A run down of what happens and what I have tried from an article of foil noise
<br>1) A foil dagger board or rudder should be perfectly symmetrical.
<br>2) The trailing edge should be razor sharp in reality this is not achievable.
<br>3) The why a foil works water is split by the leading edge.The water passes over the foil at the same speed and rejoins at the trailing edge the trialing edge. This is where the noise comes from.
<br>The noise is the oscillations developed as the waters slips into the flow of water from the opposite side of the foil turbulence is caused a low pressure point is created and the water then switches across the back of the foil. the water then starts to join on the new oppersit side of the foil. A low pressure zone is now created so puling the water back across the trailing edge this happens many times a second as the low pressure skips from side to side of the trailing edge.
<br>4) to stop this noise a permanent imbalance has to be introduced. Squire the trailing edge using fine wet and dry 800 grade raped around a file should do. Make the trailing edge about 0.25 mm wide. Then with one stroke of the 800 grade bound file remove one of the corners between the trailing edge and the side of the foil.
<br>5) What happens now. The foil will split the water as before. The water will now rejoin at the trailing with the low pressure zone held in one place. The water from one side of the foil will continually slipping in a linier fashion into the flow on the opposite side.
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