Friday, August 24, 2012

Rudder attachment

I fabricated the rudder cassette this week.  For those who are not familiar, the cassette allows the use of a simple rudder foil which is inserted into from the top.  This allows the sailor to raise the rudder in shallower water and still have some steering.  It also makes it easy to remove the rudder foil when pulling the boat onto a trailer.

I fabricated the cassette using the rudder foil as a mold.  The first step was to wrap the finished rudder in 6 mill plastic with a couple of wraps to provide decent clearance between the cassette and the foil.  I then used the same CF sleeving that I used to create the rudder foil for the inside and outside layers of the cassette, with layers of uni-directional carbon fiber in the middle layers.  Once the epoxy set, I then glued on some "stand-offs" to hold some G10 (fiberglass) tubing in front of the leading edge of the rudder cassette.  The tubing has a 3/8" inside diameter and is intended to hold the stainless steel pin.  Once the epoxy was dry, I faired the area around the tube to insure a nice smooth finish and then wrapped 4" wide unidirectional strips of CF around the G10 tube.  One point is that I used a single length of tubing along the leading edge of the cassette so that I didn't have to worry about aligning different sections of tube.  I later cut off the tube sections that I didn't want.  The picture above shows the cassette before I trimmed it to length.  It also shows the "handle" which will attache to the tiller.  The handle was fabricated using a piece of ordinary pink insulating foam from Home Depot.  I turned the foam on a lathe to get the shape that I wanted (a slight taper from back to front).  I then wrapped the foam with release cloth, then layers of CF (sleeves and uni) and then wrapped that in release cloth.  Once everything hardened, I removed most of the foam using a 1" hole spade (flat drill bit).  Using some needle-nosed pliers I took out the inside layer of release cloth, by just grabbing a corner of the cloth and twisting.  After taking off the outside layer of release cloth and then cutting a U-shaped channel in the handle, I then epoxied it onto the cassette.  I did drill a hole from the top of the handle to allow the rudder pin to be inserted from the top.

 The picture to the right shows the cassette mounted to the stern of the boat with the handle attached to four heavy duty gudgeons (the stainless steel straps which hold the rudder pins) from Racelite hardware.
There have been some broken rudders on some of the earlier i550 boats.  Some of these failures were due to the rudder attachment points bending.  With the four gudgeons and a single 3/8" stainless steel pin, I'm confident that these won't be a point of failure (hopefully the cassette or the rudder foil itself are up to the task)

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