Rudder Shape Without a rudder there is nothing to keep the transom from chasing the bow like a dog chasing its tail. The prop will walk the transom to the right no matter how well the hull is balanced and setup , the angular momentum of the motor and side thrust of the prop will see to that. The rudder provides the necessary side resistance to keep the transom in place.
 Now what shape should the rudder be for best performance? The current best of breed is the wedge rudder, but if you were to just look at the drag coefficients this would not be the correct choice. Elliptical shaped rudders with a 4:1 length to width ratio have a Cd of 0.32, bring that up to 8:1 and Cd drops to 0.29. Compare those numbers to a typical wedge rudder Cd of 0.8 to 1.0.
Now Lets assume a 40MPH boat one with a 1/16X1 elliptical and one with a 1/8X1 wedge rudder, using the below equation we would find a difference in drag of almost 2.5lbs! 
So why are we using these "high drag" wedge rudders, well there are several scientifically based reasons: - It generates a side load that counteracts the prop torque which allows the boat to track straight. It does this by keeping the water in contact with both sides of the wedge for its entire length which generates a side load which counteracts the prop walk effects.
- The shape propagates a low pressure area on the outside of the rudder even at very low angles of attack, this assists in turning, especially at high speeds.
- After the wedge ends the water separates very cleanly from the trailing edge which helps minimizes drag (keep those edges sharp)
- The wedge generates a water void behind its trailing edge. This void gets ventilated (filled) with air, air of course has a much lower drag coefficient than water due to the density.
 If you were to use an elliptical rudder you might have to keep some turn on the rudder to counteract the prop torque and allow the boat to track straight. That slight turn in the rudder and the resultant change in frontal area (A) can generate far more drag than a wedge rudder.
Should you ever use a blade rudder? The answer is a resounding maybe! For a SAW boat it represents the lowest drag and since turning is not an important consideration a blade rudder is your best bet. For oval racing boats it depends on both the boat and the speed, its pretty common to see blade rudders on 6-8 cell class boats. In those classes the smaller props have lower prop walk characteristics and a blade rudder might be your best bet. The best way to find out is to try both and see what works for you. I find my N & O class boats do great with a blade, but my P and LSH really like a wedge. Rudder Angle Does it matter how your rudder is angled on the boats transom? A rudder like any appendage in the water and can and does effect the trim of the boat. If you angle the bottom of the rudder away from the stern then you will generate an upward force on the rudder, lifting the transom and pushing the bow down. This is called a kicked back rudder. 
Conversely if you angle the bottom of the rudder towards the bow you will generate a downward force on the transom and lift the bow. This is called a kicked forward rudder. Today's newer swept wedge rudders provide a small amount of kicked back position by nature of their swept leading edge. This will help lift the transom and in theory make the boat run a bit faster if it is trimmed right. Rudder Tuning  There are a couple of simple things that you can to do to fine tune your rudder. The first is to sharpen the leading edge of your wedge rudder to help cleanly separate the water flow. Second round the bottom of a flat bottom rudder to eliminate its lifting abilities. Last round the front corner where the leading edge meets the bottom, this will reduce the drag.
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