Looking for triple manifold

[John C. Ratliff]

A few more thoughts:

For years, we in Pararesuce used twin 40s as our jump tanks, and they were sufficient for most of the rescue work we did. The above setup would be fairly complex, it I think that a double 40 setup would probably suffice for what this person has in mind.

Finally, the most streamlined configuration is a single 72, set up as a vintage system with only a single hose regulator (no SPG, no LP other hoses, just a single hose to the second stage) and a J-reserve valve. It is easy, cheap, and works extremely well. You would want an older-styled backpack with shoulder and waist straps only, and wear it lower than divers tend to do today. You need that shoulder strap loose so that the diver has freedom of motion with his/her arms, to reach above on the bottom and pull yourself along in heavy current.

SeaRat

 

[james croft]

I am familiar with much of that but if a victim is trapped by current then a diver may become trapped as well, especially with the increased drag of equipment. I often dive in rapid areas of rivers and understand the friction loss of currents at the bottom of rivers. What I refer to as swiftwater is water in which a diver may not swim against. Even water that may be swam against through much effort will soon exhaust a diver. Even worse is when divers are tethered in swiftwater. There may be certain areas in fast moving water that a diver may enter, such as eddies below rocks or deeper pools. Overall I would be hesitant to put a diver into any swiftwater based on the risk of losing another diver or more to effect the recovery of what unfortunately is usually a deceased person. I patrol white water areas by kayak and jet drive zodiacs and dive portions of the river where current is significant but not what I consider swiftwater. Our state dive team protocols do not allow a diver in water faster than 2 knots. The last swiftwater fatality I investigated held a kayaker underwater against strainers for over an hour. That was a person wearing a drysuit and a PFD. It would have been a death sentence to have attempted a rescue or recovery for anyone who would have made the attempt.

 

[Nemrod]

Thing is I suggest he obtain a double set up, independent or otherwise. I have a set of narrow C/C stainless bands for independent doubles--just got them mostly by accident. The problem with triples is that they will not fit to any commonly available back plate system. A modern back plate has a center channel that uses two bolts to mount the tank bands, the triple set middle tank would sit up on this center groove making it unstable and would require welded bolts to the center band--or something--not really sure what would work.

I show this image ONLY because it shows modern bands mounting to a modern back plate. See the problem there with a triple?

Now, you might be able to secure an older type plastic plate, mount the center tanks with cam bands and then cantilever the side tanks like John suggested or with custom triple bands. I suppose this could be done with a modern back plate with the center tank mounted with a STA and then the rest rigged as just described. Yeah, I suppose that might work. It might not be very stable.

Triple tanks were more prevelent in Europe but only enjoyed a brief popularity in the USA. I think most can see why,weight, width, suitable tanks etc. N

 

[duckbill]

Why triples, or even doubles for that matter?
If he is looking to be streamlined with 120 cf, he would be better off with one 120 cf tank.

Do the math:
1- 120 cf 7 1/4" tank = 41.3 in2 exposed to current (Assuming he is facing it. Side current is another story.)
1- 120 cf 8" tank = 50.2 in2

compared to:
3- 40 cf 5 1/4" tanks = 64.9 in2 NOT INCLUDING the area of the manifold bar.

What diameter 40 cf tanks is he considering?

I dive river currents. I know what they are about. Even without any current, doubles offer significantly more water resistance than a single (having equal diameters). I'm not so sure that lower to the back necessarily equates to being more "streamlined". The area and contour of the surfaces facing the current are what matter. One larger tank may be better than three smaller tanks.

Any other thoughts on this before the guy buys himself an expensive and potentially life-threatening dissappointment?

 

[Nemrod]

I was not exactly following the reasons either duckbill before we all got sucked into figuring out how to do it--I suppose because singles are boring?--Maybe?

I think your essentially right, a large single with a H valve or Y valve may be the ticket.

Doubles and triples are so cool and pro looking and make me think of SeaHunt monochrome seas but the fact is I prefer a single tank which underlies most of my protestations with the Men in Black.

N

 

[John C. Ratliff]

As I said above, a single tank is the most streamlined scuba available. We used a single 72 or Al 80 for years in heavy current without problems.

John

 

[duckbill]

I saw that John. Didn't mean to ignore you.

By the way, Jim, John calls himself "SeaRat", but he's quite the River Rat, too. Your customer can take his advice to the bank.

 

[D_B]

*off topic* Dang! that looks sweet, Nemrod

 

[John C. Ratliff]

I have dived the UDS-1 is current, and it handles very well. It is about like my twin 42's, but not as streamlined is a single 72. While it has more air, and is a very streamlined unit (once it is correctly balanced--if not balanced by about 6 pounds of weights in the top, it is very bad), it still will have a greater cross-sectional area presented to the water than a single 72 will. It will also weigh more. I really like the UDS-1 (a triple-tank system made by U.S. Divers Company in the late 1970s, with a cowling over the tanks), I would not recommend anyone pick it up as it is very difficult to deal with for maintenance and breakdown. It takes me about an hour to break down the system, and another one- to two-hours to put it back together correctly. Here are some of the threads on the Vintage Scuba Supply website where I have written about the UDS-1:

http://vintagescuba.proboards2.com/index.cgi?action=display&board=general&thread=1156958954&page=1

http://vintagescuba.proboards2.com/index.cgi?board=general&action=display&thread=1095723435&page=1

SeaRat

 

[John C. Ratliff]

Why triples, or even doubles for that matter?
If he is looking to be streamlined with 120 cf, he would be better off with one 120 cf tank.

Do the math:
1- 120 cf 7 1/4" tank = 41.3 in2 exposed to current (Assuming he is facing it. Side current is another story.)
1- 120 cf 8" tank = 50.2 in2

compared to:
3- 40 cf 5 1/4" tanks = 64.9 in2 NOT INCLUDING the area of the manifold bar.

What diameter 40 cf tanks is he considering?

I dive river currents. I know what they are about. Even without any current, doubles offer significantly more water resistance than a single (having equal diameters). I'm not so sure that lower to the back necessarily equates to being more "streamlined". The area and contour of the surfaces facing the current are what matter. One larger tank may be better than three smaller tanks.

Any other thoughts on this before the guy buys himself an expensive and potentially life-threatening dissappointment?

Duckbill,

I like your figures. If you look at the calculation, the double 40s would be 43.3 square inches, while the single 120 is 41.3 square inches, which is a close equivalent. But if you look at these in profile, sideways, the twin 45s would have a significantly reduced surface area presented to the cross-current. In this manner, the steel 120 (length of about 30 inches, diameter of 8 inches) presents about 240 square inches to the water, whereas the twin 45s would present 127 square inches to the water (not allowing for the rounded shapes, just the profile). So in this respect, the twin 45 would be better in the current from a total handling point of view. This would indicate that the twin 45s would overall out-perform the single 120. A single 72, having a somewhat lower profile (6.72 x 25 inches) is between these figures at 168 square inches in profile.

Why is the profile important? Well, coming around large boulders (such as I see in the Clackamas River) will give some interesting cross currents, especially in the early spring when it is fairly high (not flood, but fairly high). There can be a great amount of turbulance, and that can hit from unexpected directions. In these circumstances, the lower the profile, the better. I'm using the OMS website for the tank dimensions ('don't have another source that's easily accessible, and I have never dealt with OMS for any equipment):

http://www.omsdive.com/cyl_spec.html

My comment about having the tanks lower on the back is for two reasons. First, the lower down it is, the more it is likely to fit into the eddie created by the diver's head, and not give so much profile to the water. Also, many people have a noticable rounding of the upper back and shoulders. Lowering the tank(s) puts the cylinder below this rounding, and therefore decreases the cross-sectional area presented to the water (as the back itself already is presented to the water here, and I realize that I may simply be talking about myself, and how my body looks in the water).

The second part concerning the idea of dropping the tank has to do with lengthening the shoulder straps. This gives the arms much more freedom of motion forward. Swimming with the arms forward is more streamlined than trailing the arms, and also provides for getting into the eddies on the bottom and using the hands to pull one's self along.

Overall, I have had very good success diving heavy currents with either singles or doubles. Though it is possible, I would recommend against setting up triples for this purpose, even though I do with my UDS-1 (see above).

SeaRat