doubles in DIR diving wet....

[SparticleBrane]

To be honest, if the tanks are filled as El Guapo recommends you shouldn't have any issues...

 

[TSandM]

I think you can make the argument that there is a "need" for training with any equipment. A superb diver I know was out tonight diving in 30 feet of water, practicing moving multiple deco bottles around. Was it wrong for him to take that gear into shallow water? Of course not!

I have been diving my doubles all the time since last November. Why? Because the fellow who taught my wreck workshop, who is Cave 2, told me he thought I should dive them exclusively until I got better at managing them, in and out of the water. I have a goal, which is Cave 1 next spring, and I take those tanks into the water each time with that goal in mind. That's legitimate.

But you don't HAVE to dive doubles to be DIR on a dive -- Is anybody going to argue with me on that point? I think a lot of people get the idea that ALL DIR diving must be done with doubles and stages and scooters, and it simply isn't so. Many recreational dives are safely and appropriately performed with a single tank rig, and if I ever get competent and strong with the doubles, I'll go back to using a single tank for those dives.

 

[TSandM]

Am I correct, or is it now DIR to dive without analyzing?

"Always analyze your own gas."

But how many of us analyze both posts? It's a legitimate issue to bring up, to point out to the new doubles diver that, especially if you are not sure the isolator was open while the tanks were filled, it doesn't hurt to analyze both posts.

I don't think anybody here has given non-DIR advice, in the sense that no one has advocated a non-DIR answer. DIR teaches to analyze your gas. Pointing out that an isolator creates the possibility of some strange gas content problems is not "not DIR".

 

[ekewaka]

"Always analyze your own gas."

But how many of us analyze both posts? It's a legitimate issue to bring up, to point out to the new doubles diver that, especially if you are not sure the isolator was open while the tanks were filled, it doesn't hurt to analyze both posts.

It is best to analyze both posts, but you should be able to find the problem by analyzing only one. If the O₂ is high on one side, then it will probably be low on the other. Analyze either of them and you will know there is a problem.

I don't think anybody here has given non-DIR advice, in the sense that no one has advocated a non-DIR answer. DIR teaches to analyze your gas. Pointing out that an isolator creates the possibility of some strange gas content problems is not "not DIR".

Maybe I misunderstood. I thought some were saying that it was better not to use doubles because of the danger of not analyzing. If they were only recommending analyzing both posts, then I agree.

 

[limeyx]

I am talking about Worthington steels, not Fabers. I don't recommend Fabers to anyone. Also note that the Worthingon (and apparently the Faber) are listed with their freshwater figures and the AL80 with its saltwater figure. In freshwater the AL80 is about 3# negative. So the net difference to the Faber is 3.7# per tank or 7.4 total pounds with doubles. I dare say that for most divers, unless they are diving doubles in the tropics, they could remove some lead and close the gap of that 7.4# to nearly nothing. I know in my case, I could drop the 4# tailweight so now we're at 3.4# of difference. And I could dump my steel backplate for teh kydex one I want which is about a 3.5 pound difference. So my net is essentially zero.

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.

 

[limeyx]

wrong.

thanks for your o so enlightening comment.

 

[Soggy]

This shouldn't be a problem because we always analyze our gas before we dive. Am I correct, or is it now DIR to dive without analyzing?

The point is that you need to analyze both posts.

 

[JimC]

It is best to analyze both posts, but you should be able to find the problem by analyzing only one. If the O₂ is high on one side, then it will probably be low on the other. Analyze either of them and you will know there is a problem.

Not if your target mix is 21/35 and there is air in one side and some random helium/o2 mix in the other. Unfortunately, if that random helium/02 mix in the other side just HAPPENS to come out to 21/79.. you're damned even if you analyze both posts.

 

[Soggy]

Not if your target mix is 21/35 and there is air in one side and some random helium/o2 mix in the other. Unfortunately, if that random helium/02 mix in the other side just HAPPENS to come out to 21/79.. you're damned even if you analyze both posts.

That is solvable with either a helium analyzer or the Mickey Mouse(tm) test.

 

[RTodd]

I am not sure the 85's with a wetsuit are a good idea.

Luxfer AL80 is -1.4 full, +4.4 empty
Faber LP85 is -6.7 full 0 empty

so you will need 8.8 pounds less weight on the fabers, but also be 8.8 pounds more negative at the start of the dive (maybe a little more due to more gas)

so unless you need a lot of ditchable weight with the AL80s (unlikely in a 3mm suit), you are (probably) going to be too negative in the steel tanks to swim it up.

To add to this since some don't seem to get it, LP 85s are 6lb negative at 2650. But, they are often filled to 3500. One of the geeks can do the math and get the real numbers, but back of the envelope puts you at around 16lbs negative in doubles at the start of a dive. While many could swim that up while wearing a 3mm wetsuit, it isn't exactly a rig you could comfortable hold a stop in. While LP85s may be okay for some wetsuit applications, AL80s always work and give you the option of adding ditchable weight. Unless you are going to have a garage full of doubles (guilty) or are only diving one of the specific applications where LP85s work, you are better off with double Al80s for wetsuit diving. For single tank diving, LP85s have a wider range of use. But, Al80s are still the most versatile.

And back to the original issue. Practicing with doubles in 40' if you are experienced enough to be getting ready to move to a level where you need them is not unrealistic. (The original poster is not anywhere near that yet.) However, just going diving and getting your bouyancy spot on accomplishes 95% of what you need to know to dive doubles anyway. Doubles are easier to dive in a drysuit because they balance your weight better. If your bouyuancy and other skills are all dialed in, it really only takes a few dives to get comfortable with doubles.