DIR- Generic Fundies as a first encounter with doubles

[Lorenzoid]

My issue may have something to do with the fact that by the time I took up doubles and drysuit, I had done over 200 dives in an Al 80 and 3mm wetsuit. I was like a dolphin. With a drysuit, steel doubles, and larger wing, I feel like a whale. Not what I’d call nimble at all.

 

[EireDiver606]

My issue may have something to do with the fact that by the time I took up doubles and drysuit, I had done over 200 dives in an Al 80 and 3mm wetsuit. I was like a dolphin. With a drysuit, steel doubles, and larger wing, I feel like a whale. Not what I’d call nimble at all.

That’s totally fair enough. It’s probably more of a psychological “you know what you’re used to” type thing. If you feel like a whale with doubles, the guys who do wkkp exploration dives are like oil tankers

 

[EireDiver606]

It is not subs have two tanks, we have two tanks, so we are stable. Subs shift water between their tanks. You do not normally pump air between doubles to adjust their mass.

And stability is a bit more about having ballast low. Plus subs have more than two ballast tanks. Plus trim tanks, fore, aft, port, starboard. And compensating tanks near the center.

ETA: I have now reordered the sentences of my above paragraphs for clarity. Without changing their content. Putting the crucial difference first, then extra other issues later.

View attachment 537670
Submarine Design: Unique Tanks On a Submarine

Now, if you want to talk about subs move mass and are stable. We can move mass/lead. Could that make us stable?? That would be an analogy that would work.

Quoting from that piece:
"Trim tanks are used to maintain the longitudinal center of gravity just under the center of buoyancy, so that the submarine can be maneuvered to a neutral trim condition."

Im not suggesting twin tanks made stability, I said that the greater surface area makes it more stable as more water has to be moved to ascend / descend. One of the main reasons why good divers have good trim and buoyancy is because of this, it allows them to have more time to expect changing buoyancy.

Edit: I know why you’re confused @MichaelMc . I’m not saying that the cylinders of a double tank configuration make stability but it is the fact that there is two of them and they create a greater surface area. Does that clear things up?

 

[MichaelMc]

Im not suggesting twin tanks made stability, I said that the greater surface area makes it more stable as more water has to be moved to ascend / descend. One of the main reasons why good divers have good trim and buoyancy is because of this, it allows them to have more time to expect changing buoyancy.

That is not what you said.

You said the below, which does not reference anything about drag.

Words of wisdom right here. Don’t be intimidated is right, I used to think that doubles somehow “technical” and that’s just plain wrong. That sort of mindset isn’t good for progression. I’d say it takes only max 20 dives to get comfortable in doubles. For me it took more like 5. So much more stable. And if you think about it, a submarine has two ballast tanks for stability so why shouldn’t a diver have the same? Do the doubles first in a wetsuit, after a couple dives, try the drysuit.

If you feel now the issue was drag, a sub dividing its insides to have two tanks vs having one or five has no affect on its drag. So claiming your "subs, two tanks, us, stability" was about drag makes no sense. It is just bizarre. As is your above good divers have good trim and buoyancy because of their drag. Bizarre.

You are saying things which I can tell are plainly bizarre just as they are written. Which leads me to question your other statements that I can not judge just based on what you have written. I have no comfort in believing they are not equally as bizarre.

 

[EireDiver606]

That is not what you said.

You said the below, which does not reference anything about drag.


If you feel now the issue was drag, a sub dividing its insides to have two tanks vs having one or five has no affect on its drag. So claiming your "subs, two tanks, us, stability" was about drag makes no sense. It is just bizarre. As is your above good divers have good trim and buoyancy because of their drag. Bizarre.

You are saying things which I can tell are plainly bizarre just as they are written. Which leads me to question your other statements that I can not judge just based on what you have written. I have no comfort in believing they are not equally as bizarre.

Momentum on doubles? I’ve never found a notable difference but maybe you could be right. My understanding is that greater surface area (in trim of course) means slower ascending/ descending since it has to push a bigger body of water out of the way. While the wing is about 10lbs bigger so yes it will have 33% more lift compared to singles which means 33% more gas can expand when ascending.

That’s what I said earlier.
Please stop arguing semantics. You’re overthinking it.

 

[MichaelMc]

That’s what I said earlier.
Please stop arguing semantics. You’re overthinking it.

I'm done here.

 

[Ayisha]

I would not go into a class with a new piece of gear. You’ll waste time and could be distracted by making gear adjustments that should have been resolved before class.

Switching to doubles is relatively easy, but there’s still an adjustment period. You may need to fine tune your buoyancy, adjust your harness, etc...

I completely agree. IMHO a Fundies class is not the best place to try out any new significant equipment if you actually want to experience the full skills development of the class. Having helped out in a Fundies class where one student dove doubles for the first time, a second student dove doubles for the second time, and the clincher, a 3rd student dove with a 7mm 2 piece wetsuit, hood, gloves, bp/w and long hose for the first time, each of the students had a large learning curve in buoyancy and trim, weighting, adjustments, maintaining static trim, and controlling graduated ascents/descents.

Two of the students required excessive one on one training, which, again IMHO, was unfair to other students who could not progress to the rest of the required skills. It's not the first time I've seen new gear hold back an individual or a class and the majority of a class is spent on basics.
(In that case, the Instructor added dates at a later date to complete the course, but that isn't always going to happen - for free).

I think if a course is coming soon, it's much better to do Fundies in gear that you're comfortable and squared away in. You can always upgrade to a tech endorsement later. If you've given yourself time to practice with doubles (or other significant gear) before Fundies so that your weighting, equipment adjustments, buoyancy, trim, and control are reasonable, you'll get the most out of the course and have more time to progress through all the required skills.

 

[rjack321]

I would take the advice of your instructor. Basically you get a doubles primer & fundies in one. Doubles are generally considered fairly easy to dive once trimmed out and you'll get help with that. Valve drills can be a challenge but you'll get help in class there too.

 

[KevinNM]

I’d strongly suggest that whatever path you use, have the first time you try to do a doubles valve drill that you do it with a GUE instructor. It’s reasonably complex and has to be done exactly right. Bad habits developed here are a problem. It’s also very helpful when the instructor stops you from turning off all your gas under water when you mess it up. Which I tried to do in a fundies class.

 

[Lorenzoid]

. . . It’s also very helpful when the instructor stops you from turning off all your gas under water when you mess it up. Which I tried to do in a fundies class.

It has been said that it's not a matter of if you will turn off all your gas during a valve drill, it's a matter of when. I have done it more than once, and it's a good thing my similarly trained teammate was facing me, paying attention, and ready to donate, as one is supposed to be during a valve drill.