point of origin. In most cases this works, again, assuming you've backed out of your total gas available the amount you would need to respond to an emergency. In some specific cases it may be critically important that you return to a very specific point of origin - e.g. the anchor line, when you're diving off an anchored boat. Parameters like unforeseen ocean currents can make getting back challenging at times. Under these circumstances 'halves' may not be enough - you may even plan to use a third of your gas out, a third back, and save a third for responding to 'issues' (like trying to fight your way back to the wreck after the currents have blown you off it...) While it isn't common in recreational diving there may be specific situations where you use a tactic like this in gas planning, particularly when its critically important that you return to a specific point.
The idea is that all divers know in advance how much gas to hold in reserve, and at what point they must "turn the dive" in order to ensure - given their individual rates of consumption - that they have sufficient gas to return to whatever point has been agreed on.
Duration is your estimated bottom time, using a planned average depth and your SAC. It may also identify the point at which you agree to turn the dive. "We'll proceed along this <wall, wreck, whatever> for 20 minutes, then turn the dive and swim back for 20 minutes"...so you agree to turn the dive at EITHER a specific time, OR when the first diver hits their turn point based on gas consumption. Duration also indicates the point at which you both plan to call the dive - e.g. if your bottom time has been planned for 45 minutes, at 45 minutes into the dive - unless something has come up - the buddy team should be checking with each other and beginning their ascent.
Depth is an agreed upon depth that will not be exceeded, based on the plans for the amount of gas needed to bring both divers up from the 'deepest point'. You don't HAVE to stay at that depth, but its a "do not exceed" figure. You plan your NDL depth/time limits using tables. Your computer may give you additional time, but remember, the computer may not be able to factor in duress, anxiety, fatigue, dehydration, confusion, CO2 build-up as a result of short shallow breathing due to some issues at depth, etc. Computers are stupid. It is unwise to push them to the NDL limits. Under ideal circumstances you and your buddy may even agree in advance to extend the dive during the shallow portion at the end of the dive, but the point is to have a plan first, deviate as agreed upon in advance, rather than simply wing it from the start.
Direction includes compass bearings, direction of movement, and who leads. If you don't have compass bearings in advance, before the dive, then one diver is responsible to take bearings at the site, boat anchorage, bottom of the anchor line (on the wreck), etc. An idea of which way the current is running, and which direction was "shore" could come in handy in a number of scenarios, fog being only one... Direction of movement takes tides and currents into consideration. Move against them outbound, with them returning, generally... Leadership means who leads the buddy team. While any diver can call the dive at any time, by assigning roles and responsibilities the effectiveness and efficiency of the team can be enhanced - whether taking pictures, hunting for dinner, bringing up an artifact off a wreck, or simply exploring a reef. Leadership also includes a review of the hand signals or light signals that you and your buddy will use, especially those that indicate duress or other 'issues' that require a rapid response. Perhaps the most important part of 'leadership' and direction is ensuring that the Plan B that will be used in emergencies - who will do what, who will have what equipment available, etc. - is discussed ahead of time and agreed to by both divers.
The best way to avoid emergencies is to prevent them in the first place. Dive planning is a real easy, simple way to avoid misunderstandings, communications failures, and confusion following an encounter with high currents, poor visibility, or bad weather. Failing to plan is basically planning to fail. When you're confronted with a sudden emergency you'll tend to do exactly what you planned to do. If you effectively planned nothing, you'll do nothing effective.
Hope this helps,
Doc
