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Monday, March 03, 2008

Rudder Bearing is IN!

Completed the glass-in of the rudder bearing housing this past weekend. As mentioned in a previous post, the housing is made from FR-10 tubing (thermoset epoxy) and is about 1/2 inch thick. The inside has been turned to receive the diameter of the 60mm self-aligning rudder bearing. The tube was cut to closely mate with the hull. Lateral and aft reinforcement plates made of G-10 sheet was glued to the outside of the tube and hull providing sideways and fore/aft reinforcement. All this done with an alignment rod keeping the bearing (and housing) aligned with the lower gudgeon. As this component is a critical piece (it will bear most of the side loads on the rudder), the final glass-in was done with epoxy. Epoxy provides for stronger laminates over vynilester or polyester resins. This was the first time I had done any significant lamination with epoxy (so far, most glass work has been with vynilester resin). Considering my recent post on tabbing in bulkheads (done with vynilester), I should say working with epoxy is MUCH different. Epoxy resin is generally thicker (I am using West Systems brand) therefore, it takes more work to wet-out the fabric. Apparently there are glass fabrics specifically woven for use with epoxy. It can be thinned with something like acetone, but, according to West System, strength will be proportionally compromised. Generally it went like this
  • stuff thickened epoxy (milled fibers and silica) on the inside base of the tube to fill gaps between the tube and hull, and provide a smooth fillet.
  • at the outside base of the tube, smooth out the thickened epoxy that squished through.
  • glass the tube and reinforcement plates to the hull by laying two layers of glass strips around the base of the tube and along the base of the plates.
  • fill and smooth the joints, over the recently laid glass with more thickened epoxy, such that any fillet is very shallow and barely shows.
  • Glass over the entire surface of the tube and plates with two more layers of glass, staggered, giving it a large footprint on the hull surface. Align such that the the fibers give as much "radial" coverage from the center of the tube as best you can (to provide for strength under load).
  • Once the epoxy is set, burr off any sharp edges with a grinder.
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