Windsurfing/SUP Board

Overview

During late May and early June 2025 I fabricated a windsurfing and SUP board with a mast box. The core is EPS foam, shaped with a hot wire and wrapped in two layers of 3K carbon fiber and marine-grade structural epoxy.

The layup, the cutter’s power supply, and an infused fin each failed in a specific way. The board works. The fin on it is a pre-built plastic injection-molded part. It was a good lesson in composite manufacturing.

Role

I owned the build: the hot-wire cutter and how it was powered, the foam shape, the carbon and epoxy layup, the mast box, and the decision to drop the infused fin.

The deliverable is the board, plus a record of why the fin attempt did not hold. There was no team title on this one.

Approach

• Glue the EPS blanks and shape the plug with a custom hot-wire cutter, including the mast-box pocket.
• Lay up two layers of 3K carbon with marine-grade structural epoxy over the core, then clean up the surface.
• Try a lightweight composite fin with resin infusion in 3D-printed molds.
• Fit a pre-built plastic injection-molded fin after the infused part would not hold rigidity.

Outcomes

• A functional board: EPS core, mast box, and two layers of 3K carbon and marine structural epoxy, built in late May and early June 2025.
• Creases in the carbon, and no tape on the underside, left sharp fiber strands that had to be post-processed.
• The hot-wire power supply blew repeatedly because Nichrome current was not regulated. A new supply and short cuts finished the shape. A CNC router would have made the plug less painful.
• The infused fin failed: resin voids, the layup schedule, surface finish, and trouble with consumables. The 3D-printed molds were relatively smooth, but tiny voids on them left a fin that lacked rigidity.
• I used a pre-built plastic injection-molded fin instead.