[Rhodes22-list] Curved Rudder | 84 Rhodes 22

[Stan Spitzer]

Hard not to pipe in.

Other than prototype boats with aluminum rudder blades that did bend, 
all Rhodes rudder blades have been made with fiberglass and sized at 1 
1/2" to snugly fit between the rudder cheek panels of the rudder head.  
The blades are extremely stiff and would break before they would bend to 
any significant degree.

True:  In early Rhodes the centerboard and rudder blade were from the 
same mold.

Inaccurate:  We later created a /*different*/ mold for the CENTERBOARD, 
not a different mold for the rudder blade. We thereafter called the 
centerboard, the diamondboard; this because a horizontal slice through 
that part of the new board in the water, was an asymmetrical diamond 
shape; that shape based on the theory of naval architect Nils Lucander.  
We went to this design for 4 reasons:

Draft reduction:  While the Rhodes sails reasonably well on just the 
keel alone, when electing to sail with the "board" fully down the Rhodes 
would now be able to sail in about 6 inches less water.

Maintenance:    In order for the control line on the original board to 
not "hum", its pendant was attached high up the trailing edge of the 
blade.  This required the employment of a 4:1 mechanical advantage; a 
mechanism that, while made of stainless steel and plastic, ended up with 
a shorter life span than in concert with the rest of the boat. The 
"diamondboard" is controlled by a simple direct pull amazingly long 
lasting pendant system.

Safety:  We heard occasional horror stories of owners, sailing in 
accommodative water with their board fully down, having the boat raised 
by a wave or motor boat wake and then coming down so the board hit 
bottom and was then thrust straight up and through the centerboard 
trunk's cap.  This can never happen with the diamondboard's trigonometry.

Efficiency:  I am not convinced planes fly because of lift created by 
the shape of their wings.  That would go against planes being able to 
fly upside down?  So I am less convinced that boat fins create "lift" to 
allow them to point, since water, compared to gaseous air, is a lot less 
compressible.  Lucander's take is that it is the area of the fin that 
resists lateral thrust, compared to the area of the fin that creates 
turbulence, that is the marker for efficiency.  (I don't know. My first 
semester at Purdue was when we first bombed Berlin and a lot of climate 
change has been going around since then.)  A"match" race would be 
interesting, if we could find two Rhodies with identical racing skills 
or, who lacked motivational influences so we could rotate them in two 
match tests.  But even then the two Rhodes would have to have been built 
identically and every Rhodie knows that has never happened.

stan


On 11/26/18 6:41 PM, ROGER PIHLAJA wrote:
> Graham/Bob,
>
>> “In the beginning” ... The centerboard and the rudder blade we’re the same identical foil.  It was a very hydrodynamically efficient high aspect ratio foil.  At some point in the 1980’s (?) Stan changed the designs of the centerboard and rudder blade.  So, if you have a 1976 boat, your rudder blade is going to be thinner vs a newer boat.  Stan claims the new rudder and centerboard offer better performance vs the older parts.  But, that claim flies in the face of hydrofoil theory, so I’m a little sceptical.  I’d love to see an old vs new boat match race.
> Bob, I may have misunderstood something.  Did your boat come with a bent rudder blade or did you notice the bend recently after the boat was sitting on the trailer.  In the picture, it looks like the boat has sunk into the ground loading up the rudder blade.
>
> Roger Pihlaja
> SV Dynamic Equilibrium
> Sent from my iPhone
>
>