Introduction: Surfboard Single Fin

Do you want to ride a large fin longboard style, but your surfboard has the wrong fin box for longboard fins?

If so, this tutorial is for you. Today I will show you how to make your surfboard fin larger.


Old middle fin,

Fibreglass cloth,

Resin (UV cure resin, or epoxy resin with hardener),


Masking tape,


Allen wrench.

Step 1: Cut Cardboard

Draw and cut out the shape of fin you would like. Pinch the front edge of the cardboard into a streamlined shape.

Step 2: Attach to Fin

Tape the cardboard onto the existing fin.

Step 3: Lay Fibreglass on Top of Fin

I used four layers of fibreglass on each side. More fibreglass gives extra strength but also adds to the weight.

Step 4: Paint Resin Onto Fibreglass

If you are using epoxy resin then mix it with a few drops of hardener. Paint enough resin to saturate the fibreglass, so the cloth becomes transparent. Use paintbrush to push any bubbles out.

Step 5: Cure the Resin

If you are using UV resin, hold the fin in direct sunlight, or under a UV lamp, for 10 minutes.

If you are using epoxy resin, wait at least 12 hours for it to cure.

After curing, the resin should no longer feel sticky to the touch. Cut excess fibreglass away from the fin.

Step 6: Repeat Steps 3 to 5 With the Other Side of the Fin.

Step 7: Sanding

Use sandpaper to smooth the surface of the fin. I used P40 grit for the larger bumps, and then the finer P100 grit to get a smooth finish. Wear a mask to avoid breathing the dust.

Step 8: Install the New Fin

Remove the fins from your board using an allen wrench, and install the new single fin.

Hand Tools Only Challenge

Participated in the
Hand Tools Only Challenge