[C320-list] Neutral or Reverse

[Jeffrey Hare]

At risk of beating this to death.. :)

There have been research studies at various universities on this very topic
of whether a freewheeling or stationary prop creates more drag.  Here's one
such study:  http://www.goshen.edu/physics/PropellerDrag/thesis.htm   But
this one is for AIR, not water and not being a fluid dynamics expert, I
can't say if they are related in any way.   I believe MIT had some studies
of boat props on this topic.

"The answer is complicatedly simple: it depends.".   :)

It depends on the size of the prop, the pitch, and the forward speed.

A stationary prop follows some curve of drag force, and a freewheeling prop
follows a different drag curve.

There is usually a crossover point, below which some props of some
size/pitch would be better freewheeling, where others would be better
stopped.

With some size/pitch props there isn't a lot of difference, others the
difference is quite pronounced.

-Jeff

-----Original Message-----
From: Quentin Murphy [mailto:qmurphy at sympatico.ca] 
Sent: Monday, March 26, 2007 9:10 AM
To: C320-List
Subject: Re: [C320-list] Neutral or Reverse

Some have said "Neutral or Reverse", but not never "Forward".  Why not?
Does it damage the gearbox or cause the engine to suck in water through the
exhaust or what?

Quentin Murphy
Celtic Knot #667

-----Original Message-----
From: c320-list-bounces at catalina320.com
[mailto:c320-list-bounces at catalina320.com]On Behalf Of donauw at bellsouth.net
Sent: March 26, 2007 8:28 AM
To: C320-List
Subject: Re: [C320-list] Neutral or Reverse


Lots of discussion.  Little data.

Been too windy in the Keys to try to get data (25 gusting 30 is fun sailing
but too inconsistent to get data that will probably differ by decimal
knots).

Numbers, anyone?

Regards,

Don Dixon
Stargazer, #605
Washington Island, WI (C320)
Big Pine Key, FL (C270)