2700 psi vs 3000

[Rudyh]

Fellow divers quick question. Going on a cruise at the end of this month and plan on doing about 10 dives. Question is on cruise ship dives everything is planned out pretty much ahead. The dive boats are usally in cahoots with the ship. Some dive boats say 2700 psi is fine and others insist on 3000. Should i refuse a tank with 2700 ,2750 psi or just go with the flow because the dive is so controlled. Is 250 to 300 psi that much of a big deal. Thanks everyone , Rudy

 

[TMHeimer]

Depth would seem to be thing to consider.

 

[Blackwood]

All else being equal, less gas = less bottom time. How much are you paying to dive? Only you can determine whether it's worth it to you.

 

[Garrobo]

If EVERYBODY has 2700 in their tanks it is to shorten the dive. Probably a time limit to get the dive done and back to the ship on time. 2700 on a shallow reef isn't too bad.

 

[jbtut]

If EVERYBODY has 2700 in their tanks it is to shorten the dive. Probably a time limit to get the dive done and back to the ship on time. 2700 on a shallow reef isn't too bad.

I think this is correct. It's not uncommon to get 33-3500psi. I'd consider anything below 2900 "low" If the tanks are all a bit low, it's probably to shorten the dive. Another trick to shorten a dive is for the DM to swim fast to make you exert yourself more and burn through more air, or to dive into a current which will do the same. It also depends on how much air you use. My wife prefers a 60cf tank and has very similar ending pressure to me with an 80. For longer boat dives I'll breath off her octo on the way down and swap back to mine after that. It's not much but will extend the dive a minute or two. And she'll always come up with more left than me.

As for the cruise ship diving, I've always wondered about what type of cut the Cruise ship gets. Some places really aren't that bad price wise. And some locations like Belize, because of how far out you have to tender, the cruise ship dive contracts are really the only good option. Other places are easy to arrange off the ship and you can avoid the large cattle boats.

Good luck.

 

[redacted]

If you think you need more gas, then ask for a tank with 3000 + if they have it. Wife and I are both pretty good on gas so I don't usually mind one that is a little light like 2700. I doubt if such light fills are often done on purpose. But with central fill facilities and small leaks, such occasional light fills are not uncommon. Not really under the control of the boat crew or DM. If you find that you are the boat air hog, then ask for a tank with a good fill so you don't unnecessarily limit other divers' bottom time. You can also stay a little shallow when possible to extend your bottom time. Even 10 ft can make quite a difference.

 

[hudson]

TMHeimer is right, it's all depth related...let's say your rock-bottom is 1400 psi (to pluck a number out of thin air). This means your bottom gas is 1600 psi with 3000 psi initial, but only 1300psi with 2700psi initial. You can extend your bottom time 23% with the 3000psi fill. So the difference is not 10% but 23%.

OTOH on a shallow dive when rock bottom is 600-700 psi, it doesn't matter as much. So insist on full(er) fills when diving deep, maybe 70ft+

(Keep in mind if the tanks are sitting under the sun, they'll also cool down significantly when you hit the water)

 

[ringmod65]

Multiple days of diving with two different Caribbean charters recently and there wasn't a single cylinder on any boat filled past 2700.
Inconvenient if for no other reason than I know my burn rate on a 3000 psi 80 pretty well. I wound up checking my SPG a whole lot more with the lighter fills.

 

[TSandM]

Well, 300 psi in an Al80 is about 7.5 cubic feet of gas. If your SAC rate is about .7 (not uncommon for an adult man) that's ten minutes of gas at the surface, or five minutes at 33 feet. I'm not sure it's worth complaining about, especially as most guided dives don't allow enough time to exhaust the usable gas in the tank, anyway.

 

[CamG]

Greetings Rudyh and welcome to Scuba Board. Congratulations on your upcoming trip and ten dives is a big enough $$$$ to demand 3000 psi in a AL 80. When we splashed in Mexico our tanks were never under 3000psi. Sometimes they were over but not for long. The point of starting the dive with enough gas to safely do it is a major factor. Some dive op's want a 500psi reserve minimum after the dive is over. This is a very conservative limit actually it would be better to have more psi for reserve just in case.
I know that many will argue this but it is my practice and has served me well.
I do not jump up and down and make a huge scene when tanks are not filled to 3000psi just rather ask them to be topped off before we leave. IF there is a issue with it I ask for a refund and go else where. Let them know this when you are selecting dive operations to use on vacation. I think you will find many are willing to work with you.
When comparing dive op's with one another to get the best deal be upfront with them and demand the same from them. A quick search here on Scuba Board will speed this process and make it easier for you to determine what op to use.
CamG Keep diving....keep training....keep learning!