The Pond Ness Monster

A vinyl toy head used for the Pond Monster.
Plastic 2 ft. alligator.
The inner construction of the Monster.
Monster head on flotation chamber.
Monster adjusted with 5 lbs.
Monster adjusted with 6 lbs.

   The dreaded Pond Ness Monster is ballasted so that it rises and breaks
the surface when a certain amount of air is inside it.  Until that point,
it patiently waits on the bottom of your pond.  After surfacing for a time,
it vanishes beneath the waves.  The air is supplied by tubing from an
aquarium pump on land.  Your "monster" can be an alligator, crocodile,
plesiosaur (Nessie), mermaid, "dead body", etc.
   The air bubble inside eventually becomes big enough to float the
structure. Soon the air bubble will dip below the bend in the copper
U-tube.  Now the weight of the structure forces water up into the air
chamber, pushes all of the the air bubble out, and it sinks. The air
exits out the monster's nostrils.  Then the cycle repeats.
   The weight of the structure, the size of the air bubble and the depth of
the bend in the U-tube determines how much of the figure is exposed when
surfaced.  The lid with a 3" hole cut into it was used on our 19-cup plastic
bucket so that slight tipping would not let any of the air bubble go out
under the rim prematurely.  Our lid had to be sealed with caulking.
  From the time our small monster begins to receive air to when it breaks
the surface is three minutes. It then takes about 15 seconds to reach full
height and then only about three seconds to disappear. The time above water
is set by the size of the air bubble. The time it takes to vanish beneath
the waves is set by the diameter of the U-tube.
   Of course, like any great stunt, the secret is to tell no one of your
monster.  At a family reunion or a wedding, secretly plug the air pump
in so that the monster makes its grand debut at the perfect time.
   Or you could make the pond monster into a clock by having it surface
on the hour by using a timer for the air pump.  It takes three minutes for
the monster to float, so allow for that delay.  It would also be necessary to
have the pump turn off after the release of the air bubble, when it descends.
If there was a partial bubble left inside, the timing would get out of synch.