SeaJay, I'll agree that steel tanks will get rust spots, and will leave marks on fiberglass boats. That's why I have rubber mats in my boat. But it is a VERY rare diver here in Puget Sound who dives Al80 single tanks for very long -- they just don't make any sense here. Steel tanks are almost ubiquitous in the Pacific Northwest -- in salt water. Only in warm salt water do Al80s make sense.
Why? I've never dived the Pacific Northwest, but I can't imagine that it'd make any difference as far as corrosion rates go...
Yeah, I just put DriDeck in a couple of my boats. I liked it so much that I put it in the shop, too... But that's not really a solution for corroding tanks - that's more like a Band-Aid for the symptom, isn't it?
What makes diving steels in the Pacifc Northwest different than diving steels on the East Coast?
And finally, if you are doing a sub-30 meter dive, I hope you have at least 100 cubic feet of gas on your back. If you are weighted to be neutral with an EMPTY tank, you will be 7 lbs NEGATIVE at the beginning of the dive from the gas you are carrying.
Okay, sure, with a 100 cuft tank instead of an AL80, yeah.
At the end of your descent, you will still be 7 lbs negative from gas, but you will now also be 20 pounds negative from buoyancy loss in a heavy wetsuit, or 27 pounds negative.
I certainly hope not! What kind of 7 mil suit are you guys diving that compresses 20 lbs? What kind of 7 mil suit are you guys diving that compresses an ADDITIONAL 20 lbs from 15 (since that's the point at which you're neutrally weighted) to 100 feet?
If at this point you pull the inflator hose off your BC while attempting to use your pull dump (which happens!)
Yeah, I know... I've done it, too.
One of the many reasons I don't recommend pull dumps, by the way.
you are on the bottom with a BC you can't put any air in and that won't hold any of what's in it if you are at all head up. At this point, you'd better have weight to ditch, or redundant buoyancy.
...Or dive horizontal in the first place and not even notice that you've pulled your pull dump out.
That's how it happened to me. I didn't know I'd done it until I was on my way up to the surface, and a few feet from the surface I turned "head up" and couldn't inflate my BC. Wow, that was like 10 or 12 years ago now...
Feels like yesterday.
Anyway, I didn't have to ditch - primarily because my tank was empty, and I was therefore almost perfectly neutral. I kinda went, "Aw, man..." and swam over to the boat and got in and tried to figure out why I'd pulled the dump off.
At least, that's how it happened to me - maybe your experience has been different.
I know, and you know, that the better solution is NOT to be at 100 feet with a heavy wetsuit. But telling someone never, ever to pull their weights at depth could result in an avoidable fatality.
I did a body recovery once of a guy who was diving with 108 lbs of lead... No joke. He had one of those weight "harnesses" in addition to a slew of weight in the pockets of his BC (non weight integrated). He even had one weight IN his wetsuit. His buddy later told me that he'd dropped it down his neck hole just before splashing in "for good measure."
Why did this man die? He died because he ran out of gas. He was in 28' of water, with no overhead.
I wasn't there to see him die, but I can tell you based on what I pulled out of the water that I know exactly what happened. He breathed a "sucking" breath, and when he realized he was empty, he squeezed the power inflator. He might have gotten a couple of seconds' worth of gas to go into his BC, but that was it... And now he was say, some 85 pounds negative and with no gas.
Naturally, he should have dumped his gear at that point. Unfortunately for him, it took too long to get his BC and rig off (perhaps because it weighed so much) so that he could remove his weight harness (a suspender-type deal, worn under his BC because he couldn't get all of his weight on a belt).
I could go into the gorey details, but let's just say this: Clearly, overweighting killed this guy. We could speculate that if he'd been more aware, if he'd been diving with a buddy (they were "same ocean" buddies), if he'd had a little larger tank, if he'd had a Spare Air... I don't care. Plainly, all of those things contributed to this guy's death, but none so obvious as the fact that this guy was wearing 108 pounds of lead. He simply couldn't get rid of it all in time to surface.
Would the solution be to make sure it's ditchable? No... The solution would be to be correctly weighted in the first place.
Why was this guy so radically overweighted? Well... He was a megalodon shark tooth hunter, and he believed that if he was radically overweighted, he could dig better, and thus find more teeth. Was that true? Nope... He only found as many teeth as the rest of us did... And we were all correctly weighted. Two months before his death, he and I got into an argument about his weighting techniques, and he chose not to be on the team any more. Darkly amusing that they asked me to recover his body.
I'm not saying that everyone's gonna die if they're 5 pounds overweighted... I'm just saying that a diver should be correctly weighted - and that if he is, he won't need to ditch at depth, which is a really bad idea anyway (how would you stop the uncontrolled ascent from 20' on up? It works in reverse, too... If you can't swim 20 pounds up, then you certainly aren't going to be able to swim it down...)
It is NOT what every agency teaches. Even GUE teaches you either to have redundant buoyancy, or ditchable weight, with the former vastly preferred.
I've never seen any agency that does not teach correct weighting techniques and who doesn't drive home to NOT ditch weight at depth.
GUE teaches a "balanced rig," which philosophically stems from the holistic dive style. I have never heard in one of my GUE classes that it would be a good idea to ditch weight at depth.
