Just to fill people in on some conversations between Bram and myself regarding
the construction of rudders. And to clean up some of the Rules which are left a
little vague before the ISSA gets to its business.
One of the central aims of the class is to spec a high quality, easy to sail,
boat at a reasonable cost. Rudders in particular were singled out in the rules
because they have the potential, if made badly or too extreme in section or
area, to make the boat hard to sail (sometimes for apparently inetrmittent and
unfathomable cause). For this reason the efficient and conservative 49er class
rudder was used as a prototype. Since we are all having trouble getting 49er
rudders I undertook to make a foam core workalike so that you can make a
standardized rudder at a substantially reduced price. This required some
tradeoffs in planform shape.
For those who may not be aware the 49er rudder has a planform shape that tapers
to the tip from 2/3 of the leading edge depth. From the trailing edge, the arc
taper starts at 1/2 or less of the depth. On the older 49er rudders (like mine
it starts higher up and since these appear to be shaped by hand it's hard to
approximate the radius. In order to make the boards cheaper using foam cores
the radii need to be modified or approximated. Since foam cores can only be cut
with straight edges one would need to increase the number of cuts, and the
cost, to get an exact or very close approximation of the 49er board. There has
been a lot of to-and-fro on the planform issue and we feel that the NYC Skiffs
Rudder core planform, or something similar, is a reasonable compromise that,
importantly, maintains the exact 49er section shape and the total wetted
surface of the rudder. Moreover, the center of vertical area is in
substantially the same place to maintain the feel. Now that class members and
the two (or 3) commercial manufacturers have blades based on these cores in
production, I think its time for ISSA to issue a standard, under Rule
5.13.6e(ii), so that the foils will be technically legal as well as within the
spirit of the rules.
5.13.6e. The rudder shall match the profile and section defined by these class
rules.
i. The official rudder foil of the International 49er class shall
be acceptable.
ii. Alternatively, rudders may be built to comply with the section
and profile
designated by ISSA.
iii. Rudders built to tolerances that fall between the official
ISSA sections and
profiles and those of the official 49er rudder shall be acceptable.
In lieu of a functioning ISSA until the elections in March 2005, I'm calling on
the designer to designate the Specs for our own (ISSA) class rudder. I will
make sure the cores respect exactly these specs.
Greg Ryan
Swift Solo --Rose
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