Audimaniac(Offline)

Hi all,
I am very new to DIR and have my fundies booked with Brian in August. I have already got my kit and twins set up in acceptable DIR config and am happily getting used to it but I am constantly having arguments with one of my dive buddies about the correct set up for twins. Basically, without opening up a huge can of worms (hence posting here and not on YD) I need a definitive reason why we use twins fixed “upright” instead of inverted.

The problem is my buddy is Ex Royal Marine and is a very accomplished recreational diver. He is also wanting to go down the twin route but insists that he will use his twins inverted as that is the correct way. He cites the Royal Navy divers as an example and also make a very good case for bio-mechanics (in that operating valves on inverts is far easier and “natural” for our limbs than with uprights). He states that entanglement issues are the same with both and that hoses will route over the shoulder in any case.

I can’t seem to find a satisfactory and definitive answer to his question as to why DIR divers set them up they way we do and not inverted. I just need that convincing reason to give him.....Can anyone help? As with most DIR questions I expect the answer to be blatantly obvious once I know it and I promise to go stand in a corner with the Dunce hat on….!

Thanks

Fiona(Offline)

Coward

I am sure someone better qualified than me will be along shortly to answer your question but I am guessing one of the reasons is standardization of equipment - but I am probably wrong (I frequently am)

I dived inverts for about 3 years up to 18 months or so ago (Sept 2006) and looking back the only reason I did so was because I thought I couldn't shut the valves down and there was so much on YD about it when I joined, after seeing someones set on a YD I decided it was the best route for me.

I look back now having had some "proper" training and encouragement from here that it really wasn't the issue. Also I see photos of my kit when it was inverted with hoses everywhere - it just looked like a bag a cr**

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iainmsmith(Offline)

1) You can use "upright" cylinders with any size of tank. If you invert twin 18s, the diver will be massively top-heavy.

2) Doing an air-sharing exit through a restriction, you may be one behind the other. The recipient will be in front. (If the donor gets snagged/held up on something, the recipient is not going to out-swim his/her gas source. Put the recipient behind and if he/she gets snagged and the donor doesn't realise instantly, there is a high chance that the reg will get pulled out of the snagged diver's mouth and be out of his reach. If it's a tight restriction, the donor may not be able to turn round to get the reg back to the recipient. So the recipient goes in front). This therefore requires that the donated hose has sufficient length to run from the pillar valve along the full length of the recipient diver...which works out about 7' long.

This great length of hose could be stowed bungeed against the tank...which some will recommend and which works fine until it has to be deployed and ties itself in knots (seen it happen when an advocate of this method was trying to demonstrate its superiority). At which point you can't donate the full length and you now have a lovely set of loops sticking out from the side of your tanks...just right to get snagged. So we "wrap" the long hose. This takes up a good couple of feet running down to the waist and under the light/waist belt before it comes back up across the divers chest.

If you now invert cylinders you a) need an extra 2' of hose so that it can get from the tanks to the OOG diver and b) have lost 2' of "storage space". You've now got 9' of hose starting at your right hip...how do you store it?

3) If you get stuff tangled around your valves, it's easy for your buddy to see if they're behind your head. If the valves are behind your butt, your legs are in the way. Not insurmountable, but more of a PITA.

RN Ship's Divers work in very different conditions. They are, in general, shallow, no restrictions, no overheads (other than the bottom of the ship). They are (I think) solo and I'm not sure whether they use contents gauges or whether they still plan their dives with the isolator closed, opening it when the first tank is exhausted (50% left), then closing it, then repeating (25% left), then coming up. AFAIK they also use the same size of tanks every time. It's a configuration that works well enough for that particular environment. It doesn't scale up or down to other types of diving, though.

Your friend is correct in that it's much easier to turn valves on typical inverts. However, by taking a little time to set up one's kit (and it may take a few dives to tweak it), almost everyone can get their upright tank valves in a place where it is sufficiently easy to get at them that the embuggerance level is minimal. And you get the advantages outlined above. And there are probably others that haven't immediately come to my mind.

HTH.

Iain

Michael-Fisch(Offline)

Valves on inverted tanks become unreachable as soon as you start carrying a tank light on the right hip and stage tanks on the left.

It seems to me that the solution (inverted tanks) is worse than the original problem. I'd try solving the original problem first:

Put more air in the wing and dump the air out of the drysuit before reaching for the valves.

Move the bands lower on the tanks to raise the height of the valves.

Loosen the shoulder straps on the backplate, they should NOT BE TIGHT.

Streach and exercise your muscles until you have the needed range of motion.

If you can get to the valve knobs but they are hard to turn, replace the knobs with Sherwood rubber knobs, and have somebody who knows what he is doing, clean and lube the valves - I can roll my valves open and closed easily using only the palm of my hand.

Michael

tim(Offline)

I continue to be intrigued by this one. Reaching valves on an upright set appears to me to involve only a small flex of the elbow - the same minimal and to my mind very natural movement as required to, for example, touch the back of your neck with your finger. Reaching where I think the valves would be on an inverted set appears to me to involve a much larger movement with either a full arm sweep or a more complex shoulder rotation with an elbow flex and then extend. That movement is OK for a routine procedure like checking backgas SPG but seems a bit too complex when a much simpler urgent 'flex elbow to manipulate valve' option is available.

When the diver is standing upright with their arms at their sides, the inverted tank valves would seem to the simpler movement, but in the prone diving position with arms forward I can't think of a simpler movement to reach the valves than the elbow flex. I wonder if people arguing inverts as more natural start their thinking from 'standing upright' as opposed to 'lying prone' ? Is this another case of people working out 'easier' methods whilst forgetting that they are carried out underwater rather than standing on land?

Tim

TDave(Offline)

Another one that I didn't originally think of / hear anyway but have seen it happen in practise is the little fact of actually being able to hear if you have air pissing out of your first stages / valves.

Those who've tried simulating with an air gun valve failures with the tanks upright will no doubt testify that it's pretty damn obvious when air is rushing around your ears. No doubt those who've suffered it for real would attest to the same thing.

However, I've seen a good few people now, diving inverts, who in the same simulation simply can't hear the air pissing out, as it's right down at the bottom of their back - a long way from their ears!
It may well be different in a 'real' situation, but after seeing this a few times it also seems to make a pretty solid argument!


As others have said though, to me, the biggest factor is the long hose. Just as Iain pointed out - to be most effective, the donatable hose needs to be about 7' long. Sticking these on inverts (without bungee.. ;-) ) gives you a good couple of foot-worth of hose flapping about with nowhere to go (presuming you were trying to hog loop it).

Besides that... it just doesn't look right... :-D

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LCF(Offline)

From my experience with the Fusion dry suit, I have come to believe that the vast majority of difficulties people have with reaching their valves are related to being restricted by their exposure protection. I struggled mightily with valve drills until I dove doubles in a wet suit in Mexico last October, where it was simply no issue. I have had the same experience with a Fusion. And I have had shoulder surgery on the right side.

Anyway, if that's the case, the only real argument in FAVOR of inverted tanks evaporates.

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Retardboy(Offline)

And of course you have the simple argument that it's just more practical to be able to put down your set without valves and regs in the way If reaching valves is his only argument...well, then he doesn't have any arguments Unless he has some injury of some sort of course.

Look at my bubbles!

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Rubis(Offline)

I have never tried doubles inverted, I would think that having the valves down, it would keep the weight below the waist, thus giving a seahorse trim instead of a nice flat trim.
Also reaching the valves should be more difficult, once you start piling up stages. The valves would also get easily damaged when going on a boat for example.

My husband and I have just switched from a typical doubles DIR set up to diving Kiss rebreathers. We have rigged our tanks valves up and we have definetely improved the trim and the accessability of the valves this way.

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Fiona(Offline)

Audimaniac look what you have started

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