Air on or off on boat ride to dive site?

[Noboundaries]

Maybe this is a REAL basic question, but I'm going to ask it anyway. Once you set your gear up on the boat and do your pre-dive checks, do you leave your air on or turn it off on the ride to the dive site? Same question for the surface interval between dives. I'm asking because I've seen people do both on dive boats.

Personally, my wife and I leave our air ON for the following reasons:
1. Unless you purge your regulator once you've checked tank pressure, the residual pressure in the hose will still register on your computer or gauge, giving a false indication that your air is still on. The residual pressure will usually equal tank pressure.
2. Leaving the air on will indicate whether you have a leak or not. Usually you can hear leaks at the first stage or a hose connection, but not always. A dropping pressure will indicate a problem.
3. If an o-ring is going to fail or a hose connection come loose, it is better to happen on the surface on a thirty minute to two hour ride than submerged. My wife and I have had both happen (o-ring failure and hose connection come loose).
4. If we don't have our inhalation effort knob positioned for diving and our venturi switch positioned properly for a surface interval, our regulator will free-flow easily with the slightest bump. When set properly, surface free-flow isn't a problem.
5. Leaving the air ON is our habit pattern. I learned in another profession that broken habit patterns are the #1 cause of user-fault accidents. Once we do our pre-dive checks, we keep a very watchful eye out for a crew member messing with our air. If we leave our gear unattended to go to the head or visit another part of the boat, we always check that the air is ON when we go back to our gear.

I know crew members always check air before you splash, but frankly I trust myself more than them.

 

[spectrum]

I'll be the first to say that boat diving is not my forte.

5. Leaving the air ON is our habit pattern. I learned in another profession that broken habit patterns are the #1 cause of user-fault accidents.

What I will say that your number 5 is the prime directive in my book.

Pete

 

[Underwater Ogre]

Doesnt really matter as long as it is on when you hit the water.

 

[SteveAD]

I follow the same procedure for the same reason.

 

[AndyM]

I'm glad you asked this question. I had the same one.

After many lake dives from shore I did my first boat dives this weekend and wasn't sure what to do. I own a Sherwood reg that has an air bleed on the first stage. It allows a small amount of air to bleed through when the air is on. I was worried that I would loose air (albeit a VERY small amount) and shorten my dive later. I turned the air off, but maybe someone else with a Sherwood first stage can alleviate my fears.

 

[Damselfish]

I think habit is more important in this case than what you do. That and always checking.

Our habit is to turn on and check things out, turn off and purge, turn back on when getting ready to dive. One thing about leaving it on, we're often on a liveaboard so if we left it on it when we first turn it on it might be on for a long time if we skipped a dive, or overnight. Usually your tank is refilled before you leave the dive deck from the previous dive and we put the reg back on and check it then.

 

[hudson]

I turn if off and depressurize. Leaving the air on puts pressure on the first stage. For a short ride, it's a non-issue though.

 

[Peter_C]

Mostly I follow the procedure like the OP. Once in awhile under certain circumstances, I will turn the air off and immediately bleed off the residual pressure. Stupid mistakes are preventable by procedures.

The other one not mentioned is air "completely on" or "completely off", but never just crack the valve.

 

[spectrum]

I own a Sherwood reg that has an air bleed on the first stage. It allows a small amount of air to bleed through when the air is on. I was worried that I would loose air (albeit a VERY small amount) and shorten my dive later. I turned the air off, but maybe someone else with a Sherwood first stage can alleviate my fears.

Don't let the dry bleed consumption modify your procedure. The loss really is slight.

 

[don Francisco]

Doesn't really matter and might vary according to the length of the trip. You raise valid points for leaving it on, the most important of which are the first and last.

If you turn air off after turning it on, always (as a matter of habit and without needing to think) bleed the air out of the lines to prevent a 3000psi gauge reading from letting you think the air is on.

Always verify that the air is on by checking the tank valve, even/especially if you left it on, at the last moment before sitting down and strapping on the BC/tank. This is beats watching your setup or worrying whether someone might have turned the air off since it guarrantees air is on either way.

The last point is the most important, and reinforces something I was taught when setting up machinery. -- always do the same task the same way, every time. Solid habits, so ingrained that you do them without needing to think, will protect you if and when you get distracted.