Wing lift recomendations for BIG tanks

[nielsent]

Okay, so I am slowly starting down the path of Tech diving and have a question regarding recommendations in configuration.

I recently purchased two Pressed Steel Low Pressure (2400psi) 120cuft cylinders (19L ~160 BAR steel tanks for all you metric divers), which a friend of mine could no longer dive due to size limitations. Currently I dive them as single tanks with a halcyon BP and eclipse #40 wing and have keyed in my weight almost perfectly while wearing a BARE CD4 compressed neoprene drysuit and undergarments. I am a biggish guy weighing in at 220lbs and 6'2" tall, and I find that these tanks are an excellent fit for my kit and really enjoy them, even though I get a lot of people gawking at their size.

Now because I am near broke, and like the tanks. When I start into tech diving I would like to continue to use these tanks, but in a doubles configuration, and most likely with the same exposure protection (as I won't be taking these monsters anywhere tropical unless someone else is paying the baggage charges ). These tanks were originally setup as doubles, and i have the manifold and bands to put them back that way. However, because of the massive size of the PST LP120: 29.5" long and 8" diameter, ~61lbs on dry land when full, and according to specs -10.7lbs bouyant full and -1.7lbs empty. The major issue I am concerned with is choosing the proper wing to compliment these tanks. According to some rough calculations, I would need a minimum of 56lbs of positive buoyancy for the setup, but from experience with these tanks, I don't know if that would be enough to keep them afloat at the surface if i had to remove the harness in water. Also, I have noticed that most wings on the market are "maximum" rated for 17L tanks, and not 19L tanks, and as a result, I worry about that too.

Now that I have given you all the background, as much of the specifics that I can think of, and the problems, here are the questions.

1) What wing (both capacity and brand if there is a preference) would you recommend for a system like this?

2) Is the calculated bouyancy I came up with reasonable, or is my paranoia justified and would a more bouyant wing be necessary for this setup?

Thanks for your time and recommendations in advance.

 

[LeadTurn_SD]

Hi nielsent,

There are a couple of figures you need to determine before you can estimate how much lift you need for a wing.

1.) The buoyancy of your exposure suit. Your wing needs to able to compensate for this buoyancy if it is lost at depth.

2.) The buoyancy of your rig without you in it. Your wing needs to be able to float your rig on the surface if you need to remove it for any reason.

With the info you've provided, you can make a ballpark guess at the lift needed to keep your rig afloat on the surface at the start of a dive (when it is heaviest due to full tanks). If each of your tanks is -10.7 lbs full (including the valve?) then I'd use 22 lbs as the total tank weight. Then you need to add the weight of the backplate (about 5 or 6 lbs average for a steel backplate) the weight of the tank bands (5 lbs?), the weight of the manifold (5 lbs?) the weight of two regulator sets (3 lbs each, 6 lbs total?). 22 + 6 + 5 + 5 + 6 = 44 lbs.

So if all the guesses I've made are in the ballpark, something like the Deep Sea Supply 50 lb doubles wing might work:

https://www.deepseasupply.com/index.php?product=1330

The estimate above is a VERY gross estimate of the minimum lift to float your rig (you still need to calculate the buoyancy of your exposure suit). If you can get more accurate figures for the components that make up your rig, you'll get a more accurate minimum lift figure.

Then you really need to measure the surface buoyancy of your exposure suit to determine the amount of lift needed to compensate for lost buoyancy at depth.

A great resourse on this board is Tobin at Deep Sea Supply. He does these kind of calculations every day, and can walk you through it, and makes terrific dive equipment.

Good luck, and best wishes.

 

[elan]

If im not mistaken if you are properly weighted the minimum lift is calculated as the buoyancy of your suit + the weight of the gas. So if you have a suit that needs 20 lb to sink with your tanks you will need approx 9x2 + 20lb - 38 lb. Add some safety margin say 20-30% you get to 50lb.

All the ballast like regs , bands BP go against the buoyancy of the suit, and the wing has to support if the rig is floating on the surface of your suit is completely flooded. If you are overweight for some reason which is not good you add that weight to your calculation.

So check the buoyancy of your dry suit first - that would be the initial point. Find some shallow area and play with lead and see how much you need. Then go from there. Though your tanks might look big they are not different from say HP100 buoyancy wise.

Tobin will be definitely more helpful with this question.


PS. And, man, you better be 220lb of pure muscles and have a titanium back and knees to carry those things. 61lb each will be close to 140lb dry weight. My rig is 100lb and I cannot say I enjoy hauling it around. Unless you have that titanium joints or have a portable lifting device I would think twice before doubling them up.

 

[LeadTurn_SD]

If im not mistaken if you are properly weighted the minimum lift is calculated as the buoyancy of your suit + the weight of the gas....

All the ballast like regs , bands BP go against the buoyancy of the suit, and the wing has to support if the rig is floating on the surface of your suit is completely flooded. If you are overweight for some reason which is not good you add that weight to your calculation.

So check the buoyancy of your dry suit first - that would be the initial point. Find some shallow area and play with lead and see how much you need. Then go from there. Though your tanks might look big they are not different from say HP100 buoyancy wise.

Tobin will be definitely more helpful with this question...

Hi elan,

In general I think you are right: I think for cold water diving, using single tanks, the buoyancy of the exposure suit is often the deciding factor when calculating minimum lift for the wing. And depending on the buoyancy of the suit he is currently wearing, the suit may still be the deciding factor.

But what I'd worry about here is that with heavy steel doubles, a steel backplate, bands, and two sets of regs you do need to closely look at the buoyancy of the entire rig as well, to make sure you have enough lift to float it without the diver in it (so it does not turn into an expensive anchor if you need to remove it for any reason on the surface ).

Tobin is for sure "the man" when it comes to this stuff. Give him a call.

Best wishes.

 

[elan]

Hi elan,

In general I think you are right: I think for cold water diving, using single tanks, the buoyancy of the exposure suit is often the deciding factor when calculating minimum lift for the wing. And depending on the buoyancy of the suit he is currently wearing, the suit may still be the deciding factor.

But what I'd worry about here is that with heavy steel doubles, a steel backplate, bands, and two sets of regs you do need to closely look at the buoyancy of the entire rig as well, to make sure you have enough lift to float it without the diver in it (so it does not turn into an expensive anchor if you need to remove it for any reason on the surface ).

Tobin is for sure "the man" when it comes to this stuff. Give him a call.

Best wishes.

Yes for sure that case only applies when the weight of all necessary equipment is less then or equal to the buoyancy of the suit. It turns out to be the case most of the time here in our waters as the buoyancy of our suits with undergarments are most of the time close to 20 lbs so it is very difficult to overweight yourself with just the rig

When I dive single tank I add 14 lbs of lead and that's with an SS plate
but yeah if you generally have less buoyant suits you better have the calcs done with all ballast in mind just for the sake to make sure you are not much overweight in the first place and see you one needs to switch to floaty Al80 .

 

[scubafanatic]

Boy, I hope you're ready to handle those big boys on a rough shore entry/exit or be able to climb back into the boat in a high sea state, not fun!

 

[cool_hardware52]

Okay, so I am slowly starting down the path of Tech diving and have a question regarding recommendations in configuration.

I recently purchased two Pressed Steel Low Pressure (2400psi) 120cuft cylinders (19L ~160 BAR steel tanks for all you metric divers), which a friend of mine could no longer dive due to size limitations. Currently I dive them as single tanks with a halcyon BP and eclipse #40 wing and have keyed in my weight almost perfectly while wearing a BARE CD4 compressed neoprene drysuit and undergarments. I am a biggish guy weighing in at 220lbs and 6'2" tall, and I find that these tanks are an excellent fit for my kit and really enjoy them, even though I get a lot of people gawking at their size.

Now because I am near broke, and like the tanks. When I start into tech diving I would like to continue to use these tanks, but in a doubles configuration, and most likely with the same exposure protection (as I won't be taking these monsters anywhere tropical unless someone else is paying the baggage charges ). These tanks were originally setup as doubles, and i have the manifold and bands to put them back that way. However, because of the massive size of the PST LP120: 29.5" long and 8" diameter, ~61lbs on dry land when full, and according to specs -10.7lbs bouyant full and -1.7lbs empty. The major issue I am concerned with is choosing the proper wing to compliment these tanks. According to some rough calculations, I would need a minimum of 56lbs of positive buoyancy for the setup, but from experience with these tanks, I don't know if that would be enough to keep them afloat at the surface if i had to remove the harness in water. Also, I have noticed that most wings on the market are "maximum" rated for 17L tanks, and not 19L tanks, and as a result, I worry about that too.

A few basic points:

Dry land weights for anything have no bearing on required wing capacity. Buoyancy maters, mass does not.

Rating wings based on cylinder size is not very useful.

Exposure suit buoyancy is a major player in wing size calcs.

Without going into the detail behind the method the "back of the napkin" requirements for doubles is:

The weight of your backgas + the buoyancy of your drysuit + 2~3 lbs = minimum required wing capacity.

2 X 120's will hold about 20 lbs of air or nitrox.

If you suit is 28 lbs or less buoyant with minimum gas in it a ~50 lbs wing is about right.

If your suit is more than 28 lbs positive you likely need a wing ~55-60 lbs.

Very few undergarments + shell drysuit will be more than about 35 lbs positive.

You should test your suit before selecting a wing.

Tobin