Weight of the air in the tank.

[scubadada]

Guilty as charged. I'd sometimes hit the safety stop at 400 PSI. In 15' of water that lasts quite a while...

An AL100 at 400 psi has just a little less remaining gas than an AL80 at 500psi, about 12.1 cf and 12.9 cf respectively.

 

[Alan Browne]

An AL100 at 400 psi has just a little less remaining gas than an AL80 at 500psi, about 12.1 cf and 12.9 cf respectively.

Good point - I keep focusing on the PSI and not the actual gas.

More than enough for 3 minutes of SS. But I'd rather hit there with at least 500. Would also be nice to be able to help someone else if needed and not be the one most likely to need help ...

 

[Charles2]

YOU should check your zeros....

You are right, I should, thanks.

0.807 lb/cuft · 453.592 g/lb ∙ 0.0353147 cuft /l ∙ 1,000 l/kl = 12,927 g/kl

Still getting the same answer.

 

[JackD342]

The last place I dove (Roatan Fantasy Island) seemed willing to do anything reasonable to make people happy. We will be returning there this March (95%). I've asked them to convert those 100's to Nitrox. Ria replied that it should be okay, but no confirmation so far (I assume they have the expertise/qualifications to do so). I'll also ask that they be filled to 3300 if possible since I tend to go through air fast (that's the next thing I'm working on - better buoyancy and trim to reduce air consumption).

While we were there, I believe the tanks were charged the day before, so plenty of time to cool ( I didn't look into their pressure station to see if there were water baths but must assume there were...). On the boat the tanks were at least 3000 Lbs (don't recall if I saw any at 3300 ... but definitely above 3000).

They were definitely patient about people getting in full dives - no pressure from DM's to get back to the boat. I'd often be one of the first on the boat and it could be 20 minutes or more for the last divers to get back on board.

The boat captain, John, used to dive as well (fishing - a nasty and dangerous business from his telling) so extremely patient.

Sounds like your primary objective is to extend your bottom times, and you are focusing on dialing in your weights and maximizing your air fills. A couple of pounds or a few cubic feet of air more or less are not going to make a tremendous difference. You might even be creating unrealistic expectations for yourself by comparing to that diver that stays 20 minutes longer than you. Are your profiles the same up until you head up? Or are you consistently diving deeper for much of the dive? How hard are you working on the dive - swimming around like a madman, or relaxed and just drifting along? For that matter, how are your mask and fins? Do you clear your mask constantly? Are your fins efficient for diving, or better suited to snorkeling?
Lots of variables to consider, don’t over focus on the lead and the air. And some people just naturally use noticeably more or less air than the average diver. (usually related to body type)

 

[tursiops]

You are right, I should, thanks.

0.807 lb/cuft · 453.592 g/lb ∙ 0.0353147 cuft /l ∙ 1,000 l/kl = 12,927 g/kl

Still getting the same answer.

It is not 0.807 lb/cuft.

 

[Charles2]

It is not 0.807 lb/cuft.

I said that you have to watch your zeros. That does sound a little heavy, doesn't it?

I stand corrected, thanks.

0.0807 lb/cuft · 453.592 g/lb ∙ 0.0353147 cuft /l ∙ 1,000 l/kl = 1,293 g/kl

 

[Alan Browne]

Sounds like your primary objective is to extend your bottom times, and you are focusing on dialing in your weights and maximizing your air fills. A couple of pounds or a few cubic feet of air more or less are not going to make a tremendous difference. You might even be creating unrealistic expectations for yourself by comparing to that diver that stays 20 minutes longer than you. Are your profiles the same up until you head up? Or are you consistently diving deeper for much of the dive? How hard are you working on the dive - swimming around like a madman, or relaxed and just drifting along? For that matter, how are your mask and fins? Do you clear your mask constantly? Are your fins efficient for diving, or better suited to snorkeling?
Lots of variables to consider, don’t over focus on the lead and the air. And some people just naturally use noticeably more or less air than the average diver. (usually related to body type)

I'm checklisting a lot of things that consume air.

- If I have too much weight and it's below my CoG, then I'm "swimming" nose up. This causes drag, and climb and wasted energy/air correcting and so on. So: a) reduce weight and b) move the weight up.

- I've come a long way in "calming down" in the water to conserve energy/air - always room for improvement especially on ...

- I'll be working on buoyancy on my next trip there. I was impressed with the instructor down there who was teaching others on the boat ("Advanced" course) and he gave me some buoyancy tips - I may take a buoyancy course from him while there to improve. It's likely my best potential for improvement.

- Most dives my mask is "just right" and doesn't need to be cleared. Some dives it seems to leak more so I flood it and clear it. Yep - lot's of air.

- My fins are large, plain fins that I've had forever. I could look at new ones, but I'm pretty sure 95% of the problem is me, not equipment.

- Body type: I'm tall and big with a pretty huge lung capacity. That can't be overcome easily - so I have to work the other details.

20 minutes? I'll settle for 10.

Profiles? One guy I'm comparing to was all over - often 10 - 20' or more deeper than the group. One of those guys who doesn't really seem to even need air.

 

[Steve_C]

I'd assume though, that when filling, they have water circulating to pick off heat...

Not universal practice. Of the places I have seen filling I would say more do not have water circulating than those that do.

 

[tursiops]

Not universal practice. Of the places I have seen filling I would say more do not have water circulating than those that do.

Best practice today is to NOT fill in a water bath...just fill slowly. The disadvantages of a water bath are large, the advantages are small. Bad trade-off.

 

[Alan Browne]

Steve_C / turisops: The only place I recall water baths (about 2 or 3 inches of water flowing in a channel where the tanks were standing) was in Cuba as I walked by the fill line. I don't know about Roatan where I'll be going in March - but I will take a look this time.

I guess an option would be to have good air flow in the filling room.

All I see on the web (from this forum) is risk of water being blown into a tank from wet fill room equipment (esp. whips). If the cooling water is just in the bottom few inches it would seem low risk. Further, the technicians would presumably be very aware of that risk and would take care...