View Full Version : Cavitation???Could it be the Rudder??

08-27-2011, 04:22 PM
I have posted several postings in the past related to cavitation we have been experiecing on our 2000 Kamberra. The cavitation is present in calm water, rough water, fully loaded boat or practically empty, towing etc... The cavitation was extreme when making right turns. This weekend we lost the rudder during one of the many cavitation experinces while making a right turn. I have already ordered a new rudder from skidim but wondering if that was the reason for the cavitation we were experiencing??? Any feedback appreciated.

08-27-2011, 10:15 PM
What do you mean , lost your rudder as in it fell off? Was it prop cavitation or engine cavitation. Prop cavitation will be experienced when air is introduced into the thrust angle as in certain turns , heavy ballast, rough and calm conditions, speed can be a factor as well as what you are pulling. And this assuming you have proper alignment and a balanced and blue printed prop. Wagter conditions also play a factor ie weeds. Then there can be rudder cavitation where a loose connection will cause wobble in the rudder due to offset from the propshaft to rudder angle due to bernoules principle. So. There are many causes. If your alignment is right, your prop balanced and tru , and strut bushing within tolerances then it is prob one of the above

08-28-2011, 12:36 AM
You are obviously know your way around the mechanical side of things, I am at best a weekend project guy. The rudder broke completly off. It was odd, we were towing two very large 3 person towables as we do every weekend. We made a right hand turn and the ever presistant cavitation was there then I felt a thug through the steering wheel and lost steering. Sure enough the rudder had broken off. We were in the middle of the lake in about 25 foot of water so we did not hit anything. I have been experiencing what I believe to be cavitation when turning right. The problem has been getting worse. It happens in calm water, rough water, when the boat is full ( 8-10 people) or when its just me and the wife.

08-28-2011, 10:18 AM
Since it is not normal for rudder shafts to just break, you should pull and inspect the rudder box (the thing that holds the rudder vertical insid the back of the boat). Odds are, you have a few issues.

08-28-2011, 11:11 AM
Rudders can snap from too many 45 mph U turns. The force of a 3000 lb boat on the area of the rudder can be quite substantial. Tube require 5000lb ropes and if your towing 2 large ones with 3 victims on each ,well the forces exerted on that poor little rudder may over time be overwhelming. Did you look at the rudder and strut bushing to try and find a cause of cavitation if not normal use cavitation. As mentioned by max check inside as well as alignment, strut,strut bushing slop. Depending on hours you may want to replace the 11 year old bushings anyway.

08-28-2011, 08:26 PM
Yes, on my first inboard I liked doing power turns. The result, over time, was that the rudder strut box broke. Under normal driving, everything seemed normal, but the steering got stiff at high speeds or speed with a quick turn. The box allowed water to come into the boat, but the bilge pump was taking care of most of that. I had the box re-brazed, but that didn't last long. I wound up having a machine shop make a new one out of stainless steel. No more issues.

Again, under normal driving conditions, rudders don't just break off unless there are other issues. Cypress Gardens and Sea World performed many years with MC doing power turns on every show. So, the rudder shafts are up to a lot of abuse.