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

[japan-diver]

The theory is easily tested freedive down to the desired depth, put gear on hit inflate button.(Do not breath from reg) Since its a freedive no embolism worries. Did this for fun a few years back with a Zeagle tech BC from about 30ft with a 3mm wetsuit got to about waist level finning all the way. I may now have to go back and try it with my drysuit now just to see. Have been a safety diver for a few competitive free diving competions -using lift bags to come up very quickly competitiors will hit the surface and come out to about chest level usually.

Now an expert freediver with a monofin, finning up can clear the water, fins and all. But they are continuing to kick after the chest and waist clear the water- have seen this on video and been able to get to about knee height myself. This also requires a bend at the waist and pulling the feet out at the perfect time to be "clear" of the water for a milisecond before going back in head first. I believe this is on Terry Maas's (sp) video on free diving technique and the diver is a female from Hawaii.

 

[DiveGolfSki]

I've also heard it called hull speed. This applies to displacement hull boats only, not planing boats.

http://www.sailnet.com/collections/articles/index.cfm?articleid=colgat006

It is called hull speed. It calculates Maximum Speed of a Single-Hull
Displacement Boat:

Hull Speed = 1.34 * (LWL)1/2

LWL: length of the hull at the waterline. Note that the 1/2 is means to the power of 1/2.

 

[Blackwood]

i agree with the terminal velocity bit, but it bigger engine-same max speed seems counter-intuitive. is it the drag that slows you down- more power generates proportionately more drag?

As you increase velocity, the power needed to overcome drag increases as a cubic function.

 

[Blackwood]

Wow, you learn something new each day. Out of curiousity, how would adjusting the materials on the diver, say with dimples as blackwood suggested, affect this? I am guessing it would change the theoritical max speed?

Can this be related to air and say aircraft? If there a theorical max speed (excepting the speed of light) that can be calculated?

The dimples are an effort to shrink that low-pressure region he was talking about.

Golf balls have dimples so they will go faster. Tennis balls have fuzz for the same reason. I gave a brief quasi-technical explanation of what's happening in a previous post.

But yes, it can be related to air and aircraft. As teknitrox mentioned, vortex generators are generally not used to increase the maximum speed of an aircraft, but rather to make sure air will flow over the control surfaces. But the principle is the same. Higher energy air is less likely to seperate from the surfaces. Less air seperating = smaller wake = less drag.

(more-or-less)

 

[MXGratefulDiver]

The dimples are an effort to shrink that low-pressure region he was talking about.

Golf balls have dimples so they will go faster. Tennis balls have fuzz for the same reason. I gave a brief quasi-technical explanation of what's happening in a previous post.

But yes, it can be related to air and aircraft. As teknitrox mentioned, vortex generators are generally not used to increase the maximum speed of an aircraft, but rather to make sure air will flow over the control surfaces. But the principle is the same. Higher energy air is less likely to seperate from the surfaces. Less air seperating = smaller wake = less drag.

(more-or-less)

Gee ... I guess it really IS rocket science ... :umnik:

... Bob (Grateful :eyecrazy: Diver)

 

[bradshsi]

The dimples are an effort to shrink that low-pressure region he was talking about.

Golf balls have dimples so they will go faster. Tennis balls have fuzz for the same reason. I gave a brief quasi-technical explanation of what's happening in a previous post.

(more-or-less)

To be more precise the dimples on a golf ball modify the boundary layer. However experiments show that while the dimples reduce drag, more important is their effect on lift (improving the Magnus effect).

Unfortunately for our diver we're not really interested in that. Further, because air and water have such different physical properties, what will work in air is not necessarily good for water.

Some years ago in the Americas Cup (the sailing event), there was some controversy about the use of special underwater textured surface coatings to reduce drag. These took the form of a plastic film with tiny riblets aligned with the fluid flow. Apparently some sharks also have similar features on their skin.

Given that divers will operate in similar speed ranges this might be a better choice in your quest for drag reduction...

http://oea.larc.nasa.gov/PAIS/Riblets.html

 

[Diver Dennis]

To be more precise the dimples on a golf ball modify the boundary layer. However experiments show that while the dimples reduce drag, more important is their effect on lift (improving the Magnus effect).

Unfortunately for our diver we're not really interested in that. Further, because air and water have such different physical properties, what will work in air is not necessarily good for water.

Some years ago in the Americas Cup (the sailing event), there was some controversy about the use of special underwater textured surface coatings to reduce drag. These took the form of a plastic film with tiny riblets aligned with the fluid flow. Apparently some sharks also have similar features on their skin.

Given that divers will operate in similar speed ranges this might be a better choice in your quest for drag reduction...



http://oea.larc.nasa.gov/PAIS/Riblets.html

I'd like to meet the diver that can keep up with an America's Cup yacht.....

 

[lamont]

I'd like to meet the diver that can keep up with an America's Cup yacht.....

...or a shark.

 

[Diver Dennis]

...or a shark.

An even better point...

 

[bradshsi]

...or a shark.

True. But...

Americas Cup boats have to perform well in light air or out of a tack where they may move at only 1-2 knots. Similarly sharks can cruise fast or slow as the moment demands. The drag reduction is still there.

Besides we are trying to strealine our diver for his 21 ft/second ascent (If you don't know where that figure came from look at posts #55 and #155). That puts us very much in the same speed realm