How much extra time underwater do you get by buying 130 cu ft cylinder vs standard 80 cu ft? Last time I used 80 cu ft during my open water course in tropical waters, I used all of my air in less than 25 mins? Soon I'll be diving in the cool waters of lake superior.
I can't really tell you how much more time you'll get other than to suggest you do the math. A 130 cu Ft tank has 62% more air than an 80 cu ft tank so you should be able to get 62% more time given all other circumstances being the same. Comparing air utilization in tropical waters to cold water is more difficult.
No one will be able to provide an accurate answer to your question. Deeper depths and cooler water temperatures both increase the amount of air you suck in during a dive. If you suck an 80cf dry in 25 minutes in the warm waters of the Caribbean, you definitely need the larger tank in Superior. The 130 will give you a much needed advantage in the cooler waters of Lake Superior. I dive/spearfish off coastal NC. I have a 100cf Worthington and a 120cf Worthington. At 70' I get 55+ minutes on my 120. About 10 minutes less on my 100. I am going to purchase another 120cf.
I can say I see about a 10-15% increase in time. If you are going through air that fast, you need to work more on your breathing and buoyancy more than finding a tank that gives you more time. It will help, but it will not give you a 1 hour dive.
However, this is a GREAT short tank and I love it.
I usually get at least one hour of dive time. Plus a carry 10 lbs less weight.
Theoretically 63% more air. However, this tank is not technically 63% bigger. It is both a bigger tank and also rated at a higher pressure (3442 PSI). You definitely get more air, but you need to specifically ask for the tank to be filled to it's rated pressure. Also, this steel tank gets very hot if it is filled quickly. So, if it is filled to it's rated pressure and gets hot, when it cools the pressure will drop and your tank is not really full. I own this tank and you'll certainly get the benefit of more air, but it is a heavy tank.
It can vary by a lot of different conditions but you can expect at least around ten to fifteen minutes on average.
I can only vouch for the quality of these tanks. They are fine. I use mine for air gun filling. I also later bought a carbon fiber tank. They are expensive but very light and hold up to 4500 psi.
In simple terms a 130 Cu.Ft. tank has 62.5% more gas than a 80 Cu.Ft. tank so would give you that same percentage more bottom time. However most new divers find that experience will give them more bottom time without going to a bigger tank. It might also be beneficial to take an Advanced class before diving in the more challenging environment of Lake Superior.
Air consumption decreases with experience. 25 minutes of bottom time in tropical waters would generally indicate that you are a newer diver that has not yet got to a relaxed state when diving and air using a lot of air. Bigger tanks can extend that, but you will find that as you progress your air consumption will drop significantly.
I use my 130 strictly for live aboard trips where I will be taking photos and like to have a lot of gas so I can suck air down while kicking in current to get the shot I want. For regular dives I very much prefer a smaller tank such as my LP95's.
Dive time depends on a lot of things. You would have 50 CF more air with a 130, so you would get about 60% more time than with an 80 if all conditions remained the same. Dive time will vary with depth, with stress, and with effort expended while diving. You use a lot more air on deep dives than on shallow. Based on what I have seen, your dive time will increase substantially after you have more dive experience. The 130s are heavier than 80s or 100s. Here is Puget Sound most divers use 100s. I bought 120s when I started diving so I could keep up with my buddies, but now I always have surplus air when we end the dive. Cold water will create extra stress until you get used to it. If you dive a dry suit you will also be using some of your air in the suit.