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

[teknitroxdiver]

Not quite. By you calcuation I can apply an infinite force and still not get past 4 mph. Trust me, if you take any of the other suggestions, such as the advanced skill of the underwater tank valve removal emergency ascent (Padi I believe has a card for this), you will most assuradly exceed 4 mph.

No. As was said above, it doesn't work like that. There is a law in sailboat physics that for a certain hull size and design, you will have a max speed of x knots, regardless of if you put a 1/2 hp outboard or a 150,000# jet engine on it.

The only way to adjust terminal velocity is to adjust the design of the object.

 

[do it easy]

No. As was said above, it doesn't work like that. There is a law in sailboat physics that for a certain hull size and design, you will have a max speed of x knots, regardless of if you put a 1/2 hp outboard or a 150,000# jet engine on it.

The only way to adjust terminal velocity is to adjust the design of the object.

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?

 

[serambin]

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?

To explain what seems to be counter intuitive, as a body pushes through the water, a wave created by the front of the body moves aft as speed increases. As the terminal velocity is reached, the wave reaches the back of the body and 'sucks' the body backward. To overcome the reverse pressure requires a huge force. When a power boat exceeds this velocity it does so by skimming over the water (planning), but for bodies under water this is not an option.

Stan

 

[do it easy]

To explain what seems to be counter intuitive, as a body pushes through the water, a wave created by the front of the body moves aft as speed increases. As the terminal velocity is reached, the wave reaches the back of the body and 'sucks' the body backward. To overcome the reverse pressure requires a huge force. When a power boat exceeds this velocity it does so by skimming over the water (planning), but for bodies under water this is not an option.

Stan

ok maybe drag isn't the technical term, but if i'm reading this correctly, applying a bigger engine only increases the "sucking" force.

 

[SeanQ]

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

A beautiful example of hull speed can be seen whenever a tugboat is cruising to a job. They have tremendous power and very easily reach hull speed. The classical wave pattern of a bow wave and quarter wave is always present at that speed. For a tugboat to go even marginally faster would take so much more power it would be uneconomical. When a boat does exceed its hull speed, as the one being towed in Figure 5, the stern tends to leave the quarter wave behind and drop into the trough between waves while the bow rides high in the air. Often one sees a number of displacement one-design racing sailboats being towed to a regatta at greater than hull speed with their sterns practically under the water.

 

[D_B]

I still don't see how this relates to a submerged object with no waterline or wave hight ...

"as the speed increases, the bow has to push aside a greater the volume of water and the bow wave becomes larger. As the bow wave increases in height, the distance between its crest and that of the wave following it, the quarter wave, increases until it approaches the waterline length of the boat" ... "until, hull speed is attained and there are only two waves along the hull, the bow wave and the quarter wave. To push a boat past its theoretical hull speed, though possible, would take more power in wind and sails than most boats can withstand.

 

[Vtdiver2]

Did you do it from the 100ft dimple? They only let us do it from the 40ft ledge. I went for DC Olympics frm Portsmouth Naval Shipyard. The video they showed us, definitely had people coming out of the water to their ankles/feet.

At the sub school in Groton Conn they have a tower they use. They put 4-6 of us in a room, like an elevator, that had a hatch in the top. This was in the bottom of the tower. They started filling the room with water. When the room finished filling and pressures on both sides of the hatch equalized, we pulled the hatch open and one by one floated to the surface 100 ft above. I remember coming out of the water to my waist.
They no longer do this training, as they say based on the depths the subs go to, using this method of escape is very unlikely.
Chris

 

[in_cavediver]

To explain what seems to be counter intuitive, as a body pushes through the water, a wave created by the front of the body moves aft as speed increases. As the terminal velocity is reached, the wave reaches the back of the body and 'sucks' the body backward. To overcome the reverse pressure requires a huge force. When a power boat exceeds this velocity it does so by skimming over the water (planning), but for bodies under water this is not an option.

Stan

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?

 

[Heffey]

Here is some data that may be relevant here.

This is data from a record breaking freediving dive profile.

The dive was to a depth of 125 meters.

A float bag was used to bring the diver back to the surface.

It took 44 seconds ascend with a maximum ascent rate of 4 meter/second.

By my calculations this is a max speed of 8.95 mph.

 

[D_B]

I still don't see how this relates to a submerged object with no waterline or wave hight ...

"as the speed increases, the bow has to push aside a greater the volume of water and the bow wave becomes larger. As the bow wave increases in height, the distance between its crest and that of the wave following it, the quarter wave, increases until it approaches the waterline length of the boat" ... "until, hull speed is attained and there are only two waves along the hull, the bow wave and the quarter wave. To push a boat past its theoretical hull speed, though possible, would take more power in wind and sails than most boats can withstand."

Air is compressible , water is not. so I dont see how this can directly relate to an object under the water that does not have this air/water interface. Anyone have an explanation for this ???
DB