Steel vs aluminum 40 for redundant: which is better?

[coldwaterglutton]

Yeah not my rules on the boat so I am stuck.

Unfortunately at this point I am too old to carry the double steels as I used to in my youth. As for my son, he's not penetrating any of these wrecks - which is a bad idea on the San Diego, absolutely verboten on the U-853, and not necessary on the Oregon - so a carry bottle is best. But the point on training is well made, and I had already planned to run a malfunctioning air exercise with him at the Mandy Ray for exactly that purpose.

When I used to dive the Mandy Ray 20 years ago, just after she was sunk, I did it with a buddy off my own 18' boat on a single aluminum 80. It was one of the places I could reliably spear a nice striper every time and I really enjoyed it.

 

[Nick_Radov]

Yes, slung is a more accurate description.

And it's not an agency requirement but a dive boat requirement. Pretty much standard for the NY/NJ dive boats to require redundant, or isolation manifold for doubles, etc. Plus it's also a very good idea.

Just background, taking my younger son to the Mandy Ray @85' to make sure his salt water buoyancy and trim are optimal. Then we are hitting the Oregon, the San Diego and U-853 over the summer. These are all deep wrecks by recreational standards. He has decent northeast experience but at shallower depths and hasn't yet carried a redundant tank. I myself have an aluminum 40 with my old Titan on it that I've carried for quite a while.

Regardless of stage tank material, this isn't an ideal rig for a deep-ish dive like the U-853. You and your son would be better off with proper isolation manifold doubles — plus the training to manage failures. Are you looking to satisfy an arbitrary dive boat rule or do you actually want to be safe and comfortable on the dives?

 

[grf88]

Why is it that almost every time someone talks about using a pony as a fully redundant system somebody comes on and suggests they replace it with a system that is not fully redundant. The isolation valve on manifolded doubles means they are not a fully redundant system as it's failure, although rare, means that it is not fully redundant.

 

[coldwaterglutton]

Regardless of stage tank material, this isn't an ideal rig for a deep-ish dive like the U-853. You and your son would be better off with proper isolation manifold doubles — plus the training to manage failures. Are you looking to satisfy an arbitrary dive boat rule or do you actually want to be safe and comfortable on the dives?

I'm not sure I agree with that and many divers I've gone with - far more experienced than me - dive on single tank and pony. On 27% that's a 12 minute no-deco limit and I find I have plenty of air when back up top. No need to schlep doubles for that kind of affair.

 

[boulderjohn]

I meant if he ends up using the tank it won't go positive as an aluminum one, but it's all relative.

This is one of the most common misunderstandings in scuba.

A diver's buoyancy during a dive depends upon the relationship between the diver's total volume and the diver's total weight. The weight and volume of the individual parts of the diver and gear only matter in how they contribute to the total weight and volume.

If a diver breathes two pounds of air out of a scuba tank during a dive, the diver's total weight will be two pounds less, but there will be no change in volume. That makes the diver two pounds more buoyant. It does not matter whether the tank it was in is aluminum or steel. The only difference is the loss of two pounds of air.

 

[mr_v]

Why is it that almost every time someone talks about using a pony as a fully redundant system somebody comes on and suggests they replace it with a system that is not fully redundant. The isolation valve on manifolded doubles means they are not a fully redundant system as it's failure, although rare, means that it is not fully redundant.

Because more often than not the desire to use a pony bottle implies other underlying issues like not being comfortable with the gear, dive plan, buddies, or statistics (there is little correlation between gear failure and fatalities).

This thread is an exception - the OP must comply with some obscure boat rules - but it does not change the fact that doubles or sidemounted configurations are better long-term options for solo or self-reliant diving.

I'll flip your question back at you: why does someone always advocate for a pony bottle when there are better solutions?

 

[Nick_Radov]

Why is it that almost every time someone talks about using a pony as a fully redundant system somebody comes on and suggests they replace it with a system that is not fully redundant. The isolation valve on manifolded doubles means they are not a fully redundant system as it's failure, although rare, means that it is not fully redundant.

We have to look holistically at the entire system including the integrated team, not just at individual pieces of gear. Your dive buddy provides your full redundancy. An isolation manifold maximizes your options for preserving breathing gas under the most common failures.

While in theory a manifold does represent a single point of failure, in practice you're more likely to be struck by lightning than to lose all your back gas from a broken manifold. What seems to make sense in an online discussion doesn't necessarily work well in real diving.

 

[grf88]

Because more often than not the desire to use a pony bottle implies other underlying issues like not being comfortable with the gear, dive plan, buddies, or statistics (there is little correlation between gear failure and fatalities).

This thread is an exception - the OP must comply with some obscure boat rules - but it does not change the fact that doubles or sidemounted configurations are better long-term options for solo or self-reliant diving.

I'll flip your question back at you: why does someone always advocate for a pony bottle when there are better solutions?

As I pointed out manifolded doubles do not provide full redundancy so is not a better solution to redundancy but obviously has other uses.. Adding a side lung pony is the simplest way to achieve full redundancy as will side-mount or even independent doubles but with added cost and complexity. Personally I dive side-mount, doubles and single tank and for recreational depths usually use either side-mount or single back-mount with pony. Whichever way I dive I make certain I am fully redundant as the idea that your emergency gas should be on the back of your buddy is, to me, an asinine idea. Why the suggestion that keeps arising that people who choose a pony somehow do not know what they are doing or are not competent is frankly insulting.

 

[mr_v]

Insults are taken, not given.

 

[coldwaterglutton]

I wouldn't rely on a buddy for backup air in the cold, dark and gloomy conditions here in NY. I've been one more than one dive -- especially in the Long Island Sound -- where I had to stay in physical contact with my buddy but couldn't see him even though I was holding hands with him. (The Gwendoline Steers is the poster child for this, viz there varies from 10 feet to 12" depending on the day)

But it's also why I take a 40L pony and not one of the smaller sizes. If I need to get into it, I need enough air for a controlled ascent and safety stop.