Reserve limit 500 psi always? What about doubles?

[markmud]

By comparing observed gas consumption against expectations. For example in a 130 I have 4 cu ft/100 psi, or 20 cu ft for 500 psi. So if I'm crusing around at 15 fsw I should have about 20 minutes of gas left and sure enough that is how it works. So what does that say about all bourbon tubes being very nonlinear?

Also with 20 minutes of gas left using a goodly fraction of it seems reasonable as long as you're not holding up a boat.

Hello All,

I understand both sides of this issue--although, some of the anti-OP comments were baseless.

On party boats, we dive with some real winners. The boat's crew probably consider the lowest common denominator when setting rules.

However, most boats anchor in less than forty feet of water and usally about thirty feet. I believe a rule that demands 500 PSI below the boat and 300 PSI on the boat is more than adequate. I like kick'n'back under the boat. I see many things that I missed on what sometimes seems like an Olympic marathon swim.

I usually come aboard with 700 to 1000 PSI. Not because I am worried about approaching 500 PSI, because I am usually one of the last divers onboard and feel that I am holding-up the show.

To iterate, a hard and fast rule of 500 PSI on the boat is a joke for most 60' to 80' recreational dives. If you are deep diving, penetrating wrecks, cavern diving or performing staged decompression, the rule of thirds is something you should practice consistantly.

markm

 

[Hatul]

I'm curious why you need doubles for recreational diving, which I assume implies non deco dives? With a single tank I can easily reach deco limits on the second repetitive dive, so my thinking is with doubles, you must be doing deco dives?

 

[DevonDiver]

I wear doubles for recreational dives because it gives me more time in the rig. Time = familiarity. More opportunities to practice drills and procedures also. It helps condition the muscles for dealing with the extra bulk and weight. It improves my tech diving.

Diving doubles is the 'norm' for me. I don't need to adjust anything, or brush off the rust, when I do a tech dive... and when I do dive a single cylinder, it seems like a piece of cake.

There's also the issue of redundancy. 2 dive trip = 1 set of doubles or 2 singles. Only one of those options gives absolute redundancy.

 

[ajduplessis]

I don’t think air pressure on a recreational dive using doubles should be an issue in the first place!!!! Rather dive singles, less drag, easier and lot less weight. The only reason I see using doubles on rec is extremely high SAC and in that case I would want the diver on the boat with 500psi in any case!!

Rec dives are pressure/NDL driven, the only time pressure will run out before NDL is on very shallow dives and then it becomes a time factor. Most boats going out are running a schedule and the captain need to keep the $$$ rolling in. Around here dives are called and briefed beforehand on 50bar (500psi), NDL or 50min. Captains will extent the 50min but limit it to max 65min.

 

[DevonDiver]

Around here dives are called and briefed beforehand on 50bar (500psi),...

Actually, 50 bar equals 725psi. ...& 500psi equals 35 bar.

What these dive operations actually mean is: "back on the boat before your air goes into whatever 'red zone' you happen to have printed on your SPG". ha ha

Hard to take these 'strict policies' seriously, when they can't even been consistent between metric and imperial (or understand a basic conversion: 1 bar = 14.5psi)

So which is it? 500psi or 50bar. It can't be both...

 

[knowone]

I remember the loud ruckus amongst divers
from the bow to the stern

How many psi's have you got
How deep did you go
I went deeper than you
You've got less psi's than I got
hee hee hee p15sing up wind

I think they stopped short of comparing gauges
Does that still occur

So you just go about your business and enjoy "yourself"

Save ethical discussions for home, when you go outside
your house you have a responsibility to permit smootheness
for other peoples transitions

When during the 1700 mass the sun shines through the stained glass window and pokes me in the eyeball
interrupting the Rabbi, just doesn't cut it

When the street girls are moved from their corner, go
and find the new corner. If you complain to the council
because of your inconvenience you may find yourself
looking in another suburb or state

If there is a point to make make it on your dime
or to your wife
at least she's getting paid

no one is interested

 

[ajduplessis]

Start ascent on 50 bar, exit water on 35bar (500psi) or more. My apologies, should have been clearer in my message.

 

[DevonDiver]

Yeah, but my point was that many divers/operators I've seen do say "surface with 50bar/500psi".

How can they be strict about enforcing that, when the gas volumes are actually different between those two stated 'minimums'.

If I found an operation that did that, I'd dive my indie doubles.. it has 2 SPGs. I'd use an imperial gauge and a metric gauge. When asked, I'd show them the metric gauge... and wait for the 'lecture'. Then I'd show them the imperial gauge... and laugh at them.

 

[Colliam7]

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

I agree with the captain. I might not agree with the manner in which he may have said it (which I perceive to be part of your annoyance), but I probably would have taken the same position (and I regularly dive doubles on coastal recreational charters). It is the captain's call, his word is law on the boat, and what he set as a minimum is not unreasonable. The time to discuss / challenge it is on shore, before or after a charter trip, not during the safety briefing. (And, I don't mean that as a criticism, you probably were not aware before leaving shore that such a requirement was in place.)

In fairness to both you and the captain, as readers we don't have the context and tone of the interaction. If you asked, 'Does that apply to doubles divers?' and he gave an abrupt response such as, 'Just do what I say', I would have been put off by the response, but complied with the requirement, and not used the boat for a future charter. But, if his response was, 'Yes, I know it may mean you have more gas at the end than the single tank divers, but that's the way we prefer to do it', I would have accepted the response and moved on. Putting myself in the captain's position, if you then pressed the issue further after getting such a response, and challenged the validity of the 500 psi rule for doubles, I would have been annoyed.

As you pointed out, it wasn't really an issue. If you want to, close the isolator, keep 600 psi in your left tank, and reboard when ready. I don't usually do that on the second dive with doubles, but I have once or twice.

 

[Culcuhain]

His boat. His rules.
that about sums it up.