doubles in DIR diving wet....

[PerroneFord]

The question is, can you swim it up? If you can indeed swim up the AL80's full w/out ditching any weight now, and you can then go to an AL plate and ditch the tail weight and still be balanced in the 85's then it might work.

However, a lot of people use the AL80's in order to gain some ditchable weight. If you "ditch" the ditchable then with the 85's, you may not be able to swim it up.
Obviously there is some margin here as some people inherently seem to need less weight than others (I always seem to use more than my buddy even though he is heavier than me).

I do indeed swap out about 4 pounds of lead when going from an AL80 to a faber LP85

With a single 85 in a 7MM wetsuit, I need a steel plate and 8 pounds of lead.

What is this fascination with ditchable weight? I dive in caves. Ditchable weight is meaningless. It's meaningless for decompression diving as well. Last thing you want to do on a deco dive is LOSE ballast. Dive a balanced rig. Problem solved.

 

[RTodd]

What is this fascination with ditchable weight? I dive in caves. Ditchable weight is meaningless. It's meaningless for decompression diving as well. Last thing you want to do on a deco dive is LOSE ballast. Dive a balanced rig. Problem solved.

Because when you have 15-20lbs of gas or more on your back, when you lose your wing on the dive dictates how much weight you will need to get to the surface and do any stops. It is still a balanced rig. In a 3mm, the weight I am carrying is basically to offset positive al80s when near empty. If the dive goes sideways early on, I may want to ditch some weight to make any stops more comfortable. With Al80s, you have this options plus the gas swing is less (lower volume) and the problem is less magnified.

That is why the two DIR choices for cave diving are, in general, a wetsuit and al80s or a drysuit and steel tanks. As noted before, depending on the depth range and wetsuit thickness, 85s might work with a wetsuit. But, hard to lay that out as a general rule.

 

[Soggy]

Another thing to point out is that diving a *thick* wetsuit and doubles is generally not the best idea, since you will require a substantial amount of weight to get below the crush depth of the suit, but below that you will be incredibly overweighted. Like everything, the exact situation might change things, but a drysuit is definitely preferable over a 2 piece 7mm wetsuit.

 

[Randy43068]

You're right. There is nothing dangerous about diving doubles. Nobody ever died from carrying too much gas.

If I was just starting out I would go with AL80s doubled up because they can be broken down into singles later for use as stage or deco tanks.

People around me die, or want to when I have too much gas!

 

[JeffG]

It's meaningless for decompression diving as well. Last thing you want to do on a deco dive is LOSE ballast. Dive a balanced rig. Problem solved.

A balanced rig may entail having ditchable weight.

The holy grail of the balanced rig. LOL.

 

[Randy43068]

Another thing to point out is that diving a *thick* wetsuit and doubles is generally not the best idea, since you will require a substantial amount of weight to get below the crush depth of the suit, but below that you will be incredibly overweighted. Like everything, the exact situation might change things, but a drysuit is definitely preferable over a 2 piece 7mm wetsuit.

Take it from me.. thick wetsuits are really tough to control when trying to maintain good buoyancy and changing depth a few feet. Too much expansion and compression going on. My GUE instructor said that anything over a 3mil is too much neoprene and I should be using a drysuit in those conditions. I have to agree...

 

[JeffG]

The point is that you need to analyze both posts.

I have never analyzed both posts, but then again. 99.9% of the time, I am mixing my own gas. (or standing beside my tanks at the time of filling)

 

[Clare]

What is this fascination with ditchable weight? I dive in caves. Ditchable weight is meaningless. It's meaningless for decompression diving as well. Last thing you want to do on a deco dive is LOSE ballast. Dive a balanced rig. Problem solved.

Perrone - achieving a balanced rig for ocean diving may require you to have ditchable weight. I've had a complete wing failure with three full stages and a full set of back gas - it's not that big a deal with a switched on team but proves it can and does happen. When faced with that ditchable weight is a nice to have

Be careful also of presuming that all steel tanks present weighting problems. The ones we use in Europe are almost neutral when empty so don't give the same problems. In comparison the 104s I wear in Florida leave me so negative with no weight at all that I can't get comfortable on the surface and have to wear extra undersuits to compensate.

Wetsuits are clearly not an option in caves or at home in the UK but in the Red Sea with a wetsuit I have dived twin Ali 80s - with an ali plate and a small weightbelt that I can ditch if necessary.

For training in how to use a twinset (and how to analyse your gas) I'd recommend GUE F. If you contact your local instructor he/she will talk you through the kit choices and help you reach a decision which will suit your diving.

HTH

 

[Soggy]

I have never analyzed both posts, but then again. 99.9% of the time, I am mixing my own gas. (or standing beside my tanks at the time of filling)

If you are filling your own tanks, you have more control. Most of us have to drop our stuff off. I just make it habit to always check both posts before diving. Better to be safe and waste an extra 30 seconds of time than dead.

 

[PerroneFord]

I certainly don't disagree, but in my ocean setup for diving here, with twin AL80s, a SS Backplate, and no additional weight, I am already negative. Everyone won't be in that scenario, especially if they wear more neoprene. But honestly, we should only be negative in the ocean, by the weight of the gas, and if diving wet, the amount of lift lost due to compression of the suit. In a thick wetsuit, you could lose 10 pounds of lift in compression (or more) and your gas is 12#. So you could potentially face being 22# negative with just the doubles.

This is one reason I am not a huge fan of thick neoprene and doubles.

Perrone - achieving a balanced rig for ocean diving may require you to have ditchable weight. I've had a complete wing failure with three full stages and a full set of back gas - it's not that big a deal with a switched on team but proves it can and does happen. When faced with that ditchable weight is a nice to have