Rocket Ascents... Can divers breach like a fish (split from Accident in Mich)

[rockjock3]

The other comment has to do with whales breaching. Whales, of course, attain a certain velocity when they breach...but they can continue to propel themselves with their flukes even AFTER all of their body (except the flukes, of course) has risen above the water. Kind of like water polo players who can keep about half of their body out of the water even though they have no vertical "velocity"...just kicking & sculling against the water to keep high in the water.

Good point. I was just thinking about pure velocity and didn't even think of the added point that dolphins and whales have the additional advantage of still using their tails until it clears the water.

 

[Somethin-Fishey]

I have seen the videos of guys in the training towers. 100ft and their feet are right the the waters surface, they have no wetsuit and no SCUBA gear, so I would think fins clearing are next to impossible.

Here is an old link:

http://www.scubaboard.com/archive/index.php/t-45913.html

 

[Blackwood]

Secondly, have you ever felt a whale's or dolphin's skin? Much smoother than ours and not all the pores to increase surface friction.

Small bumps may be better than perfectly smooth from a drag perspective.

 

[D_B]

While dimpled surfaces work well on golfballs (and even aircraft) , I do not think it would work in such a dense medium as water ... or maybe the dimples would need to be smaller ? ... hmmm

DB

 

[Blackwood]

While dimpled surfaces work well on golfballs (and even aircraft) , I do not think it would work in such a dense medium as water ... or maybe the dimples would need to be smaller ? ... hmmm

DB

I wouldn't say it's a density question. Some submarines use similar vortex generators. The goal is to energize the boundary layer so it stays attached longer (thus shrinking the wake and reducing form drag). Bumps cause the flow to become turbulent, and the eddies pull higher speed flow into the boundary layer.

 

[MXGratefulDiver]

Well, got to witness a rocket ascent from the beach today. From the DM who was accompanying the couple, the lady diver signals she needs to go up, grabs her inflator, and inflates it all the way, propelling her to the surface rather quickly from about 30 fsw. When she broke the surface, with a completely full BCD (you could hear the OPV popping), she barely came out of the water to her waist ...

... Bob (Grateful Diver)

 

[GreenDiverDown]

Well, got to witness a rocket ascent from the beach today. From the DM who was accompanying the couple, the lady diver signals she needs to go up, grabs her inflator, and inflates it all the way, propelling her to the surface rather quickly from about 30 fsw. When she broke the surface, with a completely full BCD (you could hear the OPV popping), she barely came out of the water to her waist ...

... Bob (Grateful Diver)

You can't expect a newbie to properly execute a Ralph Kramden...it takes lots of practice. :laughing:

 

[Gac]

OMG my sides hurt. From tachyon particles to flux capacitors to nozel-shaped anuses, it sounds like most possibilities have been explored. My own calculations based on simple newtonian physicas (and double checked by my physics-majored roommate) is that a person would have ot have an initial velocity leaving the water of about 7m/s, assuming a person around 6' tall. That's also assumes perfect exit with no additional resistance encountered during the splashy launch (unreasonable). That's pretty damn fast.
I'm going to see if I can get another friend to run a fluid-dynamics model working for this in his engineering lab. I'll get back to you on that, but initial estimations from the lab and it's members is a resounding "no, unless aditional forms of propulsion were applied."

Where's RecDiver?

 

[serambin]

No, but try this: propel a 180 # object and a 2 # object straight up,at the same speed and see which one stops traveling up first. Just a guess, but I think that the heavier object would cease to travel upward sooner...........I can't believe I got sucked into this thread!!!!!!!!

Yes, sucked is the operative word. :dry:

 

[teknitroxdiver]

I wouldn't say it's a density question. Some submarines use similar vortex generators. The goal is to energize the boundary layer so it stays attached longer (thus shrinking the wake and reducing form drag). Bumps cause the flow to become turbulent, and the eddies pull higher speed flow into the boundary layer.

Airplanes also use this technique...vortex generators just aft of the leading edge of the wings in the form of a row of small 'blades' set at alternating slight angles to the airflow. They keep the flow attached a lot farther back toward the trailing edge at lower speeds.