Speed control during a drift dive

[Charlie59]

We hope he changes his underwear more often, but we are not sure.

Use of your fins to slow or speed could be based on the "laminer flow" bands in water. If you extend your body profile into faster current farther from the reef or bottom you might go faster. If you extended your fins into bands going slower you could go slower.

Along the same lines, I have noticed moving faster with a larger bulker bcd than folks with smaller profiles during drift dives. Likely the drag is pushing wider objects to stay up with the current. It is not likely that the diver moves "as fast as" the current in most instances, but has a proportional speed to the current. The more of you there is to pull the faster you go.

 

[Charlie59]

Of course you understand, I could be full of poo.

 

[Cacia]

That's a bit like asking if you'll move faster along a conveyer belt if you lay down in a Superman position.

One situation has forces not in play on a conveyor belt.

 

[agilis]

The physics are too complex to generalize. Currents are not simply globs of water in linear motion, and drag can involve isues like weight, bouyancy, gravity and, of course, outside influences like turbulence created by all sorts of things, including temps, salinity, and proximity to solid objects, like the bottom. One's position in the current stream also has an effect. It is not possible to travel faster than the current unless you employ forward motion effort, like swimming. Running at an angle down wind in a sailboat can move the boat faster than the wind speed because the sail creates its own concentrated force of redirected focused airflow. Partial vacuums may also be involved.

Streamlining, or its opposite, has little effect on your speed while being moved by a water current.

 

[Cacia]

so you at least agree that it is NOT the same as a conveyor belt though, correct?

Streamlining, or its opposite, has little effect on your speed while being moved by a water current.

but placing your perpendicular to the current with dorsi-flexed heels would slow you some right? Like a sea anchor....

 

[Jcsgt]

Guess I should have paid more attention in physics class!

 

[TheRedHead]

What about the lard-butt factor? Does a larger mass move slower than a smaller one?

 

[Jcsgt]

What about the lard-butt factor? Does a larger mass move slower than a smaller one?

I always felt, when I had gained a few pounds, that I would actually drift faster and vice-versa. Maybe it was just my perception.

 

[agilis]

An untethered sea anchor just collapses. It needs the tension from an object on the surface to open it. Placing yourself in a spread eahle position perpendicular to the current direction should have no significant effect, unless your extension places you in two or more slightly different currents, creating turbulence. Changing your body position should theoretically have no effect, once the current has you and any inertia has been overcome. Moving in exact synchonicity with the current should feel like being in perfectly still water, except for the visual of fixed objects, like the bottom, flashing by. The weight or size of an object is of no relevance once neutral bouyancy is reached.

On sailing ships, when sailing by the wind at exactly the wind's speed, the feeling is that the air is virtually motionless, even if you are moving along at 20 knots, relative to a fixed point. This can be a very strange sensation, even uncomfortable in the heat, because there is no breeze, even though the wind is blowing strong.

 

[Hank49]

We hope he changes his underwear more often, but we are not sure.

.

I'm a product of the late 60s, early 70's hippie times....I don't always wear underwear.