Questions re: Weight of Tanks etc.

[sytech]

My diving has always been to tropical waters where I need only a diveskin or MAYBE a 2 mm shorty. The amount of added weight I need is about 14 lbs. (7 lbs. in each weight pocket on my BCD).

I will be giving colder waters a try along the coast here in New Jersey or at Dutch Springs Quarry on Pennsylvania.

I will most like buy a 7mm full wetsuit and a separate 2 or 3 mm vest with hood. That will give me about 10 mm of neoprene insulation and will obviously cause me to need more ballast than the 14 lbs. I mentioned above. The question is how much more?

I am considering purchasing a 80 size tank but wanted to know what the weight differential is between the aluminum tanks and the steel tanks?

Also, could that difference in weight be considered as extra ballast to offset the buoyancy of my 10 mm neoprene insulation?

Finally, as I remember tanks for Nitrox are made of a heavier gauge metal because the extra oxygen in the Nitrox mixture increases the potential for an explosion. How much heavier are those tanks and can they be also used for regular air (I assume they can, but Nitrox should not be put in regular compressed air tanks).


Any comments and suggestions will be appreciated.

Thanks,

Sy

 

[SparticleBrane]

Let's discuss a few other things, first.
Have you done a proper weight check with your gear in tropical waters? I can't imagine anyone requiring 14 pounds :11: :11: in tropical waters, especially in only a diveskin or a 2mm shorty. It sounds as if you're quite overweighted.
If you get a chance, drain a tank down to ~500 psi and see how much weight you need to remain neutral at your last stop (probably 15ft) with no air in your BC. I believe you'll be pleasantly surprised that it probably will be much less than 14 pounds.
As an example, last time I was diving in tropical waters off of Key Largo, I was in a 3mm full wetsuit using an Al80 tank and a ss backplate/wing setup. I used no additional weight.
In colder water with a 6.5mm two-piece wetsuit, an Al80 and the same backplate/wing setup, I use ~12lbs of weight. You can perform the same weight check as described above in cold water if necessary.

Go here for a page on tank specs. Al80s are 4.4lbs positive when empty and 1.4lbs negative when full. A Worthington X7-80 steel tank is -9lbs full and -3lbs empty. You would be able to drop ~7 pounds from your weight belt.

Finally, as I remember tanks for Nitrox are made of a heavier gauge metal because the extra oxygen in the Nitrox mixture increases the potential for an explosion. How much heavier are those tanks and can they be also used for regular air (I assume they can, but Nitrox should not be put in regular compressed air tanks).

Incorrect. Tanks used for nitrox and for air are exactly the same in terms of their construction, wall thickness, alloys, etc. The only possible difference is how they might be cleaned for usage of oxygen. Who told you that nitrox tanks were constructed differently???

As long as the nitrox isn't prepared using partial pressure blending, nothing special is required, although I'd use viton o-rings and oxygen-compatible lubricant on the valve thread. You can use nitrox and air in the same tank, back and forth as long as you want, as long as the ntirox isn't made by partial pressure blending.
If the nitrox is prepared using partial pressure blending (meaning that pure O2 is put into the tank and then topped off) then the tanks must be O2 cleaned. Tanks that are O2 clean must use O2 compatible air to stay free of hydrocarbons.

As I said earlier, there are no differences in the construction of "nitrox tanks" or "air tanks".

 

[captain]

I would agree with SparticleBrane you seem to be way overweighted. I use 15 pounds with a full 7 mil suit and only about 4 pounds with no wet suit or a 2 mil shorty. Get rid of all unneeded weight and your bouyancy control will become much easier.

 

[fisherdvm]

Here's a link for some tank info. It is nice to know how many pounds do you have to add to stay down with buoyancy check with a full tank.

http://www.njscuba.net/gear/eqpt_05_tanks.html

 

[pir8]

I dive Jersey and Dutch all the time. In my wet suit(7mm) I will carry 6lbs with my steel 120. I would think that you are overweighted.

 

[SparticleBrane]

Here's a link for some tank info. It is nice to know how many pounds do you have to add to stay down with buoyancy check with a full tank.

http://www.njscuba.net/gear/eqpt_05_tanks.html

That site is full of bunk and complete misinformation. I would completely ignore that link.

 

[roakey]

That site is full of bunk and complete misinformation. I would completely ignore that link.

I enjoyed the typical "I ain't got a clue" misinformation on DIR!

Roak

 

[spectrum]

My diving has always been to tropical waters where I need only a diveskin or MAYBE a 2 mm shorty. The amount of added weight I need is about 14 lbs. (7 lbs. in each weight pocket on my BCD).

I will be giving colder waters a try along the coast here in New Jersey or at Dutch Springs Quarry on Pennsylvania.

I will most like buy a 7mm full wetsuit and a separate 2 or 3 mm vest with hood. That will give me about 10 mm of neoprene insulation and will obviously cause me to need more ballast than the 14 lbs. I mentioned above. The question is how much more?

I'm sure you know that this is a big wild card.
For me the 7mm Bare Arctic (7mm) and the 3mm hooded chicken vest require 20 pounds in the ocean. My only 2 mm shorty dives here at home is fresh water and for that with the same gear I need 3 pounds of positive buoyancy (foam blocks ion a soft weight belt), it was actually a no BC dive with only lung volume for buoyancy control. That's a 23 pound difference, 6 of which is attributable to the water change so it's a 17 pound NET change. YMMMV but at least this is a data point to work from. FWIW my cylinders are PST E7-80's.

I am considering purchasing a 80 size tank but wanted to know what the weight differential is between the aluminum tanks and the steel tanks?

This is significant for someone making your transition and it sounds like you are already on to the concept. see this link: http://home.gwi.net/~spectrum/scuba_al80.html
While I cite my currently unavailable PST E7-80's the Worthington X series cylinders will work out just as well, in fact a tad better in some respects. I will probably update the page to reflect the available product soon.

Also, could that difference in weight be considered as extra ballast to offset the buoyancy of my 10 mm neoprene insulation?

Actually it's the difference in buoyancy but in the end, yes you get to leave some weight in the car. See the referenced page for actual calculations.

Finally, as I remember tanks for Nitrox are made of a heavier gauge metal because the extra oxygen in the Nitrox mixture increases the potential for an explosion. How much heavier are those tanks and can they be also used for regular air (I assume they can, but Nitrox should not be put in regular compressed air tanks).

There are no differences in the actual cylinders for nitrox. The cylinders need to be 02 clean to control the explosion risk and you need to be careful that any air introduced is suitable for O2 service. There are subtleties to all of this that will be covered in your nitrox course.

Any comments and suggestions will be appreciated.
Thanks,
Sy

Have fun and welcome to cold water diving!

Pete

 

[F106A]

My diving has always been to tropical waters where I need only a diveskin or MAYBE a 2 mm shorty. The amount of added weight I need is about 14 lbs. (7 lbs. in each weight pocket on my BCD).
I will be giving colder waters a try along the coast here in New Jersey or at Dutch Springs Quarry on Pennsylvania.
I will most like buy a 7mm full wetsuit and a separate 2 or 3 mm vest with hood. That will give me about 10 mm of neoprene insulation and will obviously cause me to need more ballast than the 14 lbs. I mentioned above. The question is how much more?
I am considering purchasing a 80 size tank but wanted to know what the weight differential is between the aluminum tanks and the steel tanks?
Also, could that difference in weight be considered as extra ballast to offset the buoyancy of my 10 mm neoprene insulation?
Finally, as I remember tanks for Nitrox are made of a heavier gauge metal because the extra oxygen in the Nitrox mixture increases the potential for an explosion. How much heavier are those tanks and can they be also used for regular air (I assume they can, but Nitrox should not be put in regular compressed air tanks).
Any comments and suggestions will be appreciated.
Thanks,
Sy

Welcome to NJ diving. It’s different but fantastic! Maybe you can use the following as a guide of sorts: I live a couple of miles from the ocean in NJ and have been diving here on my boats and shop boats since ‘95. In the tropics using a 2MM shorty with an AL80 I use 8-14# depending on how the diet is going. Having said that: Diving a 7MM drysuit, PST E7-100 and AL19 pony, I use ~30# total; 26 on the belt and ~4# on the ankles. With a 7MM farmer john/jacket, AL100 and AL19 pony I use ~26# total. — I really like those PST 100's; they allow me to shave about 6# off the weight belt. For NJ you might want to consider the following: 100's rather than 80's. Most of your diving will probably be in the 70-90' range. Or deeper. Or much deeper. Very few dives are in the 60-70‘ range. Use that www.njscuba.net link from another replier to check out tank specs, empty/full weights, lengths, diameters, etc. It’s a great site and has lots of useful info for getting a feel for NJ diving. Also, almost all boats require a pony unless diving doubles. (A very few shops don’t require them if the dive is less than ~60-80'). And, a 7MM farmer john/jacket combo for that 14MM around your trunk. It gets chilly on the bottom around here. The warmest I encountered last summer was ~57 at 80-110'. And two tanks are better than one since the boats typically do two dives per trip. IF, after reading my praises of steel tanks, you think you might be interested in a couple of used AL100's I have two I’d be willing to part with. HTH

 

[SparticleBrane]

^ You sound really overweighted too. 30 pounds?!