The way SC and ARC and RC board and rudders ends are finished is the lowest drag and the toughest tip to put on the end of CBs and rudders.
This part makes great sense as I have been known to put the toughness of these boats to the test. I will say they can take a far better pounding then a few other boats.
Bill,
I have been studying your latest posts and I am always glad to learn from you. I think I understand the original question about the leading edge of the rudder being curved back to the trailing edge. At some point you refered to a rudder on one of our boats and if its not all the way down, with the leading edge vertical, that it would not be efficient.
Here is what I believe is the answer, but I don't claim to be a rocket scientist, so don't shoot me if I'm wrong.
The axis of the rudder on an AC 45 is actually in the center of the blade, parallel to the trailing edge. If the axis was at the forward most point it would be very hard to control and most likely would break.
On one of our rudders, the axis is just in front of the leading edge of the rudder. If it is not all the way down with the leading edge vertical, the rudder becomes much longer and therefore much harder to control.
Hello John,
The leading edge of your rudders should be forward of vertical. If you extend a straight edge straight down aligned with the pintle axes, it should cross the leading edge of the rudder first and as it extends further down it will cross the bottom edge. This should put about 15% of the rudder area in front of the extended pintle axis. This 15% rudder area is called "balance area" and it generates a torque opposite in direction to the rudder area aft of the pintle axis. This gives the boat a light helm, an easy touch. The other thing this swept forward leading edge does is it prevents "ventilation". At high speed if the leading edge of the rudder is swept back even very slightly, the water that impacts the rudder on leading edge centerline will flow, be pumped, down the leading edge, vertically down the leading edge. At speed this pumping action becomes so strong that it sucks air down the leading edge and the air will encapsolate the rudder and the rudder will no longer steer the boat. You will also hear a swoooooshing sound and the tiller feels like it is attached to nothing.
Since the AC boats have a rudder post built into the rudder blade near max thickness, they have balance area also.
The AC boats have the rudder mounted forward of the transom a few feet, therefore the top of the steering rudder is not exposed to air and it can't ventilate. They just pump water which is a small parasitic drag and it also increases the size of the rudder tip vortex.
Bill
We have a spare set (2) of SC17 rudders that have the 'extra' lock-down 'notch' which I assume (we have never used them) provides 'some' steerage (vs all the way up) in shallow water/surf.
Might you share some history of this rudder design and its proper function?
Thanks!
franklin Viola
Franklin you have it right. The shallow knotch is for steering in shallow water. After all , we talking about "BEACH CATS".
This idea seems to have been forgotten on newer boats. The game now is to build the rudder head as light weight as possible.
I have watched the newer boat designs try to sail away from Jensen Beach in the Tybe 500 Race. The sailors lean too hard on the rudder head designs that provide little to no support for the rudder in a part down position and they split/crack the rudder heads and or break the top off the rudders. The designer of these boats/parts forgot that they were designing "BEACH CAT" parts.
This isn't the whole story yet.