I'd guess all three ideas have merit. Consider the helicopter. That
WHOP-WHOP-WHOP you hear is the downwash from the rotor blades striking the
tail. The more space, the quieter.

Room to pull a prop probably includes space for the puller and clearance for
the blades when the rudder is deflected.

Roger

http://home.earthlink.net/~derbyrm
"Brian Cleverly" wrote in message
...
Mungo Bulge wrote:

http://www.yanmarhelp.com/i_propclr.htm

It makes sense all around. The need for an aperture is to allow smooth
flow of water into the prop, to reduce cavitation. Now that you have all
this smooth flowing water accelerated by the efficient prop, why spoil it
all by bumping into a rudder or other deadwood?


Well it eventually "bumps into the rudder" anyway...

IMHO, on a sailboat, rudder efficiency is far more important than getting
the last ounce of effort out of a prop.

Not only does an efficient rudder make handling easier but it also gives
some additional lift and that is precisely the reason for my question.

Brian C

"Roger Derby" wrote in message
ink.net...
| Could it be for clearance when the rudder is deflected?
|
| Roger
|
| http://home.earthlink.net/~derbyrm
|
| "Brian Cleverly" wrote in message
| ...
| Does anyone have any thoughts/theories on the reason for extending
the
| prop aperture into the rudder when the rudder is hung off the back of
a
| long-keel.
|
| I would imagine it would drastically reduce rudder efficiency, but
| possibly allow more of the prop to receive undisturbed water when
| backing-up.
|
| Thots anyone ?
|
| Brian C
|
|