- Reading in the Basic Scuba book, there are two types of Scuba tanks referred to as "38's". I've pictured both in the photo above.
- On the left are U. S. Divers 38s. These have a working pressure of 1800 psi with 38 cf of air per tank. Filled 10% over they are about 41.9 cf.
- On the right are Sportsways 42s. These have a working pressure of 1880 psi with 38 cf of air per tank. Filled 10% over they are about 42 cf.
Big Buoyancy Difference
- My first dive with the Sportsways tanks was a surprise after diving with seemingly identical set up from USD. I wear 8 lbs of weight with the USD 38s. With the Sportsways tanks,I sank pretty good with the same weights. Took off two lbs and still sank heavily. And it got me to thinking.
- Basic Scuba lists the internal volume of these tanks. The USD 38s are 535 cu inches. The Sportsways 42s are 505 cu inches. External dimensions are awfully close and I don't think a difference in water displacement accounts for the difference in buoyancy. I think the Sportsways just has more steel.
- I did a little test to see how much they weigh in water. I used a very nice digital fishing scale and suspended each set of tanks underwater full of air. Basic Scuba says 84 cf of air weighs 7.2 lbs.
- Sportsways weighed 7.9 lbs which would be -.7 lbs when empty
- USD weighed 2.4 lbs which would be +4.8 lbs when empty. I also noticed that the USD tanks floated bottom up.
The REAL 38s...- The USD 1800 psi 38s are truly unique in being a twin set of tanks that won't sink you to the bottom if you dive without a wet suit. The Sea Hunt episodes where Mike Nelson wears twin tanks plus a weight belt... They could only be with the buoyancy profile of these type of 38s.
- I know with modern dry suits, many divers prefer tanks that are heavier in the water but, I prefer the USD 38s buoyancy. I like the idea of having the only thing that makes me sink be the weight belt.