Steel tanks & wetsuit - some real experience to go with the claims....

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are -1.5 each, with the stock valve. Doubled they're about -3 + the bands, or -5 or so total, when empty.

I had 500 psi in them when I started my weight test, and was about a pound or two heavy with the wing empty. I had ~2.3lbs of air in the tanks. That means the rig was almost EXACTLY neutral with no gas at the surface in a 3 mil wetsuit - for me.

We got blown out this morning, but we're going tomorrow AM - I'll post my results in the evening when I get in..... If I don't post tomorrow night then you'll know that I sunk like a stone :)
 
Ditching isn't *ALWAYS* bad!

Genesis once bubbled...
.. I believe that ditching at depth (.vs. on the surface) is a poor choice in nearly all cases....

First of all, I highly commend you on doing your own analysis of what's going on, regardless of what anyone else says. Ultimately, you are responsible for your own life, regardless of what anyone else recommends.

Having said that, I disagree that ditching at depth is *never* the right solution. I've read most of your posts regarding ditching on DB the last few months, and I agree with most everything you've said.

Ditching a *LOT* of weight at depth and turning yourself into a Polaris missle is not a great solution if there is a better solution to be had. (And, we're having this discussion to see if there is a better solution.)

One of the solutions you've thrown out is using an AL plate, which gives you 3# of ditchable weight. I'd like to see more like 4-6# of weight with doubles, but I think ditching that much weight (at depth) is not the end of the world.

Heck, if you can swim UP 22# of weight, then you should be able to easily swim DOWN the extra 6# of buoyancy (worst case) you're going to have as you approach the surface.

Ditching a few pounds of weight isn't going to cause you to become a missle, and unless you're completely out of air and have no air left in your tanks, the loss of a few pounds will still allow you to control your ascent.

At the two extremes we have way too much weight at the beginning of a dive. Losing your wing at this point is *VERY* bad, and is probably the most likely time for it to occur. (Forgot to turn on the tanks, forgot to hook the inflator hose, the wing snagged and ripped off entering the water, it didn't work and you didn't realize it until after you're in the water, etc..). Dropping 6# of weight at this point would still require you to swim up your rig, regardless of where in the water column you're at since you'd be negative. Ditching is a good thing here.

At the other extreme, we're going to assume somehow you've lost your wing at the end of the dive. Again, this is *much* less likely simply because generally speaking, usually things break when they're first used. However, Murphy would tell us otherwise, so we'll plan for it. Somehow we screwed up, and we've got just enough air to get to the surface (assuming we have to work our tail off). At this point, we're no longer 22# negative. There are two solutions at this point.

1) Don't ditch the weight, and swim up the rig. Heck, assuming we've done a dive, we're no worse off than we were at the beginning of the dive when we chose to ditch the weight last time this happened.
2) Ditch the weight. (Note, if we can handle dropping weight at this point, then we should be able to handle dropping weights at *any* other time during the dive, since at this point it will make it the hardest to deal with)

So, instead of -22# at depth, we've lost 15# of gas, so we're at -7#. If we ditch the weight (let's say 6#), we're still at -1#, which is easily managable. Unfortunately, the -1 is going to end up at +9 at the surface (due to wetsuit compression adding 10# of buoyancy).

I guess I'm of the opinion that if I can swim *UP* 22#, I can pretty easily swim *down*, or more realistically, slown down my ascent even with +9# of buoyancy.

Again, doing a risk analysis, I believe the most likely chance of failure is at the beginning of the dive. Ditching a small amount of weight at this point I would not only say is acceptable, but optimal. (Again, the amount of buoyancy change would be far less than the shift due to air consumption). This is *ESPECIALLY* important of you've got no bottom, or the bottom is deep enough to be unsafe for your mix/training.

At the end of the dive, even those there is the risk of becoming 'overly buoyant', you can offset that risk by either not dumping your weightbelt, or by understanding that the loss of weight will cause buoyancy issues, but these issues can easily be overcome by swimming down to slow your ascents to a managable.

(I'd argue that one should feel comfortable with ditching the weightbelt in *ALL* situations, since if you're in a bad situation, task loading will be hard enough that you don't want to have to determine if you've got enough 'air' in the tanks to offset the loss of the ditched weight.)

Feel free to flame away where I've missed out on some important detail!


Nate
 
is that when it becomes a problem you're low on gas.

That is precisely when fighting to stay down is bad, because your supply is limited.

Otherwise, I agree. But if I can swim up the rig, or find an alternative (such as a bag) to a completely dead BC, then I think I prefer that.

I'll post more after tomorrow when I dive 'em....
 
Did two dives on my new doubles set today.... twin Hp100s.

I've got some work to do with the position of the bands and where the wing is. I was butt-light on the first dive (full), and butt-heavy on the second (half full at start), which was pretty bizarre. . You get the opposite shift with ALs and to some extent with single HPs, but not with the doubles. I think the bands need to be moved up on the tank (I'm about an inch or a bit more below the break; I think I need to come up about a half-inch or so. I had the wing on the bottom set of holes (up as far as it could be set) so the only way to get more "offset" is to move the tanks down. That shouldn't cause valve access trouble.

(Does that make sense in terms of which way to move the bands and wing? I think I've got the mechanics right on this....)

I also discovered that the "fit" of the plate harness is WAY more important. I had just replaced the webbing, and it was too loose on the first dive. Adjusted that, and it was much better on the second.....

As for swimming up the twins from 130', not with the Quattros. But I also attempted to salvage a lost anchor, which was about the same weight as my anchor, and there's no way I could swim IT up with the Quattros either. With the Twinjets I'd have been able to do it - so its lift bag time for me (which I had with me) if I dive these wet with the Quattros - but not by much. With the Twinjets, even though I know they're "devil fins" according to many, I'm sure I could swim them up. Then again blades have always been a bit "strange" as fins for me...

Reboarding was nowhere near as tough as I expected, nor was gearing up.

The "big deal" was trim, and I suspect that with adjustment to the band and wing position that is readily solveable.

With the two dives, even with my gas consumption a bit higher than my usual (about 0.5 for SAC) across both, I still did both dives and had a third of my original gas remaining. I could have conceivably done a third today, but we ran out of daylight.

It is like learning to dive all over again though from a trim perspective...

More bubble time to follow...
 
If you can't swim that rig up, then it sounds like you're using the wrong gear.

It sounds to me like you'd be better off with a set of double AL80's on a steel plate.

Or, dive dry.

I'm not a fan of leaving it up to a proper lift bag deployment to save my life. What if you drop it during deployment?

Even if it's done correctly, it'll still take all sorts of precious time to get deployed... And you'll still have the problem of being submerged in like 5' of water when your bag hits the surface. Of course, by then you'll have more buoyancy in your suit, but you get the drift...

You know, Gen, right about now I could point out that all of this thought and conversation and experimentation could have been avoided if you'd just believed what DIR was teaching... That as a general rule, AL80's should be used when diving wet...

Would you like a glass of Kool-Aid? :D

Of course, I'm just teasin' ya, bud. :D
 
You might want to put the bands right up to where the tanks start to round over. I only have one set of holes in my Explorer wing so that part is easy for me. :D
 
THanx for takin' the time to try all these different configurations and report back.I'd be interested to see how much actual bouyancy is lost in a wetsuit at depth.It would take say increments of #1 at mebbe the surface and at 100'or a stainless fishscale tied to an empty suit a the same depths.I often see divers overcompensate for wetsuit bouyancy.Never good to be heavier than you can lift with your BC and tanks full but I see it.
 
I had the bands about a half inch from where they start to round over on my LP80's and ended up moving them the extra half inch down.
 
I may as well just use the Twinjets :) I know I can swim that rig up with them on my feet, and will test it once again shortly (as soon as the weather stops blowing - its supposed to be ugly this coming week)

The bag is easy - I DID try that. Slip the strap over the left arm, then inflate. With very little gas in there I can easily swim it up. That's not coming off during deployment. And this IS only to cover the one-in-a-million shot of the BC being totally hosed at the start of the dive, with a maximum mass of the gas.

This was the first time I really made a "maximum power run" with the Quattros, and I was shocked at how much weaker they are than the Twinjets when you really have to put the coal to them. I had run into issues with currents before, but this was the first time I could quantify it - and trying to lift that anchor was enough for me to be able to quantify it. The thrust difference has to be at least 30% - and perhaps more. Since I HATE Jetfins, and the Quattros I can deal with but they just don't do it in terms of power, I guess I either have to learn to live with the Quattros or just dive the Twinjets :)

Will move the bands this week since I have to dump to refill anyway (my O2 bottle isn't full enough to mix on top of what I've already got)

Twin AL80s are going to make me MAJOR butt-light when they get drained. I suspect I'd be REAL unhappy with the trim in those... probably beyond what I can fix with band and wing positioning.

More as I know more.... this is an interesting exercise, and I really like not banging my head on the tank or valve diving the doubles.

BTW, the dreaded "turtle stuff" wasn't a big deal. Yeah, I could get "overcenter" too far and roll on my back, but it was easily recoverable. No problem there of substance.
 
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