Catamaran Sailing
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Eliminating Rudder or Dagger Board Hum

Does your cat talk to you?  When you are screaming on a reach do the rudders screech or hum?  Some rudders sing, others screech, and yet others seem to howl.   There are actually some people that like it.  They say "that way I know I'm going fast."  If you are not one of those, here is a way to get rid of the hum.

Many people know that they should do something with the trailing edge to get rid of the hum.  There is a Hobie product designed to shape the trailing edge (product #82401000).  It is a bar with a V-shaped grove.  You just drag it across the rudder and it shaves the correct shape to remove the hum.  I hear it is a great tool and works well, but at about $25, it is a little pricey unless you are going to do several boats.

Other people say you can do the same thing with scissors.  Just open them up and drag them across the trailing edge.  The only problem is, at what angle do you open the scissors?

To answer that, we have to get some help from our mono hull friends.  Yes, mono hulls go fast enough to have the same problem.  Below is a tech tip for a J/24.   It is written by Geoff Moore of Shore Sails.

http://sailing.org/j24/tips/humm.htm

I applied his tips to my singing H16 rudders.  Using a fine file, I freshened up the edge trailing angles, making one of them longer (hence a different angle).  Then I made a 1/16" squared off trailing edge.  In one rudder tuning session the singing was gone.

Here is a drawing of the newly shaped trailing edge