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

[MXGratefulDiver]

In the book the, "The Last Dive", the author recalls an accident about a diver who's drysuit fill valve stunk in the open position. His ascent, from a depth in excess of 100 feet, was so quick that eye witnesses said, "that his fins cleared the water upon exiting". The end result was that this particular dive ened up wheel chair bound from this experience.

For those of you that can not exceed 2 feet of clearnace from the water, I would suggest that you consider losing some of your extra weight before continuing to dive. Hell, I have seen whales clear more than that at the zoo.

I, too, have seen whales breach. But divers are not whales. We have heavy gear, exposure suits that provide a lot of drag, and not nearly the propulsion power of a whale. I'd be very skeptical of any claim that a diver can actually manage to get completely airborne simply by ascending too rapidly.

Think about it ... even an ascent of 500 feet per minute (83 feet to the surface in 10 seconds) is only about six miles per hour ... that's not nearly fast enough to force a total breach from as dense a medium as water. By comparison, a breaching orca will attain speeds of up to 30 mph.

... Bob (Grateful Diver)

 

[Rec Diver]

I, too, have seen whales breach. But divers are not whales. We have heavy gear, exposure suits that provide a lot of drag, and not nearly the propulsion power of a whale. I'd be very skeptical of any claim that a diver can actually manage to get completely airborne simply by ascending too rapidly.

Think about it ... even an ascent of 500 feet per minute (83 feet to the surface in 10 seconds) is only about six miles per hour ... that's not nearly fast enough to force a total breach from as dense a medium as water. By comparison, a breaching orca will attain speeds of up to 30 mph.

... Bob (Grateful Diver)

I just love you guys. Now assuming that the velocity is constant, which we know it is not...water pressure reduces as we ascend...increasing the velocity, calculate the energy of an average diver at that speed versus his weight ration, remebering that weight only becomes a factor once breached...in water we are weightless. Or, better yet, if you agree for just a moment that it is possible to breach, how fast would you have to be ascending to do so?

 

[Uncle Pug]

What a drag.

 

[pants!]

A quick off-the-top-of-my-head calculation says that the diver would need to be ascending at approximately 1000 feet per minute to get the fins out of the water.

 

[mstudley]

*edit* -- decided not to be a jerk...

 

[pants!]

OK so I actually did some math.

For an object to be projected 5 feet into the air against the force of gravity, it needs an initial velocity of about 17 feet per second, or 1020 feet per minute.

 

[MXGratefulDiver]

I just love you guys. Now assuming that the velocity is constant, which we know it is not...water pressure reduces as we ascend...increasing the velocity, calculate the energy of an average diver at that speed versus his weight ration, remebering that weight only becomes a factor once breached...in water we are weightless. Or, better yet, if you agree for just a moment that it is possible to breach, how fast would you have to be ascending to do so?

Is it possible to breach? Yes ...

Is it possible to breach to the point of becoming airborne? I don't think so.

And yes, the weight of your scuba gear will pull you down the instant you break the surface, and the drag will slow you down significantly before you get there.

A little "safe" experiment for ya ... go skin diving. Dive down as deeply as you can, then propel yourself toward the surface as hard and fast as you can. See how far out of the water you can force yourself to go.

Betchya you can't force yourself completely outta the water ... even without the weight and drag of scuba equipment ... and if you claim otherwise, I want to see the video ...

... Bob (Grateful Diver)

 

[pants!]

By the way, that's almost 12 mph.

 

[Rec Diver]

By the way, that's almost 12 mph.

No. Bob is correct, it is almost 6 mph, actually 5.65 mph.

 

[ClevelandDiver]

I just love you guys. Now assuming that the velocity is constant, which we know it is not...water pressure reduces as we ascend...increasing the velocity, calculate the energy of an average diver at that speed versus his weight ration, remebering that weight only becomes a factor once breached...in water we are weightless. Or, better yet, if you agree for just a moment that it is possible to breach, how fast would you have to be ascending to do so?

Enough math and theory, how about some actual testing.....

Fill a drysuit with water equal to 150lbs on land (water weight is obviously neutral in water). Exhaust valves should be in the fully closed position. Use dry gloves to seal the wrist and duct tape a water filled 2 liter bottle into the latex neck seal. Attach tank with back plate and harness, don't forget the crotch strap. Rig inflator to stick open once inflation begins. Bring the entire mess underwater and try your best to get lift off. If the inflator rigging is to big a bother, use a lift bag. Make sure to have a witness with a video recorder on the surface. Someone really needs to try this, it could be as big as the exploding tank thread!