Article

On the water surface there are many currents which affect all surfaces of the rudder blade. As an example, we mention only one current in our article.
The movement of a catamaran on waves owing to the water flows inside the waves themselves, and causes cross pressure on the rudder blades. Crossing one wave after another, the rudders receive alternate pressures throwing together or pulling them apart. (see Fig. 1).
The pressure on rudders has a very wide range and depends on many factors (length and height of a wave, the angle of the catamaran to the wave, its speed, etc.)
Sometimes the pressure on the rudder blade exceeds 100 kg.
The catamaran helmsman does not feel them because of the crossbar, joining the rudders, and therefore the rudders can break down.

However there is an opportunity not only to avoid undesirable pressure of the force which acts on the rudder, but also to take from this an additional advantage.

Let's estimate force's quantity acting on the rudder:
At a rudder's angle deviation α°, the force R, directed perpendicularly to the rudder, is resolved into components: positive Ò - the traction force, acting along the boat movement, and force P, counterbalanced by force P ' on the rudder of the second hull.
The traction force is defined: T = R * sin α°

Let's make an estimation, the variable pressure on the rudder is about 10 kg and the deviation of the blade is 1.2 degree (Dotan rudder allows deviation of the blade 1.2 degree):

1. Additional traction force T
   
2. Decrease of the pressure between rudders and as the result it decreases
   
   • risk of rudders breakage
     
   • total water resistance on blades
   
   

Reception of additional traction force from rudders has certainly a very unexpected effect and is extremely important for racers.

How is it possible to receive traction force on the rudder?

On the basis of this idea, Dotan company has developed the rudder system of the flexible elements with a connection of the tiller with the crossbar and an elastic rudder box, which allows to use waves energy.

We tested the crossbar on special equipment in the water (waves 0.5m-3m high). This device showed us the changes in the crossbar length. The length of the crossbar changed from 10mm to 30mm, with a frequency 2-5 seconds (depending on the boats direction against the wave). All changes in the size were constant, but not irregular – one second it was smooth, one second it was like a spurt. This clearly proves that in the crossbar there are forces. During all tests none of the skippers lost control or feeling of the boat. Moreover they indicated that boat goes more smoothly through the wave.

Optimal direction.

According to the Ackerman principle, when turning on different radiuses, tillers must have particular toe-in angle. Meaning when the turn radius is large - tillers have little toe-in angle, but on sharp turns (small radius) tillers must have a larger toe-in angle. Usually sailors choose an average angle, about 7 or 8 degrees. Our system in this case automatically allows for a more optimal angle.
Usually in order to change the direction a skipper turns the rudder about 20-40 degrees. Our amortization system can only turn for 2-3 degrees, again optimizing the Ackerman principle – adding or taking the angle.
There are no slop, dead zones, delays etc… The skipper perfectly interacts with the catamaran.

Conclusion.

The article example shows how everything would work with 10kg load. If there are no wave loads between the rudders the load is very close to 0kg. When there are large waves, loads can reach about 100kg before the rudders will break.
Anyway, even with a condition when load is 10kg you can decrease drag for 0.4kg. So, you can gain about 1 minute on a finish during a 3-hour race. If you take into consideration large waves that can cause loads to reach about 100kg your final result on the finish line can be many times better.