Rudder Vibration

[rcgamble]

hello I have a spade hung rudder on a 38 foot catamaran and at 1500 - 2500 rpms I get a noticable rudder tap and vibratio. The rudder has synthetic or plastic type caps for wear protection. The rudder is secured by a steel coller ring on top. When I run at 3000 rpms the vibration become minimal but still noticeble. Any thoughts.

 

[Randyonr3]

Prop wash

If your prop is forward of the rudder, its prop wash or turblance from the water comming off the prop.............