Aotus
Contributor
And what do need a lower dump for?
The BIG problem is that the butt-plates over the rear of the wing on the SMS rigs end up pushing the air out of the bottom of the wing when heavy steel tanks are attached. You can adjust your tanks and weights to accommodate this, but if you then switch to AL tanks on your waist, it's like you suddenly have a whole extra 6" of wing at the bottom, and unlike the top of the BC, there is no bungee to compress the area and keep the gas even. Using my SMS75, it meant I was suddenly VERY butt-light and it was a real problem getting enough weight low enough to correct for it. Also, with the inflator and dump reversed, the gas had to move all the way from by butt to my shoulder to dump, and that meant going WAY out of trim to dump...
I'm not making this stuff up Benno. Good for you that you haven't experienced these issues, but that does not invalidate the experience of others. Using AL80s and a wetsuit, I was not able to dump my SMS75 this summer without leaving trim, or reaching behind my back and squeezing the low part of the wing to move air towards the top dump near my shoulder. That is a fact. Using steels (with or without a drysuit) not an issue, using AL80s is a problem.You can dump your wing without a lower dump while staying in trim, that's a FACT!
I don't know what you have against bottom dump valves, but I think your definition of side dump(on the razor) fits in our definition of bottom dump... that is, it is not at the top like on the SMS100(and SMS75), which is, if you recall, the topic of this thread. Also, it's weird that you're so critical of the stealth, another bottom-dump wing that is, you cannot deny, designed and used by "REAL" sm cave divers, one prolific SM cave explorer specifically, Patrick Widmann.Razor has the dumps on the side and no lower dump and it's also designed by real SM divers. Cave divers.
Back to the point of this thread...We already agree that the SMS BCs are no good for AL80s. My whole position in this thread is that the SMS100 is not ideal because it is limited to functioning well with steels, and not because there is anything special about steels, but because the way they are mounted functionally changes the shape of the wing so that the gas is not allowed to sit in the lumbar region. I argued that the problem with using AL80s is that the pressure on the low part of the wing when using steels(via door handles) is gone, the whole wing is suddenly functional again, and the air is stuck in the low position. Thus, a low dump may resolve that problem. As Andy pointed out, BP/W setups do well with a low dump. Because the triangular shape in the SMS75 wing, and in effect also the SMS100 (from bungees over the top of the wing, top also constricted by CA or other mods), the gas will be over the low back. This is by design for ideal trim, which, you know all about. Tell me then, what is the point of having the dump valve so far from where the gas is intentionally kept? I'll grant you that the ease of tugging at the dump valve when on the chest is comforting, but if so many "real sm" divers with stealths and razors can reach behind them, is there a reason we cannot?
If others CAN use a bottom dump, what is the benefit of top dumps for us? What is the benefit of the SMS BC? I would argue that the most significant benefit of the SMS100 and SMS75 is not for specialization for use with steels - there are "real SM" rigs with bottom dump valves that work fine for steels. Rather, (1)the top-dump of the SMS BCs make it a little easier to reach a dump valve for (hyperactive?) buoyancy tweaking. Also, (2)top-dumps allow for dumping when the diver is head-up, which is not a position that we cave divers are supposed to take, but in FL caves it's not unusual to see a slightly knee-low diver. Together, one could argue, these "benefits" enable and even promote poor buoyancy control and trim, in addition to reducing the efficacy(or at least efficiency) in dumping gas.
The next question for the new SM diver considering the SMS100 or SMS75 is, where should the inflator be? Can I just leave it on the top of the SMS100? The answer depends on your application. In cave diving, we don't want something like the elbow of an inflator hose sticking out behind our head - it isn't protected by the manifold of a double set when you dive sm. So a bottom-mounted inflator still makes sense. It's my opinion that more and more wings are becoming razor-esque or stealth-esque for a reason. This model - bottom dump, bottom inflator, wing volume limited to the lumbar area - WORKS! So, congratulations big innovators Razor and XDEEP, you worked it out, and now you're going to be copied forever with tiny tweaks by everyone else claiming that they've reinvented SM diving.
That's just my position, not gospel. YMMV.
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