What is a dive plan on a shallow wreck?

[The Chairman]

I hear "plan your dive," but what does that mean? So help me understand dive planning with a scenario that is real...we're on a dive boat, pulled up to a wreck, it's a tug boat, the depth is 75', the top of the tug is 55', water temp is 81 at depth, viz is 15', no current.

Don't overcomplicate: It's all about setting limits and sticking to them. Every dive has 3 limits we all agree on; Depth, Time, and Gas.

Depth is usually set by the profile, your certs, and/or your skill (experience). Listen to the dive briefing to get this info.​

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Time is usually set by the boat and/or NDL. Most boats allow an hour, but the deeper you go, the less time you can stay safely. For planning, I use the rule of 120. I subtract my anticipated depth from 120 and get a rough idea of how long I can stay. 75ft? 120-75=45 minutes. Of course, your PDC will guide you far more accurately.​

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Gas is hardly ever thought through and the basic "come back with 500 psi" is the glib default on most dive boats. But when should you start up to make sure you have that much and don't have to rush? I use 100 psi for every 10 ft, with a 600 psi min. For 75 ft, I would start up with 800 psi. Of course, I have no idea how much gas you use, and it's a good idea to learn how to determine SAC and adjust it for depth. That way you can make sure you're carrying enough gas to get the max time out of your dive.​

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Once you hit any of these limits, it's time to start up. If you're at 800 psi and still have 10 minutes of time left, well too bad. It's time to go up. If I hit my time limit before all others, well it's still time to thumb the dive and start up.

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Of course, there are a host of other limits to consider which have to do with the environment. These are just the traditional 3.

 

[Rollin Bonz]

"Your plan goes out the window as soon as you get punched in the face."

(Or something like that)

Michael Reginald Tyson

One of my favorite quotes!

"Everyone Has a Plan Until They Get Punched in the Mouth"
-Mike Tyson

a variation of “no plan survives first contact with the enemy”
similar "Si vis pacem, para bellum"

Leads to "Have a plan, but be prepared for that plan to fail"

 

[wetb4igetinthewater]

One of my favorite quotes!

"Everyone Has a Plan Until They Get Punched in the Mouth"
-Mike Tyson

a variation of “no plan survives first contact with the enemy”
similar "Si vis pacem, para bellum"

Leads to "Have a plan, but be prepared for that plan to fail"


View attachment 738694

just to be clear, I made up his middle name.

 

[Rollin Bonz]

just to be clear, I made up his middle name.

lol, Pretty close... it's "Gerald"

 

[Cthippo]

Diving always throws up the unexpected. The wreck's not as they described; it's deeper (diving on high tide, the scour, it's collapsed); equipment fails; rubbish visibility; other divers causing grief (kicking up the silt, getting in the way...); a DiveMaster wanting to do a high-speed Kessel run in six parsecs and calling the dive when the gas hog runs out 10 minutes in; you see mermaids/whatever...

I don't get why visiting my mer friends should be a dive ending experience. They are really very lovely to hang out with!

 

[wetb4igetinthewater]

Then there’s over dependence on planning.

if diving teaches us anything it’s that stuff happen; things we thought we knew or expected to happen don’t happen in the way we planned.

As the Scouts motto puts it: Be Prepared.

Diving always throws up the unexpected. The wreck's not as they described; it's deeper (diving on high tide, the scour, it's collapsed); equipment fails; rubbish visibility; other divers causing grief (kicking up the silt, getting in the way...); a DiveMaster wanting to do a high-speed Kessel run in six parsecs and calling the dive when the gas hog runs out 10 minutes in; you see mermaids/whatever...

That's the fun of diving!

Absolutely. I think the only hard rule that people should follow is min gas. Now people may chime in and say millions of divers don't abide by that and they are fine. And they are correct. Properly maintained gear rarely fails, and even first stages failing closed are not instantaneous (not that I've heard of at least - I do realize that my perception is not statistically significant). Yet I still recommend abiding by that rule. I think it is acceptable to plan "let's look around, we are dropping to around X depth, we come up once we hit a cylinder pressure of Y, etc..). Simple and safe.

While the exercises in my dive planning doc are excessive (putting it mildly), that has a different purpose: give newly certified divers confidence to dive with each other and not have their hands held that is so common.

 

[DogDiver]

In response to a few others. For every hour underwater in a cave I have 3-4 hours of planning and preparation.
This process includes talking to fellow cave divers getting out of the water to describe conditions. Discuss with other cave diving teams my planned route so as not to interfere with them. If an instructor and students are in planning stage I’ll discuss with them so I can avoid their route. Discuss with other teams present any use of shared primary or jump lines. Thorough gear check and recheck. Gas analyzing of all team cylinders and cylinder identification and markings. Gas management and deco gas management and preparation. Planned dis similar cylinder volumes to set planned 1/3 turning pressure within the team. Unspool and rewind all reels and spools. Most of my dives have navigation plans for 3-5 jumps. Plus discussion with rebreather and open circuit team members on bail out procedures. Location of closest hyperbaric chamber and procedures on activation. I could go on….. but I think you get the point. As you novice divers progress through your skill levels it can get very complicated.

 

[Wibble]

Aside from being an overhead dive where there’s no immediate access to the surface, there’s little or nothing in common between wreck diving and cave diving.

The first thing about wrecks is they’re ever changing and full of entanglement opportunities and pieces easily break off. Wrecks are seldom deep penetration dives and much of the hard and fast caving rules certainly don’t apply.

Caves don’t generally change shape unless the water level rises with rain. Their basic topology may not have changed in thousands of years. Wrecks change with each passing storm and decay. In many ways wrecks are more akin to diving in mines than caves as in the environment can rapidly change — a rotting pit prop gives way.

The generic rules of caving — continuous line, rule of thirds or less — generally don’t apply to wrecks as penetration tends to be short. Wrecks demand common sense and good core skills as they normally have a lot of silt, obviously this applies to many caves too.

The challenge with wrecks is finding the fine line of exploring the marine architecture without putting yourself in danger. Most wartime wrecks are now collapsing and offer limited long penetration opportunities. Looking at the props, boilers, engines, bow, etc.

 

[Alaskan Scuba Dude]

Treat it as a shallow dive and enjoy the wreck. Compass and light is handy in case you lose your bearings.

 

[Bubblesong]

I didn’t see that you mention using a compass? My advice to any new diver is to take the Underwater Navigation course, or perhaps the Advanced Open Water with Navigation as one of the modules. Then start using your compass every dive, even when viz is great, to get used to using your compass, just as you get used to checking your air and depth regularly.