This was inspired by a combination of Dr. Bob's and the equally
esteemed
Maxwell Buchananan's annotations on the linked idea.
The water-pogo apparatus consists of a long, stiff rod (no giggling
at
the back, please) - perhaps 10-20m of your finest carbon fibre.
Atop
this rod (for vertical
it is) is a securely-affixed chair equipped with
a
safety harness.
At the bottom of the pole is a hollow cigar-shaped tank, looking
rather like a fat spearhead on the end of the rod. The tank has a
displacement of maybe a tonne (of water), but weighs only a
fraction of this.
The Water Pogoer (or indeed anyone who wants to go pogo) is
strapped into the chair, and released from a great (but carefully
calculated) height over a deep body of water.
They plummet to earth and, with any luck (and some
aerodynamics)
the pole remains upright, causing the hollow tip-tank to pierce the
water at an impressive speed. Its streamlined shape means that it
enters the water without sending a massive impact through the
pole,
and it continues to descend rapidly below the waves, slowed by a
combination of hydrodynamic drag (hopefully modest) and
buoyancy
(hopefully large).
If the calculations have been done right, the weight and
momentum
of the Water Pogoer will carry the tip-tank down and down, until
it
finally comes to a halt when the pogoer's chair is only inches from
the water surface.
We now have an interesting situation. What we have is a man
sitting
on a chair, stationary at this instant, a few inches above the water
surface. Below the chair is the pole
and, at the far end of the pole many metres below the waves is a
hollow tank with a buoyancy of about a tonne.
The events of the next few seconds should be fairly self-evident.
The exact height to which the Water Pogoer will be
catapulted by the violently-breaching tip-tank will depend on
things
like drag and mass, but he and his pole should clear the water by a
quite impressive margin, allowing the entire spectacle to be
repeated again and again, at ever diminishing heights.