100cf tanks

[Greg Doyle]

I'm at about 10 dives so far and I've still got my training wheels on. I find I blow through air much quicker than fellow divers. I had a shop suggest I might try going to 100CF tanks until I get my breathing under control.
My question, I assume this changes the weight I'll need, but not by much as I enter the water, more so as I use the air. Won't a larger tank make me more buoyant toward the end of a dive than an 80CF tank?

any other down side to using a 100cf tank?

Thanks,
G

 

[MaxBottomtime]

A Catalina 80 aluminum tank has a buoyancy of six pounds empty with a -1.8 pounds when it's full. A steel 100 is -one pound empty and -8.5 pounds full. You would probably be able to remove seven pounds from your weight, however as a new diver you will find that as you get more comfortable in the water and stop moving your arms you will need less weight anyway. Your air consumption will also decrease, making your dives longer.

The only downsides to using a steel tank are the cost and weight out of the water.

 

[geomatt21]

The real answer to the weight adjustment you will need lies in the metal the tank is made up of.

If we assume you're using an aluminum 80 that is ~4lbs positive and the shop is suggesting using a steel 100 that is ~1 lb negative, then you could safely take 5 lbs off of your dive set-up.

Aluminum 80 tanks vary in their buoyancy at 500psi, they can be neutral, or up to 5-6 lbs positive depending on the manufacturer! Between the two Aluminum 100s out there - Catalina's are 0.4 lbs negative and Luxfer's are 3.1lbs positive at 500psi I am guessing the shop was suggesting STEEL 100s rated to ~3500psi and for simplicity sake let's say they are between neutral and 2lbs negative at the end of a dive depending on the manufacturer.

The difference between the weight of 80cf and 100cf of air is negligible - being an additional 1.6 lbs of air in a 100cf tank. To be clear, the weight of gas is not important (to recreational divers) since we only care about the tanks' buoyancy when at 500psi.

 

[ColoDale]

I am more bouyant with AL 100 CF tanks at the end of the dive especially on the surface. I do safety stops betwen 15-20 feet. I have a back inflate BCD so it tends to put me more face forward on the surface. I use weight in the pockets on the tank bands to help offset it. I also use a weight belt not integrated. You did not say if the 100's are steel or aluminum. Other than being a bit heavier when full over 80's, I don't see downsides to using them.
I use 100's as I am 6'7" ~260 lbs so I end up at the same point as those with 80's.

 

[Yancey M]

@Greg Doyle check this link out:

http://www.indianvalleyscuba.com/services page/Tank Inspection/information/CYLINDER SPECIFICATIONS.pdf

Its a chart that list aluminum and steel tanks, it gives you the size and buoyancy of most common tanks on the market today.

Depending on weather you're talking about aluminum 100s or steel 100s there can be a big difference. Even different brands or models change the buoyancy characteristics +/- a few pounds.

 

[decompression]

Hey Greg, if I may......instead of spending money on tanks, I would suggest investing that money in yourself and take an extreme scuba makeover class. I can almost guarantee you'll increase your comfort in the water, lose a considerable amount of lead off your belt and perfect your trim and buoyancy. All of those things will transfer into a considerable reduction in air consumption. I know it sounds like a sales pitch but it works and it work very well. There's a great shop in Seattle called Frogkick diving.

http://www.frogkickdiving.com/

Extreme Scuba Makeover · UTD Scuba Diving

 

[geomatt21]

Hey Greg, if I may......instead of spending money on tanks, I would suggest investing that money in yourself and take an extreme scuba makeover class. I can almost guarantee you'll increase your comfort in the water, lose a considerable amount of lead off your belt and perfect your trim and buoyancy. All of those things will transfer into a considerable reduction in air consumption.

This is so very true. I recently took a similar GUE class after 5 years and 400 dives and it increased my comfort in the water and decreased my breathing rate/air consumption. If you have the money to get the steel 100 I'd say to go for it. Regardless of any change in air consumption, you will have longer dives and 5 or more lbs less weight on your belt/integrated pockets.

 

[boat sju]

If you do decide to get a tank I suggest you take a close look at HP steel 100's. Their buoyancy characteristics, actual weight, and size are great for cold water diving.

 

[Greg Doyle]

Thanks for the replies folks. I'll find out tomorrow if the tank is Al or steel.
It's a wreck dive to just over 100' and the last time I did that, I went through air way too quickly. I'm also going to take the Eanx test on Sunday.

This is a business trip in FL and starting next week I'll be back home and jumping in Puget Sound for Dry Suit training with my LDS. I'll do the class with 80s.
I'm still a ways out from purchasing tanks.
Decompression, are you in the Seattle area? I see the 206 area code.

In the mean time, as little diving as I've had with the dry suit so far, it's a completely different ways of diving from here in FL. I'd be open to a GUE class while here in FL. Perhaps the next trip down.
Thanks,
I'll look into it.

 

[Steve_C]

I have dove a variety of tanks but my go tos are steel 100s. I am 5'7", used to be 5'8", and with Al80s and other long tanks they tend to hit me in the butt (and they are not hung low). HP 100s fit me really well.

Filled correctly a 100 is 100. Filled correctly an 80 is not an 80. It is a bit less than that.