I started by taking careful measurements of the old rudder. I measured how much room under the aft bunk and extended the shaft 2" to accommodate the autopilot and emergency tiller. Also I made the prop cutout 2" larger for the feathering prop. The old rudder was within a 1/4" of the prop.

 

On the build I started with a one piece shaft 1-1/2" diameter x 6' shaft alloy 17 for $216. The flats and pintle were machined and the shaft and cut to length (machining extra). Cut out the U plates out of 1/4" 304 with a plasma cutter. The spacers are from 1/4 x 1-1/4" 304 flat bar. I did as much welding as possible before welding the armature to the shaft. Everything was welded inside and out with 316L rod. The square plates are from 1/16" 316L but 304 would of been just as good. Be sure to align the plates to the flats (mine are 45 and 135 degrees) in the shaft so your quadrant and rudder will align.

 

The foam is 1/2" 3 lb Divinycell PVC foam. Very expensive at $250 for 2 sheets plus $115 for shipping the 100 miles to my boat. I could have used extruded polystyrene (the pink stuff) from Home Depot for $15 a sheet, but it is not as strong or water resistant as the PVC foam. Polyester resin will melt polystyrene but not Divinycell. I used West Systems epoxy resin. If you use polyester resin use the no-wax. It will remain tacky for most of the day and you can then lay up more fiberglass without sanding. I passivated the stainless steel with oxalic acid then coated all of it with West System epoxy.

 

I then sandwiched in the foam sheets and epoxied. I built up the foam to more than 4" around the shaft with 1/2" sheets. I then began shaping the foam. I profiled the old rudder using an outside caliper (acually it was just a large clamp) and bevel gauge. Next I planed the foam using a hand held electric planer. I first tried using a hot wire cutter but could not get any sort of precision. Plus it was hard to cut through the epoxy. Then I tried a cheese grater and long sanding block, much better but it would of taked me days. I was able to get the profile I wanted in under two hours with the electric planer. When finished shaping the foam I allowed 1/2" under the finished rudder thickness of 4". This was so I could lay 1/4" of fiberglass all around.

 

My old rudder measured 4-1/4" thick around the shaft. It scraped the skeg. I layed up 1 layer of 10 oz. fiberglass cloth and then filled all voids with epoxy. Only pour small amounts of epoxy at a time. A thick pour will get very hot and melt the foam. The last step was adding 6 more layers of 10 oz cloth and one of heavy roving. After a final fit check I cut the shaft out where the prop cutout is and fiberglassed over the ends of the shaft, building up to 1/4" of fiberglass. Any small voids or valleys I filled with epoxy thickened to a thixotropic (non-sag) state with Cab-O-Sil. (In my opinion the Cab-O-Sil is just as good as any of the West Systems fillers and much cheaper at $7.50 for 5 lbs.)

 

With the final layer of fiberglass I added West Systems Barrier coat and white pigment. The barrier coat makes the epoxy a dark grey but with the white pigment it came out a very light grey. Note adding the barrier coat powder made the epoxy thicker and a little more difficult to use. Plus it seemed to shorten the pot life. After achieving the shape I wanted I the washed off the amine blush with plenty of water and Purple Power. If I'd used polyester resin I would not of had to do that. Then I applied 3 thin coats of white Gel-Coat using a foam roller. Caution: use the good white ones; foam brushes and the yellow rollers will disintegrate almost immediately.