Tank configuration

[tbone1004]

Um, no. You don't base your usable gas for a dive on the amount of gas you started your last dive with.

I agree with most of your last post but absolutely not this.

I was thinking the same thing as I read @halocline first post, but I can see where the logic came from, and I agree that the original point of 1/6ths wasn't to give additional gas to "solve problems", but to "limit penetration".

Rule is 1/6th of doubles, or 1/3's of singles. If using al80's filled to working pressure, that is 1000psi "total", being 1000psi out of the one tank, or 500psi out of each tank.
His instructor probably interpreted that as you are allowed 500psi of penetration, and provided that the 500psi does not exceed the third of the full capacity of one tank, then you are fine. i.e. can't do a 500psi penetraion if your tanks are at 1200psi, but you can do it if you start at 1500psi.

Now, will the agencies agree with that? Probably not, but I don't disagree with it, and I think it is much more inline with the spirit of the original rule than what is being interpreted.

 

[halocline]

I
Rule is 1/6th of doubles, or 1/3's of singles. If using al80's filled to working pressure, that is 1000psi "total", being 1000psi out of the one tank, or 500psi out of each tank.
His instructor probably interpreted that as you are allowed 500psi of penetration, and provided that the 500psi does not exceed the third of the full capacity of one tank, then you are fine. i.e. can't do a 500psi penetraion if your tanks are at 1200psi, but you can do it if you start at 1500psi.

This is pretty much right, and I doubt that the agencies would have a problem with it. Otherwise the "1/6 doubles-1/3 single" rule would make no sense. The 1/6 penetration limit for doubles is really not a gas planning issue, because according to the rule an intro diver can do the exact same dive (26cft used on penetration) on a single tank, i.e. with half the gas. In fact, a 500 PSI penetration with doubles filled to 1500 is exactly the same plan as a 1000 PSI penetration with a single tank filled to 3000, which is allowed by the agencies.

One thing, though, the way I was taught you can't do a 500 PSI penetration with 1500 in doubles, you can only do 250PSI. You have to leave the original 1000PSI as a reserve on any dive. So if you have 1500, it's 250 in, 250 out, 1000 reserve. The only way you can do a 2nd dive with a 500 PSI penetration on a set of doubles is if you started with 2000 or more.

 

[Subcooled]

I want to go longer, and to the maximum depth and penetration.

You know it's a one-way ticket?

I also want to limit the time spent fumbling with gear on land. I also want some redundancy.

A contradiction.

A backmounted doubles set might be a little bit easier - especially onboard RIBs.

So, which is better - doubles or sidemount?

Sidemount is flat but wide (but you can do no-mount diving through flat and narrow sections when needed). Really nice in tight caves. Backmount is tall but narrow. Maybe better inside wrecks. Don't know. Prefer them floating. Sidemount makes your back flexible (and the valves accessible) while backmounted doubles comprise a single integral set. Underwater acrobatics or on-the-surface-ease? Now choose...

 

[shoredivr]

I am of the attitude that I should be diving similar equipment as those I am diving with. For instance, we all are diving dry, or we all have the same tank configuration. While there, I noticed others diving with SM. So, my logic tells me that maybe I should dive SM too.

There is a dive that is near Kingston/Cornwall ON which I have been suggested to dive doubles. So, I am considering doubles.

Air consumption is not the issue. I could be on a rebreather and still suck it back faster than many. That will get better the more I dive.

I want to dive with a guide as I do not know the cave systems. If a friend of mine knew them and invited me to dive with them, then I like would, but they are still a guide.

Other dives likely do not need doubles/SM.

What dive site is that...Kingston to Cornwall is a very large area

 

[swimmer_spe]

What dive site is that...Kingston to Cornwall is a very large area

At this point, I don't remember. It was sometime last summer. I would have to go through all that I have posted.

 

[shoredivr]

At this point, I don't remember. It was sometime last summer. I would have to go through all that I have posted.

Was it a deep wreck or a drift dive?

 

[swimmer_spe]

Was it a deep wreck or a drift dive?

It was a long swim.