Reserve limit 500 psi always? What about doubles?

[markmud]

Why dive doubles on a recreational dive? I can think of at least two reasons right off hand. One is to avoid swapping out tanks or filling between dives. The other is to have lovely loads of gas for long, shallow cruises.

On our Red Sea trip, we did more than one dive that ran over 90 minutes. Why not? The water was warm, the dives were shallow and sunlit (or wonderfully dark and critter-filled) and we had SCADS of gas . . .

Hey TsandM,

Why dive doubles on a rec dive? Because you want to!!!!!!!!!!!!!!!!

I enjoyed your post.

markm

 

[The Chairman]

You make some good points; however, the OP was not tech diving.

Great point... and in reality, I dive thirds on most rec dives as well. I might not if we are doing 20 ft reef dives. That being said, I often recalculate thirds based on conditions and extending the dive. Its a big ocean... I'm not going to see it all in one trip.

 

[PfcAJ]

Hey NetDoc,

You make some good points; however, the OP was not tech diving. He was rec diving while wearing doubles equiped with an isolator. Orthodoxy can be a problem.

I have to admit that subconciously I may be siding with the OP because of my experience with dive-boat rules. The rules are made for the lowest common denominaotor. However, I am not the lowest common denominator on the boat (in the water, an argument can be made that I am the lowest cd, but courts have ruled that I am a responsible individual on all boats (not ships), whether I am a crewmember or not).

You see, I have documented, as captain, about 350,000 nautical miles on the water with the Coast Guard. I am always a little worried that a dive-boat captain may make a mistake that will put me in jail, while at the same time forcing me to follow rediculous rules.

I am always respectful to the crew of dive-boats while being fully prepared to perform my legal duty to give the captain my opinion that imminent danger is ahead. By case law, I can't sit by and watch people get hurt.

My viewpoint is probably tainted on this issue, but I will defend the OP's philosophical argument as I think all orthodoxies should be scrutinized.

markm

You and everyone else thinks their the not the lowest common denominator. Tough to know for sure, hence the checking and semi-babysitting.

If getting checked is a big deal to someone, maybe their ego needs to take a bit of a backseat.

 

[markmud]

You and everyone else thinks their the not the lowest common denominator. Tough to know for sure, hence the checking and semi-babysitting.

If getting checked is a big deal to someone, maybe their ego needs to take a bit of a backseat.

Hey PFCaj,

I wrote: "(in the water, an argument can be made that I am the lowest cd...)"

So, I agree with you on that point.

And, I understand the babysitting mentality. However, baby sitting all, irrespective of qualifications, is a lazy man's excuse for safety.

markm

 

[redacted]

Great point... and in reality, I dive thirds on most rec dives as well. I might not if we are doing 20 ft reef dives. That being said, I often recalculate thirds based on conditions and extending the dive. Its a big ocean... I'm not going to see it all in one trip.

By "recalculate thirds", do you mean you change your plan and dive in to your 1/3 reserve?

The rule of 1/3 in recreation diving is mostly a waste of gas and dive time unless you are carring a good deal more gas than you need to safely execute a planned recreational dive.

 

[PfcAJ]

Hey PFCaj,

I wrote: "(in the water, an argument can be made that I am the lowest cd...)"

So, I agree with you on that point.

And, I understand the babysitting mentality. However, baby sitting all, irrespective of qualifications, is a lazy man's excuse for safety.

markm

We had a rule that if you surfaced with less than 500psi (which isn't a horrible gas management plan for single al80 diving in 30-60ft of water, btw), you say out the next dive. There were plenty of times where I've made people side out from dives before because they surfaced with less than the prescribed minimum. It shows that they don't have the required skill and or judgement to surface with an adequate reserve, so they sit out. I call it accident prevention.

Typically, its a good time to discuss gas management with these folks. Make it a time for education. Often, they would be grateful for the help and advice. Those that weren't certainly didn't drop past the minimum again (this was at a week long diving resort place I used to work at). Either way, it ensured that the minimums were adhered to.

 

[waterpirate]

I dive alot on boats where the crew has no idea who or what about me. Follow the rules, it makes them happy. I do get ruffled at $hitty attitudes and nanny sitting, however by the second day if you got skills they shine all by themselves without any chest thumping on the dock or at the brief.

All that being said if I am diving no deco to a shallow depth the rule of thirds or any arbitrary number really does not matter to me. If I am going to do two dives on the same twinset I will call the first dive with enough gas to do the second dive safely.
Eric

Being advanced divers we should all have a grasp of what is and what is not appropriate given the conditions?

 

[The Chairman]

By "recalculate thirds", do you mean you change your plan and dive in to your 1/3 reserve?

When I dive shallow here in the Keys, I often return to the boat, or at least the boat anchor line. If I have NDL left I will recalculate and go have fun! This is especially true if the water is like glass with absolutely no wind or current to contend with. On the other hand, a kick ass current or 8 ft seas will have me go the other way and calculate my thirds from a higher baseline. IOW if I have 3500 psi on my 130 and the conditions are dicey, I will figure my reserves off of a 300 or 400 psi base. My turn would be @ 2500 psi and I'll be back at the boat with 1500 or more. Every dive is different. Obviously, if I am diving deep like on the Duane and descending and ascending on a line, recalculating thirds is a moot point. Its simply not going to happen.

 

[Centrals]

If I have to use the same twin set for two dives then I always make sure that there is at least 120-130 bars for the second dive.

 

[Mike Boswell]

I recently had to deal with an annoying charter captain.
This was an advanced o/w wreck charter.
No technical dives, no penetration, all within sport diving rules.
However a few pairs in the group were technical divers, (myself included) diving with double steel 100's, isolation manifolds reduntant regs & gauges) .
At the safety brieifing the reserve limit was set at 500 psi. In that all divers would surface with at least 500 psi min gauge pressure.
I questioned the captain about the 500 being valid for doubles, & he responded with a hard line " thats the rule" dive by it or don't dive.
I was annoyed with his attitude though, when I pointed out he was requiring the doubles divers to have twice the reserve as singles, he wouldn't listen, didn't care, no discussion.

With an isolation manifold this is not a real problem. Close the crossover. Dive like you have two singles. No biggy or dive the twins down to 500-600 psi, then close the cross over and use the remaining from one tank down to 200 or so, and still show 500 psi reserve. In fact one would finish with the equivalant of 700 psi in a single 100 cu ft tank.

I'm not one who pushes the limits & I ended my 3 rd dive of the day with 600 psi in both tanks, I didn't need to close the crossover to meet the Captain's rule.

However, I'm interested in hearing others opinions.
regards

Mike Dolson

Mike - You say this was an AOW dive with AOW rules - were they diving AL80 tanks? Were your tanks HP-100 and re-filled to 3,500 psi after each dive?

I'm assuming a few things here, like similar profiles to the outside of a wreck, and you are not an air hog, but it seems you were starting with more than double the useable gas of the single-tank divers. Assuming they dove close to their NDLs, you would have gone into deco if you had stayed down much longer. And the rest of the boat would be waiting while you finished your dive and your decompression stop. It just seems to me that if you used anywhere near your capacity, you would be holding everybody else up for a considerable length of time.

If you were doing all three dives on one fill, then I think he should have let you end with 500 psi in just one tank, like everybody else.

Edit: Oops - I just figured it out: No compresssor on boat, right?