Flat (not wedge) rudder blade?

[lohring]

Then there's the kind of rudder for 140 mph. This picture isn't Joerg's boat, but the rudder was similar. Below are pictures of Joerg's boat. Note the shaft offset and the air rudders. The air rudders weren't for looks.

Lohring Miller

 

[tnrcboatracer]

Terry,

I think Mike was using the same Hammer knife from McM, although Lohring and Mike B have shaped it quite a bit. I tried the same hammer knife on several gas SAW boats and did not have as good results compared to kitchen knifes. I would find a good 6" to 8" pairing knife with reasonable heft and try cutting that down to fit.

TG

 

[tnrcboatracer]

Terry,

I think Mike was using the same Hammer knife from McM, although Lohring and Mike B have shaped it quite a bit. I tried the same hammer knife on several gas SAW boats and did not have as good results compared to kitchen knifes. I would find a good 6" to 8" pairing knife with reasonable heft and try cutting that down to fit.

TG

That Henkel blade is not a full wedge. The wedge break line at mid chord may be causing a flow separation that in turn causes the instability.

 

[RaceMechaniX]

I have not looked at the Henkel or other knife rudders I run that closely to notice a break in the wedge, but they do work: