Foil Rudders
New replacement I-20/M-20 foil rudders are available for US$750. fob Minnesota, for a pair. These are made with I-20 class legal aluminum (6061T6) shafts, and the blades are made with Gougeon's epoxy, together with carbon fibre and glass reinforcement. Guaranteed not to drop off the boat for 5 years. Although not endorsed by NCESA (E scow), these will work on an E scow, and will work a whole lot better than what they are using now.
The prototype foil rudders for the I-20 were made by Phil's Foils in fall of 2009, shown here.
A comparison photo between the 'maximum' rudder allowed by the old Rule (12 inches x 15 inches), and an example of what can be made now under the new rule, which permits any profile, as long as it fits into a box/parallelogram that is no more than 17.5 inches deep, and 12 inches fore and aft. The Rule does not specify a foil plan profile, but the new blade, shown on the right, is an NACA 0012 section. 'NACA' is the National Advisory Committee for Aeronautics, and is the predecessor to today's NASA. The terminology '0012' breaks down as follows: '00' means that the foil has no camber, i.e., the foil is not bent or curved like a typical airplane wing, and the '12' means that the maximum foil thickness is 12% of the chord length. The chord length is about 12 inches in the rudder shown above. The maximum foil thickness typically occurs in an NACA section 30% aft of the leading edge of the foil, and this example is no different. To use the common NACA parlance, the I-20 foil is a 'symmetrical 4-digit foil'.
The old rudder, shown left, is now derisively referred to as the 'Domino's Pizza Box' design.
More on the NACA airfoil, from Wikipedia:
http://en.wikipedia.org/wiki/NACA_airfoil
The old rudder, shown left, is now derisively referred to as the 'Domino's Pizza Box' design.
More on the NACA airfoil, from Wikipedia:
http://en.wikipedia.org/wiki/NACA_airfoil
Why foil rudders are far superior to flat plate rudders. Shown here during testing November 21, 2009 (note the beach attire), we have tested a 'bisexual' boat...new foil rudder on Port, old plate rudder on Starboard. In this exercise, we have set the spinnaker and 'loaded up' the helm by sailing a bit too high, although without any excessive heel. Note the 'rudder boil' exiting under the transom. The rudder is turned to head down, but the boat isn't responding. Foil rudders rule.
The new rudder, on port, original flat plate aluminum style on starboard.
New foil rudder, 17.5" deep, versus old aluminum plate at 12". Which do you think works better?