Research Notes: DIY Monofin Leading Edge

Context

The proposed monofin leading edge would use an 8 mm microporous rubber material that could be sanded into shape.

Its intended functions were to:

• protect the carbon-blade edge;
• create a smoother transition into the blade; and
• provide a replaceable, flexible leading-edge profile.

Candidate material

The specific material considered was:

• RS PRO black EPDM rubber sheet;
• RS stock number 205-428;
• 1 m × 1 m × 8 mm; and
• no adhesive backing.

The response described this as solid EPDM with a density of approximately 1.3 g/cm³ and a typical hardness of 60 Shore A. That was incorrect: the RS listing gives a density of 0.12 g/cm³, tensile strength of 0.45 MPa and elongation of 90%, suggesting an expanded or foam-like sheet rather than dense solid rubber. No Shore hardness is listed.

Product reference: https://uk.rs-online.com/web/p/rubber-sheets/0205428

The material was considered as a candidate, but the conversation did not record its purchase or a sanding test.

Proposed profile

The generated design used an asymmetric cross-section:

• rounded front;
• flatter rear transition into the blade;
• approximately 3–4 mm leading radius; and
• tapering toward 1–2 mm at the carbon transition.

The centre beneath the foot pocket was proposed as slightly blunter, with a sharper profile toward the rails. These dimensions were suggestions rather than measured or tested design choices.

Proposed construction sequence

• Cut the 8 mm EPDM strip to the leading-edge outline.
• Prepare the EPDM and carbon bonding surfaces.
• Bond the strip using SC-2000 with its specified hardener.
• Allow the bond to cure before shaping.
• Rough-shape the attached edge with 80–120 grit.
• Refine the profile with 240–400 grit.
• Keep the sanding profile consistent along the blade.
• Apply a thin SC-2000 finishing coat only as an experimental surface treatment.
• Allow the assembly to cure before evaluating it in water.

Adhesive and finish

SC-2000 with UT-R20 hardener was proposed for bonding the EPDM to the carbon. The manufacturer’s catalogue supports processing SC-2000 with 4% UT-R20, but the exact preparation and cure procedure should come from the applicable technical sheet rather than the generated timings.

The conversation also proposed using a very thin SC-2000 layer as the final outer finish. This was intended to:

• cover sanding texture;
• create a uniform black surface; and
• remain flexible with the rubber.

This coating use was generated speculation. No application or durability result was reported, and SC-2000 was not established as a manufacturer-approved hydrodynamic topcoat.

SC-BL in a 200 g package was considered as a smaller-batch alternative. REMA TIP TOP documentation confirms that SC-BL is a distinct adhesive product, but the conversation’s claim that it is simply smaller, thinner SC-2000 with identical hardener, ratio and performance was not established by the available manufacturer documentation.

SC-BL safety-sheet reference: https://surfaceprotection.rema-tiptop.com/fileadmin/data/common/downloads/safety/Files/01_German/DE_DE_TIP_TOP_CEMENT_SC-BL_0083.pdf

Inspiration

• YouTube shaping reference at 1:10:09
• AXIS Foils: Basics of Foil Design
• MDPI foil-flow profile image

These links were supplied as inspiration; their contents were not incorporated as adopted specifications.

Editorial notes and unresolved details

• The RS sheet should not be described as dense solid EPDM.
• The exact material hardness and sanding behaviour remain untested.
• The proposed foil dimensions were not derived from the linked references or validated hydrodynamically.
• Acetone, MEK, heat-gun treatment, solvent smoothing and silicone spray were generated process suggestions, not adopted steps.
• Using SC-2000 as an exposed finish remains experimental.
• SC-BL should not be treated as equivalent to SC-2000 without its technical instructions.
• No final material, adhesive, profile or finish was reported as implemented.