I'm good in negative stuff so let me give everybody the sceptic view on it.

-1- How many times are the wave lengths on the watersurface about the width of the catamaran ?

This situation gives the max "bad" effect as the article claims. Of course the little eddies as depicted in the waves are proportional to the wave height and speed of travel. If my memory about this subject doesn't fail me. In my experience; wave with a wavelength of only 2.5 mtr are both small and slow therefor I feel the eddies in them are relatively small.

-2- A flexible rudder stock like that or even a flexible tiller will result in less direct steerage and possibly even in some jawing effects. Almost like steering a car with slop in the steering wheel. Remember the difference in feel between powersteering and unpowered steering. You could steer the car by your fingertips in the latter case while powersteering setups tend to have a small delay or deadzone in the steering action ?

-3- Want to loose 0.4 kg in drag on a total drag in the order of 30 to 50 kg's = 1.33 - 0.8 % => 0.6 - 0.4 % speed increase theoretically or on avarege 18 second per hours when everything is as they say.

-4- As far as I know these eddies occure near to the surface and not at depth. So it is quite possible that the upperhalve of the rudder blade experiences these while the lower halve is in "stationary" water. We may be overestimating the magnitude of the effect.

-5- With a catamaran at speed passing waves how will this system work. Will the rudder blade move continiously from side to side. Being a rotational action in stead of a translating actions this means that a large portion of the rudderblades is not perfectlt aligned with these eddies and therefor creates all kinds of turbulance. Ergo does the added drag not outweight or cancel out the positive effects.

Wouter