On Wed, 31 Mar 2004 10:20:59 +0100, "JimB"
wrote:


Steven Shelikoff wrote in message
...
On Tue, 30 Mar 2004 08:04:41 -0700, Keith Hughes
wrote:

enormous snip

Sorry to interrupt this thread, but you may remember a little
earlier I said I'd go away and play with fans, bits of card, bits
of wire and smoking fag ends to get my brain around this. The
idea was suggested by a very reasonable post from Derek Rowell.

Just to settle it for myself, once and for all, I just did my own
experiment. I have a fan in the living room. It's about 12" in
diameter. I got a light plastic spatula from the kitchen. I turned the
fan on high and hung the spatula blade in front of the fan free to swing
in all directions while I was controlling the angle of the blade to the
fan. As expected, when I rotate the blade left, the spatula swings
forward and to the left. Rotate right, it swings forward and to the
right.

So I hung the spatula just behind the fan. Lo and behold, the same
thing happens but just a little less. When I rotate the spatula to the
left, there is a noticable *left* motion to the blade... i.e., it's not
only drawn forward into the blade but it also moved to the left from
where it was when the spatula blade was perpendicular to the fan. When
I turn it to the right, the spatula swings to the right.

That proves to my satisfaction that if the rudder is close enough to the
prop, it's direction will have some effect on the motion of the boat
when you throw it in reverse even before the boat starts making sterway.

Steve