How to Install Box Fins on Your Surfboard

Surfboards usually have either one or three fins. Fins help the board to glide along the surface of the water, and respond to your body movements. Fins are secured to the board's fin boxes. These boxes are sunken into the board so they are flush with its surface. Several steps are required to create a cavity in which to sink these fin boxes. Once the cavity is created, the boxes must be glued and screwed into the board.

Things You'll Need

  • Fin box
  • Ruler
  • Pencil
  • Router template
  • Router
  • Resin
  • Paintbrush
  • Squeegee
  • Screwdriver
  • Sander or sandpaper
  • Razor blade
  • 1 oz. hardener
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Instructions

    • 1

      Select the correct plug. Use the zero-degree plug to install center fins. For side fins use either the five- or nine-degree plug. Use the five-degree plug for V and standard concave bottoms, and use the nine-degree plug for boards with bottoms that are deeply concave.

    • 2

      Turn the surfboard over. Place a ruler on the backside of the board where the toe angle of the fin will be position. (See Step 14 and Tips for more information about toe and cant angles).

    • 3

      Find a location for the fin. Fins can be placed directly in the center at the tail end of the board, and at a slight angle along the sides of the tail end. Some surfboards only have one fin, while others have three; it's a matter of preference.

    • 4

      Mark two dots for the fin with a pencil to mark the fin dots. Make sure the dots are 4-1/2 inches apart. One dot must be marked where the trailing edge of the fin will sit, and the other where the lead edge of the fin should sit. Draw a line to connect these dots.

    • 5

      Position a router template over the line you drew. Make sure the rear dot is visible through the hole in the template.

    • 6

      Set a router so the depth of the cutter extends 0.63 inches, or 16 mm beyond the base of the template.

    • 7

      Hold the template firmly in place with your hand. Cut the surface area inside the template out with the router. Make sure to keep the router inside the template. Turn the router off before removing it.

    • 8

      Remove the foam from the cavity created by the router.

    • 9

      Pour a small amount of resin into the cavity created by the route, just enough to wet the entire cavity. Spread the resin along the bottom and walls of the cavity with a paintbrush.

    • 10

      Smooth a small amount of resin onto the bottom of the fin box plug.

    • 11

      Insert a dummy, or test fin into each fin box.

    • 12

      Insert the fin box with its dummy fin attached to it in the cavity. Make sure the fin box is at a proper depth; it should sit between 1/16 and 1/32 of an inch below the surface of the board. The recess is necessary to allow the fin box to bond with the foam.

    • 13

      Remove excess resin from the board with a squeegee. Allow the box fins to stay in place until the resin is dry.

    • 14

      Find the cant and toe angle of each dummy fin. These are based on personal preference. Place a fin angle template over the fin to ensure the angle, or use an angle finder tool to verify that each fin is at the toe and cant angle you prefer.

    • 15

      Remove the dummy fins from the fin box. Screw down each fin box with the included screws, and make sure the screws are deeply set.

    • 16

      Cut wax paper into shapes that are similar to the fin box. Place the shape over the fin box plugs.

    • 17

      Mix 2 oz. of resin and 1 oz. of hardener to create an epoxy. Spread the epoxy over the entire surface of the board.

    • 18

      Sand the patches on the bottom of the board to make them smooth and flush with the board surface.

    • 19

      Remove sanding debris from the fin box plugs and screw holes so the fins will have proper access to the holes. The fin boxes are now installed, and you can add the fins.