From: "Ian Macmillan" <iandmac@tpg.com.au>
Subject: A Gedinghyn experiment
Date: Tuesday, 11 October 2005 10:23 PM

A dinghy is fitted with a long horizontal cylinder with an >open end below
the waterline at the stern. .etc etc

Mein kleine gedankenexperiment mit ein beiboot!

Richard Feynmann's experience with the sprinkler had the same theme, and
proved again that experiments win arguments.

Long, long ago, probably pre WW2, you could buy a toy tinplate boat which
had a small coil of copper tubing, each end of which protruded underwater
from the stern. A spirit lamp heated the coil. Steam pulses ejected water
leaving a vacuum to suck in water and repeat the cycle, propelling the
model. It might have been called a Putt-Putt. Such a toy would probably
be banned today as too dangerous and likely to interest children in
science.

What brought all this to mind was reading about some very early steamship
experiments. One of these, by Denis Papin in France in 1707, involved a
pumping engine on a boat, the pumped water driving paddle wheels. A
hydraulic transmission yet! It seemed to me that, had it been thought
of, some type of reciprocating water jet might have been more effective
in the context of the time.

The reciprocating jet is probably quite efficient, but not terribly
effective. You can improve it by making it double acting, suck from the
front, and so on, but what you lose is its fundamental simplicity.

Similarly I resisted the temptation to analyse the operation of the
device in terms of the conservation of momentum, Noethers theorem, and
hyperbolic geometry, leaving these matters to those skilled in the art.

All the best
Ian Macmillan