[MHml] Cat Rudders Toed In?

[Glenn Brown]

Paul Nudd wrote:
> Half a degree? You can measure that accurately?

Sure, with 2 people: Just line up one rudder roughly fore-and-aft and 
measure the difference between the center of the leading and trailing 
edges.  For rudders that are 6" (254mm) front to back, 1 degree is 1/8" 
(just over 3mm)

Play is not an issue if you slightly side load both rudders in the same 
direction when measuring.  Ackerman is not an issue if the rudders are 
anywhere close to centered.

 > If there is play and they are set up parallel then they will
> 'flutter'.

IMHO, this play-induced flutter argument makes no sense.  If it made 
sense, people would also toe-in their daggerboards on typical cats, 
which keep both daggerboards down.

On points of sail where either rudder experiences zero side load [when 
reaching at some angle], play is not eliminated for that rudder.  Toe-in 
can only eliminate the case of both rudders experiencing play *at the 
same time*.

Also, upwind and down, you have weather or lee helm on both rudders if 
your boat is properly balanced, and the helm (rudder side load) 
eliminates the play on both sides.

Finally, If flutter occurs due to play, it will also occur without play, 
due to flex, though perhaps to a lesser degree.  So, if you experience 
flutter there is probably something fundamentally wrong with your foils, 
such as not being designed to twist appropriately when side loaded.  I 
mean, who has ever heard of properly designed solitary rudders 
fluttering voilently when you introduce play by letting go of the tiller?

So, the only place I can think where using toe-in to eliminate flutter 
makes any sense would be if someone were constantly balancing their rig 
for neutral helm; but I believe this is never the most efficient way to 
sail to weather, since foil drag is generally minimized to weather with 
an approriate amount weather helm.  I hope no one is doing this!

--Glenn