Boat diving - Tank valve on or off during trip?

OK, don't shoot me down in flames if different organisations have strict views on this but I have had different opinions.

When diving from a medium size rib one instructor I have dived with always get the bcd and tanks loaded onto the boat with the air valve open - she says if an o ring is going to blow then it usually happens fairly soon after pressurising and this is the best way to be sure it won't happen during the dive. However other people I have dived with only turn the valve on just prior to getting in the water, saying, with some justification because I have seen it happen, that a regulator or octopus can get knocked or held open slightly and lose air on the trip out.

My experience is as limited as yours. I believe that will be up to the dive op.

The operators I've dove with kept the tanks closed until a few minutes before splashing. My buddy can't open his until just before splashing because of the synching procedure for his dive computer.

I dive regularly and always setup gear and test it at the dock before getting underway; Open the tank full, ck reg's, octo's, gauges, bc etc.. Then turn everything off and deflate/relieve pressure...Until just a few minutes before getting in the water....I've never had a problem or unpleasant surprise w/that routine.......But, because I dive almost weekly and have different setups for different enviroments I change out parts, "O" rings especially and do routine maintenance almost monthly...I've learned from experience this prevents surprises...Sadly it's the 2-3 times a year diver who thinks because they don't use gear often it rarely need maintenance and can sit in a garage/closet indefinitely w/o up-keep...The opposite is true...That gear needs to be gone thru each time it's pulled out from storage before a dive....I see that situation almost every time I dive....Most of the time it's just an "O" ring, but I've seen worse.......Take care of your gear, ck it regularly, follow the manufacture's maintenance schedule, ck it at the dock and you should be trouble free......

Good question. Here is my opinion: I don't care which method you use, both are acceptable to me. HOWEVER, if you choose to turn off your air for the ride out bleed the hoses or take 5 or 6 breaths before entering the water, while looking at your pressure gauge.

It saves a bit of crisis management by doing this.

Assemble equipment, test, shut off air then back on again when getting ready to enter the water. for me it is because I am trying to save battery life in my transmitter. No need to have it pressurized and draining my battery until I am ready to dive.

IMO I would keep the valve off until it's time to get wet. Buddy checks are supposed to be back up to ensure tanks/air is on. You are ultimately responsible to ensure you have opened your tank valve.

Once when I was diving I got back on board after the first dive then changed out tanks to new tank. I set up my BC on the new tank and checked my guages and had about 3200 PSI in the tank. I thought, "cool, maybe can stay down little longer extra PSI." After the 45 minute surface interval checked my guage before getting in and to my suprise the tank had leaked down to 2800 PSI. O-rings were intact as well.

Just to prevent inadvertant air leakage I'd say keep the valve closed until time to get in the water. YMMV.

I NEVER leave my gear with the tank valve open and the regs pressurized for anything exceeding a few minutes. Doing so in some places (yes, places not cases) does NOT reduce the chance of o-rings blowing, but pretty much guarantee it. When I dive in tropical locations its pretty much 1 SI, 1 blown o-ring and that o-ring is on whoevers tank that forgot to turn the tank valve off and depressurize the system..

Any time I have the gear on my back, the valve is open. If it is riding in the floor of the RIB, the valve is closed. It's all too easy for a purge plate to get pushed on by some other piece of kit, and for you to arrive at the dive site with half a tank of gas. With the engine running and the wind blowing, you might not hear it at all.

Tigerman:

When I dive in tropical locations its pretty much 1 SI, 1 blown o-ring and that o-ring is on whoevers tank that forgot to turn the tank valve off and depressurize the system..

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Really?! I doubt I've seen ten O-rings blown in several hundred surface intervals in the tropics.

I check my gear once I assemble but shut the gas off and purge until I am ready to gear up! I turn my gas on, gear up, test both second stage and octo while watching the PSI, stand in the door...!!!