Research Notes: DIY Carbon Monofin BOM

After mapping out bifins, I want to gather materials and design notes for building a monofin blade. This will be a bit more complex than bifins because monofins need more lateral stability and usually use internal reinforcements.

The problems I need to solve are: 1. Which materials carry over from the bifin build 2. What extra elements a monofin blade needs (ribs, edge trims, reinforcements) 3. Typical dimensions of monofins 4. How many layers are used in commercial examples 5. How to finish the blade for durability

Core Materials¶

Most of the BOM is the same as the bifins:

Carbon cloths (200–650 g, plain weave, twill, biaxial)
Carbon ribbons (spread-tow strips for reinforcement)
EL2 epoxy laminating resin
Release agent / mould wax
Peel ply + breather + vacuum bagging film

Monofin-Specific Materials¶

Rubber U-channel trim — protects blade edges from chipping
Neoprene strips / rubber — add lateral stiffness and stabilize the blade
High-density neoprene sheet — used in some designs for damping and structural support

These help with lateral stability, which is critical in a wide monofin blade.

Sizes and Dimensions¶

Some references from commercial monofins:

Molchanovs PRO Monofin 4 (Regular): 72–74 cm length × 70 cm width
Molchanovs PRO Monofin 4 (Small): 70–72 cm length × 68 cm width
Cetma Taras Monofin: max width ~69 cm

So the range seems to be 70–74 cm wide, 68–74 cm long.

Reference article: Apneapassion on Cetma Taras dimensions

Layering¶

From examples I’ve seen:

10+ layers is common for full carbon monofins
Many use internal carbon ribs for stiffness distribution

Visual references: - Oceaner monofin layering - Cetma Taras internal structure - Bluewater Freediving ribs example

Internal and Side Reinforcements¶

Most high-end monofins use reinforcement structures:

Internal ribs: strips of carbon inside the laminate for stiffness
Strong side ribs: thicker rails or carbon laminates that act like wings, resisting side flex
Examples:
Waterway 6-rib system
Molchanovs monofin
Goldfin side ribs
Junko Kitahama competition fin

Finishing¶

Edge protection: rubber U-channel trim
Rails (optional, depending on how stable the blade feels)
Sanded and rounded blade edges for safety and durability

References I Don’t Want to Lose¶

Where I’m At¶

Compared to bifins, a DIY monofin clearly needs: - More layers (10+) for stiffness - Internal ribs to control flex and power transfer - Side reinforcements to prevent wobbling - Rubber edge trim for protection

The challenge will be building internal ribs into the laminate.
That’s probably the biggest difference compared to the simpler bifin build.

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