Long Fins - V2 - Stiff Competition¶
Full-length competition fins tuned to the stiffer side for a stronger kick response. This v2 keeps the v1 process and geometry, while targeting a 90-degree bend load in the 1.8-2.0 kg range.
Planning¶
Foot pockets ready¶
Make sure your foot pockets are on hand before you start. If you still need to choose a pair, follow the steps in Choosing the foot pockets. Once the pockets are sorted, lay out a fresh cutting template with Laminated paper cutting template.
Heads-up: The dimensions below assume 170 mm of blade will slide into the foot pocket. Measure your pockets to confirm before cutting.
Specifications / Dimensions¶
Target outline for each blade:
- Width: 18 cm
- Total length: 17 cm + 58 cm = 75 cm
- 0–17 cm: inside the foot pocket (flat section)
- 17–75 cm: free blade to the trailing edge
Layer schedule (one blade)¶
For this build I am going to be using a triangles to smooth the transition between the various thickness levels.
- Reserve 17 cm from the heel line for the bend zone.
- Layer 1: 20 cm × 80 cm
- Layer 2a: 20 cm × 80 cm half triangle
- Layer 2b: 20 cm × 80 cm the other half triangle
- Layer 3: 20 cm x 80(-35) ^ mid shape triangle
- Layer 4: 20 cm x 75(-15) V side shape
- Layer 5: 20 cm x 55(-10) V side shape
- Layer 6: 20 cm x 45(-10) V side shape
- Layer 7: 20 cm × 80 cm top ply
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|---|---|
| Expanded Laminate View | Laminate Thickness Profile |
Cutting plan¶
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|---|---|---|---|
| Cutting plan for first blade | Cutting plan for second blade (identical) |
Estimating the flex¶
Start with the Flex predictor modelling workflow to sanity-check the layup. Adjust the layer stack and bend allowance until the predicted deflection matches your training goal.
Free blade length [mm]: 580 Blade width [mm]: 180 Layers at foot: 7 Layers at tip: 3 Min layer length [mm]: 150
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|---|---|
| Bending Calculation | Bending Profile |
Predicted:
- Load required for 90° = 18.6 N (1.90 kg) (provisional)
- Hydrodynamic resistance score 5N = TODO
- Hydrodynamic resistance score 10N = TODO
The predicted code for this fin would be (see hydrodynamic resistance codes):
TODO
Reference images¶
TODO after build.
Time needed¶
| Technique | Implementation | Waiting |
|---|---|---|
| Foot pockets Choosing the foot pockets |
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| Base Support Creating a laminating base |
0.75 h | 0 h |
| Laminating Carbon Creating the carbon laminate ×6 |
1.5 h | 12 h |
| Vacuum Bagging Reducing the resin percentage of the laminate |
0.25 h | 0 h |
| Cutting Cured Carbon Producing the final shape |
1 h | 0 h |
| Finishing Carbon Finishing the carbon laminate surface |
0.1 h | 24 h |
| Gluing Fin Rails Gluing Fin Rails |
0.5 h | 12 h |
| Total | 4.1 h | 48 h |
Bill of Materials¶
| Technique | Material | Quantity | Unit Cost | Line Cost |
|---|---|---|---|---|
| Foot pockets Choosing the foot pockets |
Bifin Footpockets Reusable Pair of angled freediving pockets with short rails |
1 pair | £36.00 - £58.00 per pair (recorded range) | |
| Foot pockets total | £36.00 - £58.00 | |||
| Base Support Creating a laminating base |
Acrylic sheet (A3, 2 mm) Reusable Six panels for laminating base |
1 6 pack A3 sheet (2 mm) | £16.00 per 6 pack A3 sheet (2 mm) | £16.00 |
| Plywood sheets (300 × 200 × 1.5 mm) Reusable Pack of thin plywood sheets for wedges |
1 Pack of 8 sheets (300 × 200 × 1.5 mm) | £8.48 per Pack of 8 sheets (300 × 200 × 1.5 mm) | £8.48 | |
| Plastic corner braces Reusable 90° braces to lock triangles into a wedge |
1 Pack of plastic 90° corner braces | £4.89 per Pack of plastic 90° corner braces | £4.89 | |
| Super glue Consumable Fast-set cyanoacrylate for bonding braces to plywood |
1 3-5 g tube | per 3-5 g tube — Inexpensive | ||
| Cello tape roll Consumable Clear tape to tack the wedge to the acrylic or bench |
1 roll | Inexpensive | ||
| Electrical tape roll Consumable Wide PVC tape to join acrylic seams |
1 roll | Inexpensive | ||
| Base Support total | £29.37 | |||
| Laminating Carbon Creating the carbon laminate |
Carbon Fiber Fabric Consumable 0.3 m² of 200 g/m² 3K 2/2 twill cloth |
1.8 m² (1 m wide) scaled ×6 — base 0.3 m² (1 m wide) |
£17.00 per m² (1 m wide) | £30.60 |
| Laminating Epoxy System Consumable 150 g mixed resin (approx. 150 ml) |
1.5 500 ml kit scaled ×6 — base 0.25 500 ml kit |
£15.00 per 500 ml kit | £22.50 | |
| Pva Release Agent Consumable Two thin coats on the laminating base |
1.05 200 ml bottle scaled ×6 — base 35 ml (two thin coats) |
£5.00 per 200 ml bottle | £5.25 | |
| Peel Ply Consumable Two layers cut to the blade outline |
0.6 5 m pack (1.5 m wide) scaled ×6 — base 0.6 m (1.5 m wide) |
£12.00 per 5 m pack (1.5 m wide) | £7.20 | |
| Consumables pack Consumable Gloves, mixing sticks, acetone wipes |
6 pack scaled ×6 — base 1 pack |
£1.00 | £6.00 | |
| Laminating Carbon total | £71.55 | |||
| Vacuum Bagging Reducing the resin percentage of the laminate |
Vacuum Bagging Kit Reusable Heavy-duty storage bag plus compatible hand pump |
1 kit | £9.00 per kit | £9.00 |
| Breather Cloth Consumable Wraps part to distribute airflow |
0.5 m (1 m wide) | £12.00 per 5 m pack (1 m wide) | £1.20 | |
| Vacuum Bagging total | £10.20 | |||
| Finishing Carbon Finishing the carbon laminate surface |
Clear Coat Spray Consumable Two light passes for sealing and gloss |
0.2 400 ml can | £8.00 per 400 ml can | £1.60 |
| Acrylic Car Paint Consumable Single colour coat between clear layers |
0.25 400 ml can | £8.79 per 400 ml can | £2.20 | |
| Printable vinyl decal sheet (optional) Consumable Gloss white adhesive sheet for logos Optional branding layer |
1 sheet | £1.50 | £1.50 | |
| Finishing Carbon total | £5.30 | |||
| Gluing Fin Rails Gluing Fin Rails |
Rubber Fin Rails Consumable One pair of soft rubber rails sized for bifin blades |
2 m (enough for four rails) | £6.00 per metre | £12.00 |
| Plastic To Carbon Adhesive Consumable 25 ml of 3M DP420 mixed with nozzle |
1 25 ml syringe | £8.25 per 25 ml syringe | £8.25 | |
| Super Glue Consumable Thin cyanoacrylate to wick into any tiny gaps after bonding |
1 3-5 g tube | per 3-5 g tube — Inexpensive | ||
| Fold-back clips set Consumable 20 mm binder clips for clamping rails during cure |
1 set | Inexpensive | ||
| Gluing Fin Rails total | £20.25 | |||
| Consumables subtotal £98.30 | + | Reusable subtotal £74.37 - £96.37 | = | Grand total £172.67 - £194.67 |
Tools Required¶
| Tool | Techniques | Purpose |
|---|---|---|
| Brushes | Laminating Carbon | Apply resin and coatings evenly across the laminate |
| Craft knife | Base Support | Cut plywood triangles and trim edges |
| Digital scale | Laminating Carbon | Weigh resin batches for accurate mix ratios |
| Dust mask | Cutting Cured Carbon | Prevent inhalation of carbon dust during cutting |
| Dust mask or respirator | Finishing Carbon | Avoid inhaling paint mist |
| Fine-tip applicator (optional) | Gluing Fin Rails | Control super glue wicking along the rail seam |
| Gloves | Laminating Carbon Cutting Cured Carbon Finishing Carbon Gluing Fin Rails |
Protect your hands from resin, adhesives, and carbon fibers Protect your hands from paints and solvents |
| Junior hacksaw with a fine-tooth metal blade | Cutting Cured Carbon | Cut the cured carbon cleanly without fraying |
| Lint-free cloth | Finishing Carbon | Wipe dust and fingerprints before spraying |
| Metal file | Vacuum Bagging Cutting Cured Carbon |
Smooth cut edges and remove burrs |
| Mixing pots | Laminating Carbon | Measure and combine resin and hardener accurately |
| Mixing sticks | Laminating Carbon | Blend resin and hardener thoroughly |
| Plastic finned roller (75 mm) | Laminating Carbon | Consolidate layers and push out trapped air |
| Protractor or angle finder | Base Support | Mark 27° triangles and confirm wedge angle |
| Safety goggles | Cutting Cured Carbon Finishing Carbon |
Protect your eyes from dust and splashes Protect your eyes from overspray |
| Sandpaper | Gluing Fin Rails | Prepare and smooth surfaces for better adhesion and finish |
| Scissors | Laminating Carbon Vacuum Bagging |
Cut materials like fabric, film, or templates to size |
| Tape measure | Base Support | Check dimensions and spacing during setup |
| Window cleaner | Gluing Fin Rails | Degrease surfaces before bonding or sealing |
Instructions¶
- Build a 1000 mm × 600 mm laminating base following Creating a laminating base so both blades can be laminated at the same time.
- Lay up the carbon according to the schedule above, using the steps in Manual wet layup stack.
- Pull the stack under vacuum to tighten the fiber volume, referencing Enclosed bagging.
- Trim the cured laminate to the template with the Junior hacksaw method.
- Seal the surface with the approach in Clear coat and acrylic paint.
- Bond the rails using the guidance in Two-part adhesive plus super glue.
Results¶
Desired vs Predicted vs Actual¶
Record the flex after fabrication using the Kitchen Scale Test.
| Desired | Predicted | Actual | Notes | |
|---|---|---|---|---|
| Free blade size | 580mm | 580mm | TODO | Copied from v1 baseline geometry |
| Blade width | 180mm | 180mm | TODO | Copied from v1 baseline geometry |
| Load for 90 degrees | 1.8-2.0kg | 1.90kg (provisional) | TODO | Validate after first flex test |
Water trial¶
TODO after build.
| Desired | Actual | Notes | |
|---|---|---|---|
| Hydro resistance 5N | TODO | TODO | Measure after first water trial |
| Hydro resistance 10N | TODO | TODO | Measure after first water trial |
Final code after build and testing (see hydrodynamic resistance codes):
TODO