When to Turn Around on a Dive

[Derffie]

My wife and I recently went on our first dive trip. It was to Bonaire. I listened to the pre-dive instructions which included the approximate time for the dive. Trouble was that my wife and I certainly reached 1/3 and even 1/2 of our initial tank pressure before the turn around. We were very anxious about going back on our own. We later learned that (a) going shallow greatly increased our dive time remaining, and (b) we could always surface and spot the boat. This was greatly comforting. However, I must say that I'm still confused about whether or not I should be mostly focused on psi or dtr to determine when I should turn around. How could I have missed something so basic in my OW training???
Fred

 

[00wabbit]

You should be most concerned with PSI. It doesn't matter how much time you have left if you don't have any air to breathe.

As new divers you may go through air faster than others. You can signal the guide and give the turn around signal (point index up and swirl it around)

You are right about going shallower to conserve air. You should have learned how the density of the air you breathe increases as you go deeper. Because of this the regulator has to supply you with more volume and you go through your air faster. Staying shallower will slow this a bit.

You may also want to get an SMB so if you have to surface early you can signal the boat easier.

You can also discuss turn around or early surfacing with the guide so you can settle on a signal for 1/3 or 1/2 tank to let the guide know. But if the you can't get the guides attention and you are running low on air, surface. It's your dive.

 

[hroark2112]

Bonaire diving is great for a few things. One is improving your basic gas management skills and improving your breathing control so you get more time out of a tank. Another is shore diving navigation.

When you reach your turn pressure, you signal the DM that you're turning, get shallower, and coast back in. The rest of the group will likely catch you before you hit the boat.

 

[Searcaigh]

When you reach your turn pressure, you signal the DM that you're turning, get shallower, and coast back in. The rest of the group will likely catch you before you hit the boat.

This is great advice

+1 on having some signalling device, a simple SMB to inflate on the surface is a good call, make sure that the boat crew know that you have one an what it looks like.

 

[bradells]

My wife and I recently went on our first dive trip. It was to Bonaire. I listened to the pre-dive instructions which included the approximate time for the dive. Trouble was that my wife and I certainly reached 1/3 and even 1/2 of our initial tank pressure before the turn around. We were very anxious about going back on our own. We later learned that (a) going shallow greatly increased our dive time remaining, and (b) we could always surface and spot the boat. This was greatly comforting. However, I must say that I'm still confused about whether or not I should be mostly focused on psi or dtr to determine when I should turn around. How could I have missed something so basic in my OW training??? Fred

The main one for you at this moment, being newly certified (assuming because of your first dive trip) is gas usage.

Your going to suck back gas faster than most. We've all been there. Don't worry about being those people. It gets better as you dive more.

That being said, listen to the DM dive briefing. They will talk about the dive profile (max depth, max time), notice no minimums (unless current is a factor).

NWGreatfulDiver has some great articles on Rock Bottom and there are many others. Rock Bottom is also referred to as Minimum Gas. Learn that concept on gas usage

Having too much gas has never caused a problem underwater in rec diving. Same with coming up with too much left in your tank.

After figuring out your rock bottom, your faced with 3 scenarios.

1 All useable gas - usually for drift diving where the boat will pick you up where you are. Ie, when you hit your rock bottom, start your ascent to the surface.

2 Half usable - mainly for areas where it would be nice if you came back to where you dropped in. Ie, the boat is moored and your expected to make it back to the boat. When you hit your turn pressure (Rock Bottom + 1/2 usable gas), head back to where you entered. If you get back before your RB pressure, hang around for a bit and explore, or head up. Again start your ascent when you hit your rock bottom pressure.

3 Third usable - this is where you MUST come back to where you entered, say in shipping lanes, overhead environments, etc. similar to Half useable, but RB + 1/3usable supply.


As you get better with your air consumption, NDL/MDL will start to take affect, being that you can stay down longer without hitting turn pressures, instead, you still do your turn pressures, but include turn times based on the NDL/MDL of your planned profile as well. Whichever comes into effect first, you follow.


In short on Caribbean style charter's, let the DM know when you hit your turn pressures as dictated by the dives you are doing. Don't dive with DMs who don't listen/pay attention, are too far away 'guiding' or worse, not around.

In the briefings, they usually say maximum depth and maximum time. There is no harm going shallower and shorter.

BRad

 

[TSandM]

You know, I'd write a long explanation of how to determine your turn pressure, but Bob has already done it for me: NWGratefulDiver.com

This material did not form part of the OW class in the past. A small amount of it is now mandatory for PADI open water classes.

It was exposure to this information, and my distress at not having learned it, that turned me to GUE as a training agency. They include this in all their classes, from OW on up.

 

[oldschoolto]

It'll start getting hard breathing... Reach back and pull the J-valve rod.. This will give you the last 500psi in the tank.. Oh wait... That the old school way... never mind...

 

[Ricky B]

You know, I'd write a long explanation of how to determine your turn pressure, but Bob has already done it for me: NWGratefulDiver.com

And if you go to the last page of the article, there is a link at the bottom that allows you to download the entire article in PDF (instead of copying page by page).

 

[Bob DBF]

You should be most concerned with PSI. It doesn't matter how much time you have left if you don't have any air to breathe.

Amen to that brother!

To the OP, Check out NWGratefulDiver.comNWGratefulDiver.comhttp://http://nwgratefuldiver.com/articles/gas.htmlNWGratefulDiver.com

Of course the other articles that other Bob has written are worth reading as well.



Bob
----------------------
I may be old, but I'm not dead yet.

 

[The Chairman]

A diver's got to know their limitations and they should share those with their buddy and DM.

There are many different approaches to gas management as well as the other limitations you encounter on each and every dive. How you were taught may not, and probably isn't how your buddy or DM were taught. There is no "one way" and expecting everyone to dive just like you leads to a lot of consternation during the dive which probably results in you sucking down air even faster. It's a vicious circle but you can preempt it easily.

The solution is to communicate. You should arrive at a mutual gas management strategy, as well as limits for time and depth before you splash. Sometimes your DM will just tell you this outright. Other times you'll have to prompt them to be sure that you're on the same page. Bob's rock bottom strategy is great, but not if you're the only one using it. You'll need to be flexible. If you can't explain your strategy clearly and quickly, you just might have to settle for something a bit simpler. In addition to your gas management strategy, you should also be communicating about gear configurations, any goals, physical limitations, conditions and preferred signals. This gets streamlined if you have a consistent buddy, but it's critical with an insta-buddy. Communication becomes problematic when ears and mouth are immersed in water.

So, don't allow a failure to communicate suck the fun out of your diving. Make this a habitual part of your pre-dive routine and you'll find your overall dive a lot more relaxing.