How to Repair the Rudder on a Fiberglass Boat

A fiberglass boat's rudder is usually a fiberglass and foam sandwich -- at its center is a spade-shaped steel mandrel that's bolted to the boat's rudder post. Around that is a core of foam, the same foam used as flotation in the boat. The whole affair is overlaid with fiberglass. Its fiberglass surface is likely to break around the rudder post on which the rudder turns. If repairs are not made in time, water will enter the foam core.

Things You'll Need

  • Small rotary grinder
  • Automotive tire tread depth gauge
  • 80-grit sanding block
  • Automotive paste wax
  • Digital micrometer
  • Epoxy
  • 1 1/2-oz. fiberglass mat
  • 6-ounce fiberglass cloth
  • 1-inch putty knife
  • Razor knife
  • 320-grit sanding block
  • Drill
  • 1/2-inch bit
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Instructions

    • 1

      Grind away 1/2 inch of the fiberglass covering around the rudder post, using a small rotary grinder to grind through the fiberglass to the foam core. Measure the depth of the area you ground away, using an automotive tire tread depth gauge. Multiply this depth by 12. For example, if the depth of the area is 0.5 inch, the answer is 6 inches.

    • 2

      Bevel the area around the rudder post, sloping down to the rudder post, with the grinder. The diameter of the beveled area is the same as the depth divided by 12 -- 6 inches, if the depth of the area ground away is 0.5 inch. Sand the beveled surface with an 80-grit sanding block to give the repair a large grip surface.

    • 3

      Apply a thick coat of automotive paste wax around the outside of the beveled area to prevent epoxy from sticking where it shouldn't. Allow the wax to dry while you prepare the epoxy.

    • 4

      Multiply the depth of the ground-away area at the rudder post by 32, since each finished layer of fiberglass and epoxy is approximately 0.32 inch thick. For example, if the depth of the area ground-away around the rudder post is 0.5 inch, multiply 0.5 by 32. The result, 16, is the total number of layers of fiberglass cloth and fiberglass mat you will need to make the repair.

    • 5

      Measure the diameter of the rudder post, where it enters the rudder, with the micrometer. Cut circles of fiberglass cloth and mat mat the diameter of the beveled area, each with a hole the diameter of the rudder post in its center .

    • 6

      Mix epoxy resin and hardener according to the directions on the epoxy. As soon as the epoxy begins to "kick" -- that is, when it begins to thicken -- spread a coat of epoxy over the beveled area. Lay a strip of 1 1/2 ounce fiberglass mat over the epoxy and push the fiberglass into the epoxy with the blade of a 1-inch putty knife.

    • 7

      Apply a second coat of epoxy and lay a strip of 6-ounce fiberglass cloth over the second epoxy coat. Press the cloth into the epoxy and apply a third coat. Lay mat over the epoxy and push the mat in to the epoxy. Add a fourth layer of epoxy and fiberglass. Allow the epoxy to cure before adding more epoxy and fiberglass.

    • 8

      Continue adding epoxy and fiberglass, alternating between layers of fiberglass cloth and mat, taking a break between every four layers to allow the epoxy to cure, until you've built up a fiberglass covering over the repair that is as thick as the rudder's original fiberglass skin.

    • 9

      Trim the edges of the fiberglass that extend beyond the ground area, using a razor knife, and press the finished edges into the epoxy. When the epoxy has cured fully, sand the repaired area down, using a 320-grit sanding block, until it is level with the top of the rudder. Apply a coat of automotive paste wax to the repair.