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Research Notes: DIY Carbon Bifin BOM

Now that I’ve mapped out the foot pockets, I want to gather everything I need for actually building a short carbon bifin blade. This is basically my BOM (bill of materials) plus a few notes on layering and finishing.

The problems I need to solve here are: 1. Which carbon fabrics and resin to use 2. How to prepare and laminate properly 3. What to use as a support base 4. How many layers are typical for bifins 5. How to finish the blades with rails and glue

Core Materials

Carbon cloths (from Easy Composites): - 210 g 3k plain weave - 200 g 3k plain weave (same as above) - 200 g 3k green twill — decorative option - 650 g 12k twill — heavy, budget-friendly stiffness - 450 g 12k twill - 300 g 3k biaxial ±45° — for torsional strength

Carbon ribbons: - 80 g spread-tow ribbon, 15 mm — useful for reinforcement strips along rails or centerline.

Epoxy resin: - EL2 Epoxy Laminating Resin

Prep and Vacuum

Support Base

I’ll need a flat sheet to laminate against:

I still need to test which one works best. Acrylic scratches, polycarbonate might flex, but both should be fine for smaller training fins.

Layering and Sizes

From the references I found:

  • Leaderfins → 7–8 layers, blade size ~24 cm × 54 cm
  • C4 → 7 layers, but much longer (around 90 cm)
  • DIY YouTube builds → around 6 layers

For a short training bifin, I’m probably aiming at 6–7 layers, depending on stiffness.

Reference image: Leaderfins carbon stereofins

Finishing

Rails: - Waterway fin rails kit - Rail glues mentioned: Loctite 480 or 3M Marine 5200 - Good reading on rails: Spearfishing World thread

The rails help channel water and also protect the blade edge.

References I Don’t Want to Lose

Where I’m At

For a short carbon training bifin, I’ll probably go with: - ~6–7 layers of 200 g 3k fabric, maybe mixing in a heavier layer (450–650 g) for stiffness - EL2 epoxy resin - Laminating on an acrylic/polycarbonate sheet - Adding rails with Loctite 480 after trimming

This should give me a small, stiff blade that can take some abuse during training without overcomplicating the build.

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