Post by surflung on May 21, 2015 6:13:16 GMT -8
Twin 38s vs. Twin 42s
- I have three types of Twin 38s and I thought I'd share what I've learned about them.
- First, they are certified as either 1800 psi or 1880 psi working pressure. I have a set of military surplus 38s that are 1800 psi (left). I have a set of U.S. Divers 38s that are 1800 psi (center). And, I have a set of Sportsways 38s (aka 42s, right) that are 1880 psi.
- If you fill any of these to 10% over working pressure, they are roughly 42 cubic feet. 1800s at 10% over are 1980 psi, which is 41.8 cubic feet. The 1880s at 10% over are 2068 psi, which is also 41.8 cubic feet.
- The 1800 psi tanks are "floaty-er" than the 1880 psi tanks. I wear 8 lbs of weight when diving the 1800s with my 3mm wetsuit. When diving the the 1880s I wear from 0-2 lbs of weight to achieve the same buoyancy as the 1800s.
- I've been told that the 1880 psi tanks are heavier than 1800 psi tanks simply because they have more steel to match the higher working pressure. This is not a minor consideration when buoyancy is considered. For example, you can wear Twin 1800s and not sink when free diving without a wet suit... You may even need a weight belt. Twin 1880s on the other hand, will sink you when free diving without a wet suit.
- A 10% overfill figures into the original advertising campaigns of USD and Sportways. The original USD ads called their 1800 psi tanks "Twin 38s"... Even though a 10% overfill made them 41.8 cubic ft. The Sportways ads called their 1880 psi tanks "Twin 42s"... Even though they weren't 42s unless they had a 10% overfill to 41.8 cubic feet. USD then changed their advertising to call their tanks Twin 42s. (BTW - The VDH site has many of the vintage scuba catalogs available online in pdf format).
- I have three types of Twin 38s and I thought I'd share what I've learned about them.
- First, they are certified as either 1800 psi or 1880 psi working pressure. I have a set of military surplus 38s that are 1800 psi (left). I have a set of U.S. Divers 38s that are 1800 psi (center). And, I have a set of Sportsways 38s (aka 42s, right) that are 1880 psi.
- If you fill any of these to 10% over working pressure, they are roughly 42 cubic feet. 1800s at 10% over are 1980 psi, which is 41.8 cubic feet. The 1880s at 10% over are 2068 psi, which is also 41.8 cubic feet.
- The 1800 psi tanks are "floaty-er" than the 1880 psi tanks. I wear 8 lbs of weight when diving the 1800s with my 3mm wetsuit. When diving the the 1880s I wear from 0-2 lbs of weight to achieve the same buoyancy as the 1800s.
- I've been told that the 1880 psi tanks are heavier than 1800 psi tanks simply because they have more steel to match the higher working pressure. This is not a minor consideration when buoyancy is considered. For example, you can wear Twin 1800s and not sink when free diving without a wet suit... You may even need a weight belt. Twin 1880s on the other hand, will sink you when free diving without a wet suit.
- A 10% overfill figures into the original advertising campaigns of USD and Sportways. The original USD ads called their 1800 psi tanks "Twin 38s"... Even though a 10% overfill made them 41.8 cubic ft. The Sportways ads called their 1880 psi tanks "Twin 42s"... Even though they weren't 42s unless they had a 10% overfill to 41.8 cubic feet. USD then changed their advertising to call their tanks Twin 42s. (BTW - The VDH site has many of the vintage scuba catalogs available online in pdf format).