Dive Planning (Long)

[mac_diver]

While there are alot of people who do not like computers, most recreational divers use computers to control their dive ( I base this statement on observation from my diving experience not any rigorous study). The comment about not riding the computer refers to people who will stay at the max depth until the NDL limit is reached then ascend 10 - 20 ft, stay there until NDL is reached, and repeat until they have to ascend due to air pressure. A safer profile using the computer to control the dive starts the transition to shallower levels well before reaching the NDL. Also include time for a slow ascent and the safety stops.

For gas planning, there are several threads that discuss calculating your SAC, determining rock bottom, and turn pressures etc. Just remember that the rock bottom calculation has to account for a slow ascent and safety stops for two divers.

Note: edited for clarity

 

[HowardE]

Kilroy...

As you will find... more of your dives will be limited by air (or gas) consumption, if you are diving with a SINGLE 80 Tank. Most recreational dives in the ocean you will probably use an 80. (I'm just generalizing, not looking for challenges)

You will find that the NDL's at nominal depths (above 80') are almost unattainable in the situation you are describing. You are swimming out, starting shallow, going deep, back to shallow, and then swimming back. Even though in your desc, you're not listing time spent... it seems to me like you'd be worried about air WAY BEFORE you hit your NDL.

There are dive tools for multi-level diving, which they teach in advanced classes. For added safety, you can plan your dive as the deepest point you go to, and stick to that as your NDL. This will ensure that you won't hit it.

Have FUN!

 

[Tom725]

Kilroy, if, as a new diver, you understand all of the above then you are far more advanced than I was at the begining of my diving career.

Planning you dive to me means deciding where you will go, what you will do on the dive in general terms - spear fish, wreck dive, look at fish, etc., - what equipment you need , and the general length and debth of the dive.

First, if you are going to a site that you have never dove before you need to talk to someone who has dove it. I recoment the local dive shop as the information is likely to be more accurate.

Decide what your goal is for the dive. In this case it seems it is to see the canyon. If you now the debth of the deepest part canyon, look at your dive tables and determine what you NDL is at that debth. Write it on your slate if you like. As a newer diver it is unlikely that you will know your exact air consumptuion so you need to watch it carefully.

If there is current or other natural conditions then you need to plan for them such as begin the dive against the current.

I do not know the site but a thumbnail plan with you buddy might be, "We descend to the mouth of the canyon and do a bouyancy check. We decend into the canyon and follow the wall. When either of us reaches 1,700 pounds we turn arround. If we are within 3 minutes of the ndl limit we determined from the table we ascend 20 feet up the wall and begin our return. If either of us are cold we go up to fifteen feet and follow our compasses in.

The dive plan should also include a review of signals and each others equipment.

I would still use a computer and you will be pleased at how much safer you feel than using the tables alone. Planning you dive per above gives you and your buddy an idea of the plan. In this case it would also remind you that you need to take a compass reading so you know where shore is if you have to look for it.

If you plan every dive minute by minute you miss that big fish or great part of the wreck because you are following a plan. The plan is a tool not the reason for the dive - unless,of course, you are an engineer, in which case plan away.

As a new diver do not push any limits. Stay shallower, farther from NDLs and come back with more air.

Remember, this is a recreation. You need to be safe but if you are not having fun there is no reason to do it.

 

[Doc Intrepid]

As a new diver do not push any limits. Stay shallower, farther from NDLs and come back with more air.

I don't disagree with Tom that when I was a new diver my dive plans were pretty simple. On the other hand, as a new diver my dives were pretty simple too. Over time as my dives increased in complexity, my plans evolved accordingly.

What I've observed, however, is that many new divers don't always stick with simple dives. They then get into situations involving things like working harder against currents than expected, thereby using up their air faster, resulting in unanticipated adventures, getting lost and/or separated from their buddies, etc. There is a fine line between a new diver doing a dive with a simple plan, and failing to discuss potential situations all the way through.

We were heading out to a wreck last March about three hours out of Morehead City, NC when the captain altered course suddenly and we saw three divers drifting, some 70 miles offshore. They were too tired to swim over to the boat, so the captain had to back the boat up to them to take them aboard. They were off a different charter boat which was still anchored to the wreck about a mile in the distance. They'd done almost everything wrong: lost sight of the anchorline during the descent, dropped to the sand anyway at ~100', had no compass heading to the wreck but began to swim in what they thought was the right direction, got lost, got swept downstream by a high current they never knew was there (because they were being swept away by it), kept on swimming anyway until one diver ran low on gas, then surfaced directly after X minutes at ~100' as the one was OOA. No SMBs inflated. They were lucky that they weren't bent in addition to being lost and adrift. The only thing they'd done right is stick together. They'd had a relatively simple plan in place: go down, look at the wreck, come back w/ 500 psi, gear check, etc. Lets just say that both their planning and their execution was inadequate for a wreck dive in nearly 100 fsw some 70 miles off the coast of NC. These three were newer divers. I heard one say to another while the third was trying to crawl up the ladder "Thats it, I'm done with this. No more for me." I was thinking "Dude, you're 70 miles offshore. Your boat doesn't know where you are and can't see you. Divers have simply vanished out here. And you didn't have any plan in place for losing the downline? Quitting is an intelligent option, unless you're willing to put a lot more time and effort into this gig..."

Bottom line is that if you're going to stick with simple rudimentary dive plans, you should be doing simple rudimentary dives.

If your dives aren't simple, better get ready to do some aqua-engineering...

FWIW. YMMV.