Single Cylinder vs. Doubles

[padiscubapro]

I don't know of ANY boat that doesn't count isolated manifoled doubles as a redundant gas supply.. I havent ever been not allowed to dive on any boat NY or NJ...

My point was that the gas capacity of twin 95s is huge.. You could do it with 80s it would still work but I don't like the characteristics of al 80s.. at the proposed RMV you would need 90cft of gas for each dive of 30 minutes, so obviously an 80 wouldn't cut it.

I used a high rmv since you are most likely a new diver.. I can easily get 1 hour total dive time at 100ft and still have lots of reserves..

My RMV is around .5 cft/min at the surface, so at 100 it would be 2cft per minute, 60minutes uses 120cft of 190cft in total.

with an overfil to just 3000psi I could get (3) 30 min dives to 100 and have 36cft of gas left.. I'd be starting with 216cft of gas and would be on board after the last dive with 500 PSI in the tank which still meets the thirds rule and then some...

 

[jamiei]

i have a scubapro classic NT and was wondering whats the best way to rig it (if possible) with double tanks. I believe it has plenty of lift (@60 lbs) for doubles, but haven't gotten into using doubles yet and want someone elses advice. I've seen some sort of kit with a bracket that attaches to the vest and it gives the options of either sliding in a single tank or double tank bracket.

 

[Scubaroo]

jamiei once bubbled...
i have a scubapro classic NT and was wondering whats the best way to rig it (if possible) with double tanks. I believe it has plenty of lift (@60 lbs) for doubles, but haven't gotten into using doubles yet and want someone elses advice. I've seen some sort of kit with a bracket that attaches to the vest and it gives the options of either sliding in a single tank or double tank bracket.

Doubles and jacket BCs don't make good bedfellows... a set of doubles is going to weigh close to 90 pounds on land (or more for larger tanks) - you want something that can handle the weight OUT of the water. Look at backplates. Also look at "technical" BCs. Then take another look at backplates

 

[jamiei]

whats the problem with using a backplate with the bcd? i was thinking of using two alum 80's that weigh in at @35 lbs each. If that won't work, what about an 80 and a 40 with its own reg... any recommendations on a cheap backup?

 

[Scubaroo]

Does the Scubapro Classic NT take a backplate? I don't think it does... seriously, look into backplate/wings, or back inflation BCs designed for doubles.

Even if you've got twin aluminum tanks - are you going to put them in SS bands and manifold them? Adds weight, as does the twin first stages.

What is your reasoning for wanting to dive doubles? I've only just started, and it was because of a specific need for types of diving I wanted to do (deep dives and a wreck course that required additional gas and redundancy).

 

[techdiver2us]

Here's my input, despite whatever I normally use. I was asked by a dive operator in Curacao how deep I wanted to go. Keeping in mind my SAC rate and experience I said 150'. The dive and deco were completed with 800psi left, so I consider it was a fair estimation. On the other hand this divemaster told me he'd done 220' equipped as we were with a single AL80. I had to tell him I thought he was taking too great a risk, especially since he described having symptoms of oxtox. At any rate everyone is different. I wouldn't have considered doing 150' during earlier stages of my diving. And as to what I normally dive - doubles, and if I end dive with less than 1000 psi I figure I blew my plan.

 

[boomx5]

techdiver2us once bubbled...
On the other hand this divemaster told me he'd done 220' equipped as we were with a single AL80. I had to tell him I thought he was taking too great a risk, especially since he described having symptoms of oxtox.

That sure seems like a whole lot of risk. It's beyond me to think someone would take that kind of risk with their life.