[Rhodes22-list] Curved Rudder | 84 Rhodes 22
Stan Spitzer
stan at rhodes22.com
Tue Nov 27 06:46:27 EST 2018
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
>
>
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