Drag !!! ?????

[Butch103]

Ok folks, I have read many threads on this board and time and time again people have mentioned reducing the "drag". Having gear streamlined to reduce snagging, coral damage and other such ideas make sense to me. However the "drag" issue boggles my mind. Help me to unboggle it. I can see the sense in reducing drag in any type of racing or timed event. But in Scuba ?? My scuba is not timed. Yes my bottom time can be limited to my tank size (volume) and my SAC rate. Sometimes I can stay down longer than the air in my tank allows..(eg shallow dives)...But how much more bottom time do you get by taking off the snorkel ( no I do not dive with mine, I don't like th epulling onmy mask)...Are talking the pulling sensation on the mask ?? Or actaully reducing the "drag" for more "air" time ????

Help !!!!! Inquiring minds need to know......:boom:

 

[Stone]

Drag is a force that is related to velocity. . . either your velocity through the water, or the water's velocity (current) acting on you.

No velocity = no drag. . . increased velocity = increased drag.

I can see the sense in reducing drag in any type of racing or timed event. But in Scuba ??

Imagine all you want to do is float around and look at the pretty fish. If there is no current, it hardly matters if you are streamlined or wearing a parka over your BC.

If there is a current, a streamlined diver will have a much easier time just staying in one place than a diver who is not streamlined.

 

[MechDiver]

I think the drag issue pertains more to tech diving where scooters and penetration/overhead diving is involved. I would think wearing a snorkle while using a scooter would not be a fun thing. Entanglement in this type of enviornment is a very high priority, and streamlining to reduce drag also streamlines to reduce entanglement.

Regardless of the "drag" issue, having your equipment streamlined and under control should be something you strive for every time you dive. Goes along with "if you don't need it, don't take it". I dive doubles as much as I can, and, granted, drag when you're wearing doubles, drysuit, canister light, etc. is a highly subjective matter. Still, I figure every little bit helps.

Phil

 

[Spectre]

The more drag you have, the more work it is to swim with your rig. The more work, the more air you suck. the more air you suck, the higher your SAC rate. The higher your SAC rate, the shorter you dive.

Not to mention that larger the breathing rate gradient between the work at depth and the rest of decompression [or safety stops] the less effective. e.g. if you 'on gas' by breathing twice as fast as you are when you off-gas, you're not going to have offgassed at the same rate...

[there's a thread about that somewhere... I'll try to find it].

 

[Uncle Pug]

As Stone pointed out even when you want to go slow.

And of course when you want to go faster and cover ground.

But the real deal is the extra un-noticed work it makes you do and with that comes increased SAC and increased CO2.

 

[weight_for_me]

..that there won't be any more complaints about Scooter and I going too fast for you???? lol
Randy...

 

[Scuba]

Water is approximately 784 times more dense then air at sea level. For someone used to moving about in air, this presents a huge increase in resistance to movement, requiring much more energy to move at the same speed in both substances.

For example: Driving in a car at 60 mph with the windows open, place your hand out the window with your palm flat and fingers held together (very carefully, only when and if safe), you will notice it takes a lot more strength to maintain your hand in place than if you where to do this while walking. Now move your hand through the water, it also takes great effort.

So even though you are traveling very slow underwater, the resistance you encounter is equivalent to moving through the air very fast. Hence your body, and anything you carry attached to it is going to significantly increase your resistance to movement.

Think in terms of aerodynamics in racing to minimize the drag of all your gear, body positioning and fin kick drag.

 

[rcohn]

As I've posted once before:

Drag force = (Cd)(A)(rho)(U^2)(0.5),
Where:
Cd – coefficient of drag (1.2 for a cylinder)
A – projected area in the plane normal to the flow
rho – fluid density
U – velocity
From: Streeter and Wylie, Fluid Mechanics, McGraw-Hill, pg 281, 1975. (This equation will be found in virtually any fluids text.)

Drag is a function of velocity squared, therefore it increases exponentially as you swim faster.. This means that you will fight a very high drag force as you swim faster or swim against a current. Streamlining reduces the projected area and possibly improves the drag coefficient. IMO every little bit helps when fighting currents.

Ralph

 

[Stone]

rcohn once bubbled...
From: Streeter and Wylie, Fluid Mechanics, McGraw-Hill, pg 281, 1975. (This equation will be found in virtually any fluids text.)

Good ol' Streeter and Wylie. I remember it like it was . . . 20 years ago.

 

[weight_for_me]

rcohn once bubbled...

Drag is a function of velocity squared, therefore it increases exponentially as you swim faster.. This means that you will fight a very high drag force as you swim faster or swim against a current.

..in other words..to go 2x as fast, you have to swim 4x harder:brain:
Randy...