Posted by tleemay on August 09, 2001 at 17:04:42:
Some anonymous poster was curious as to how a backpack diver would
compare to a streamlined BP/wings diver. At that time I asked the
original writer of the first streamlining data to calculate and
compare the two. Here is what he came back with;
At your request, I ran another set of calculations on the Drag Force (lbs) [DF/lbs] which would be generated by a diver in the water as a function of the current.
As I have stipulated previously, these are ROUGH numbers. I am assuming this test subject has perfect trim and is not moving.
Again, the test subject was 220 lbs and 76 inches tall. I ran 2 configurations. In each configuration, I ran single PST 104 tanks and an EE Pro 6 cannister light.
The Streamlined configuration was typical DIR in profile with a single piece harness and low profile single tank adaptor and 27 pound lift wing. The Back Pack configuration was a standard Scuba Pro ABS with normal shoulder and waist straps and no wing.
Current Velocity (kts) 1 2 3 4 5 6 7
Streamlined - single tank 9 36 82 146 227 327 446
Back Pack - single tank 11 43 97 173 270 388 529
Once again, these are ROUGH numbers. I hope these help you out.
Like I pointed out before, the number itself isn't that important, but
the difference between the two configurations is.
To me is looks as like the overall numbers are close enough at
typical swiming speed not to worry about with a very slight edge to
the BP/wings configuration. There is an obvious advantage to having
some weight on the plate. I realize that there is no wing involved on
the back pack, but I do know that the space between the tank and the
back is more or about the same depending of which STA the BP is using.
What I do know, is that in comparing this calculation to Tom's
previous calculations is that the diver's trim is in the water is
equally or more of a factor overall than what he or she is diving on
their back. The difference is, that with a BP/wing you have better
control of your buoyancy at the various depth - especially when loaded
down with game or goodies.
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