Signalling air remaining when diving with single tank divers.

[turt1e]

Appears I'm on a roll tonight with questions that probably have obvious answers. This one has been bugging me since diving sidemount for the first time with my wife two weeks ago. She was diving a single tank backmount and I of course had two tanks sidemounted on my Hollis SMS 50. First dive really wasn't an issue as far as signalling air remaining as I always had air! Second dive however, I started the dive with about 2300 psi in each tank and once I got to 1500 psi in each it dawn on me that we hadn't discussed how I would signal my remaining air. I decided to treat it as if I was diving a single tank and signaled the pressure for the higher tank. Not sure though if that was the correct approach though.

So is there an agreed upon way of dealing with this situation? I'm curious because when we hit the all-inclusive resorts that have the mandatory DM "follow me" dives you have to signal pressure once you reach 1500 psi and then the whole group ascends once the first diver hits 1000 psi. I don't want to be the cause of the whole group coming up to early on the 2nd dive since 1000psi in each of my tanks would really be 1500 single tank equivalant. Or am I doing the math wrong?

Thanks,

Paul

 

[JahJahwarrior]

Typically, with agreed upon turn pressures before the dive, we just use the thumb. Makes it simple, but also doesn't work if you have to have a DM who won't agree to it. I think it's easier than talking pressures underwater, plus unless you discussed turn pressures on the surface, knowing the current pressure doesn't mean much.

For sidemount diving, keep the tanks close and report the lower tank pressure. Agree before the dive on what each persons pressure is. Almost any dive even in doubles or twins requires dissimilar volume turn pressure matching, which is done on the surface.

 

[rjack321]

Maybe just dive a single tank like everyone does on those mandatory DM dives. Why haul 2 when you don't have to.

 

[Karl_H]

I think all you need is to pre-agree a low on air signal, typically around 70 Bar/1000 psi in total - i.e. around 35 bar/500 psi in both tanks. There's no need to give an exact figure. If you're experienced enough to use sidemount I'm sure you're experienced enough to know when your air supply is fine or low - that's just two signals?

 

[DevonDiver]

If sidemounting with recreational divers, on recreational profile dives, I'd inform gas based upon combined volume of both tanks.

Low gas would be 500psi/35bar in both tanks.

 

[japan-diver]

I would answer with total air either using volume or agreed upon pressure signals if needed. If going on DM lead dives I would probably dive a single cylinder (sidemount still but only one)- as others have said if its an easy DM lead dive the 2 tanks are a bit overkill. If you still want to dive both tanks sidemounted talk to the DM before hand to discuss low on air signs. If everyone is using the same size tanks/pressure rating you can just add your two pressures together to get the equivalent air in a single tank. (2 80's at 1000 psi are equal to one 80 at 2000psi, so 1000psi would be both tanks at 500psi).
Prearranged waypoints of turn pressure and rock bottom make things a bit easier - as you are not signaling numbers but when you hit a prearranged volume of air total in both tanks for turn and rock bottom. This signals and limits are much easier discussed on board before the dive.

 

[nwbrewer]

I signal pressure, tap the right tank and signal the remaining pressure, tap the left tank then give the pressure for that tank.

 

[DevonDiver]

FWIW, I signal pressure, tap the right tank and signal the remaining pressure, tap the left tank then give the pressure for that tank.

Don't you find that causes confusion, when faced with divers who don't understand your process of gas management?

When diving with non-sidemount/non-tech divers, I think the principle of K.I.S.S. needs to apply. KarlH hit the nail on the head. They need to know if you have sufficient air...or if you are low on air. Giving specific states for each cylinder isn't particularly illuminating, unless the recipient understands the situation that is represented. Do you have adequate air for an ascent from your current depth...and an adequate reserve to cover a delay and/or air-share to a buddy. Yes/No. Information beyond that will cause more confusion than it will provide clarity.

 

[nimoh]

I think there are a lot of advantages to diving sidemount with 2 cylinders while your wife dives a single. If you go through gas quickly and your wife doesn't (which I believe is very common), you can have some longer dives...but this is off topic.

It seems to me that it would be better to just give the pressure of one of the tanks, all she is concerned about is that you have enough gas to finish the dive and matches up with what she has left, and giving the pressure of one tank conveys that information.

 

[BabyDuck]

i'd signal each tank's contents, if there was any reason for anyone else to know them. but really, unless you're deciding about doing a jump or not as a team, why would anyone ever need to know your gas? you have enough, or you turn the dive.