500 psi on the boat?

[Blackwood]

I meant after a lobster WHILE diving or just snorkelling during the SI (looking at seals or whatever).

a'ha.

Okay, I rescind my objection

 

[diversteve]

I've never dove with sealions. Do they harass you more when you dive with snorkels?

LOL !!!! not being from B.C why do you call them sealion treats?? Do sealions eat them?

If you have a snorkel - esp. with a brightly colored tip - sealions will sometimes grab at it, and although they don't (usually) get it, the twisting typically floods your mask. I have a fold-up Sherwood Avid in my pocket for this (and other) reasons.

They also grab at fin straps, fins, bright shiny things clipped to your BC, camera lanyards etc...At least the seals/sea lions at Isla San Pedro (San Carlos, MX) do.

It's a lot of fun. I shoot video and two stopped to admire themselves in my port. Then blew bubbles and were gone...

Once at Los Coronados Isles - MX but the Pacific side off SoCal, I repeatedly felt something tugging on my fin. Thinking it was my buddy I asked him about it back at the boat but he was about 10' away the whole dive. There's a sea lion colony there also but I never saw who was doing it.

 

[james croft]

Snorkels may not be necessary for some conditions but I have been damn glad to have mine when seas kicked up and I had to do a hard swim back to a boat in a hard current. As my leg muscles got fatigued I would swith to swimming on my back to turning over and swimming face down. I surfaced behing the tag line and would have been hard to spot in heavy seas. The snorkel allowed me to make the swim. The two other people I was with did not have one and used up the remainder of their air on the surface swim. They ended up swallowing a lot of water and played out. I made it to the tag line only because I could breath better face down with the snorkel. That is why I carry one.
As far as diving and being a non-swimmer, you need to get swimming lessons and become comfortable in the water. Sort of like learning to walk before you can run.

 

[nannymouse]

It is my understanding that 500 psi is for use only if necissary. to me this means reg breathing through the surf line, boarding the boat, helping someone, swimming back down to recover your missing wife, and so on.

Keeping the tank and reg clean is also good, but I am not going to tahe the rigbapart until I am aboard or ashore.

Having a snorkle can be useful. My buddy likes to backswim while on the surface, I snorkle. He sees what's behind us, and I see what's ahead.

MMMmmmmmmm... ...bikinis!

Ocean diving without swimming skills is questionable. Surfing without swimming skills is even more so.
Relying entirely on technology to keep you alive is... shall we say, a bit sketchy. Fins get blown off, air systems fail, BCs leak, parachutes don't open. Being unable to get your own self back to the entry point is scary.

My snorkle is clear... ...a blond's favorite color! -N

 

[rigdiver]

I think boats use 500psi as a compromise. If they don't set an amount then they'll have divers coming up with 100psi or less, if they set it higher then divers will complain the boat is cutting short their dives unnecessarily.

Regulators must have about 150 psig over ambient to work. At 100 psi you can not get a breath out of the 2nd stage. Analog gauges are not really that accurate. You might have 500 or 300 psi with a gauge showing 500. 500psig is a rule founded with good rationale. I've seen brand new digital gauges hooked up to the same cylinder showing greater than 100psig difference. 500psig gives a little leeway. Some boats I've been on state "you must be able to take a full breath" when boarding.

 

[redacted]

Regulators must have about 150 psig over ambient to work. At 100 psi you can not get a breath out of the 2nd stage.

Would you care to explain that? My unbalanced 2nds get hard to breath when tank pressure falls below IP, but they still deliver. My balanced 2nds just get a little harder to breath. My scubapro D-series 2nd hardly changes until the tank is almost down to ambient.

It is not a bad idea to breath your regs down to "empty" so you know how they will perform for the last minute or so. The only reg I have that stops delivering through the primary is my scubapro Mk7. I have to go to the alternate on that to breath it empty.

 

[Rick Inman]

I can swim, but I don't like it. I've passed all the required swim tests as I moved through the courses, but I suck at it. I took some swimming lessons before Fundies a few years back, and spent some time at the Y practicing so I'd pass, and still sucked (actually, I'm a wiz at the underwater breath-hold stuff). I'm really comfortable in the water, can float around forever unaided and stuff, but in the swimming laps in the pool department, I burn out real fast.

But I really can't put a scenario together where that would matter. I'm out of gas at the surface - I've got so many ways to float until the boat arrives, or I kick to it or shore, it would take an act of God for me to lose them all. Drysuit floods, BC bladder rips, lose both my safety sausage and my lift bag and my buddy with all his stuff... I just can't see it.

Of all the rescue and emergency skills and drills, I just can't see lap swimming as one of the ones I'd ever use.

It's important to be water comfortable and competent in current, swell, surge and surf... and in good enough shape physically to handle the rough conditions when they come. But as to the lap swimming, I'm just not convinced of it's importance. I can't prove it, but I'd bet that there is no correlation between those divers who have died in the surf zone at Monastery Beach and their lap swimming skills.

As to the 500psi on the boat, it always strikes me funny that people put more emphasis on the amount of gas in your tank when it's not being used on the boat, then when it is being used underwater.

 

[Underwater Ogre]

LOL !!!! not being from B.C why do you call them sealion treats?? Do sealions eat them?

Yes they do like anything that extends away from the body...fins, snorkels...they only problem with snorkel is they are attached to masks!!

 

[on_two_wheels]

Okay, back to the original subject of 500 psi back on the boat......as a new diver, I can completely respect that guideline. However, I use a LP 95 that starts at only 2400 psi. So what should a diver return with given that scenario? My first boat dive during AOW was the deep dive. I returned with 240 psi and 2 of the other 4 students (using AL 80s) had to share air!!! Don't ask....I'm still pissed about that dive!

 

[ClayJar]

Okay, back to the original subject of 500 psi back on the boat......as a new diver, I can completely respect that guideline. However, I use a LP 95 that starts at only 2400 psi. So what should a diver return with given that scenario? My first boat dive during AOW was the deep dive. I returned with 240 psi and 2 of the other 4 students (using AL 80s) had to share air!!! Don't ask....I'm still pissed about that dive!

Well, an LP95 generally has 95 cubic feet with a 10% overfill (the labeled volume includes the hydro's "+" rating), which is 2640 psi. An AL80 has about 77.4 cubic feet at 3000 psi service pressure. 500 psi of an AL80 is right about 13 cubic feet, which is the volume remaining in your LP95 when it hits about 360 psi.

(77.4 ft³ / 3000 psi) * 500 psi = 12.9 ft³
(13 ft³ / 95 ft³) * 2640 psi = 358 psi​

Of course, trying to be too precise can be counterproductive, and many people just stick with 500 psi. That would mean that your reserve is the equivalent of an AL80 with about 700 psi remaining.

(500 psi / 2640 psi) * 95 ft³ = 18 ft³
(18 ft³ / 77.4 ft³) * 3000 psi = 698 psi​

And if you're wondering how much usable volume you'll have in your LP95 compared to an AL80 if you use 500 psi for each:

(2140 psi / 2640 psi) * 95 ft³ = 77 ft³
(2500 psi / 3000 psi) * 77.4 ft³ = 64.5 ft³​

(Which basically means that you have one AL80's worth of reserve extra, as if that wouldn't already be obvious. :biggrin

Of course, if you use "fraction of the original amount of gas" to determine reserve, keeping 1/6 in reserve on the LP95 would give you a reserve pressure of 440 psi, which happens to be the same as a popular frequency of "A" when tuning musical instruments.

95 ft³ / 6 = 15.8 ft³
2640 psi / 6 = 440 psi​