How to make a single fin for a longboard

Here's a step-by-step guide on how to make a homemade 10-inch single fin for a longboard or funboard.

Commercial surfboard fins are generally expensive, but the truth is that they're hard to make and require a lot of precision technology.

You can always shape it like a board maker, though it can be challenging and time-consuming.

Nevertheless, it is not an impossible mission, and above all, it's fun and can enrich your knowledge of hydrodynamics.

Don't expect to get a perfect fin on your first attempt. The more you practice, the better the outcome.

With the right tools, materials, and a bit of patience, you can create a rideable custom single fin for your longer boards.

Some of the following tools can be replaced by non-electrical hardware.

Read the do-it-yourself tutorial, follow the video, and create your first-ever surf fin.

Tools

• Mixing cups and stir sticks;
• Scissors, utility knife, or rotary cutter;
• Mask/respirator;
• Gloves;
• Rail marking gauge;
• Spiked/ribbed resin roller;
• Squeegee;
• Chisel;
• Tape;
• Sandpaper (80, 120, 220 grit);
• Wet sandpaper;
• Band saw;
• Paint filters;

Materials

• 3/16'' thick clear acrylic sheet;
• 18'' x 15'' layers of 7.5 oz plain weave fiberglass cloth;
• 50 oz polyester/epoxy laminating resin;
• 22 oz hardener;
• 5 oz resin tint pigment;
• Universal mold release;
• Acrylic gloss clear coat;
• Finishing resin (optional);

1. Lamination

1. Cut the 36 layers of fiberglass fabric using the rotary cutter;
2. Lay the acrylic sheet on a flat surface;
3. Tape the acrylic sheet off on all four sides;
4. Spray the mold release over the panel;
5. Measure out five or six ounces of epoxy, tint it, and run it through the filter;
6. Pour 20 ounces of epoxy resin into a container;
7. Add two ounces of the epoxy and tint concentrate;
8. Mix it up to distribute the color well;
9. Pour 9.5 ounces of hardener;
10. Mix it for at least two minutes;
11. Pour some epoxy directly onto the acrylic surface and disperse it around the panel using the squeegee;
12. Remove the excess;
13. Lay one sheet of fiberglass and pour more epoxy onto it;
14. Place two more layers of cloth and pour the resin, making sure it gets fully saturated and without air pockets;
15. Add two more layers and pour the epoxy;
16. Use the resin roller to smoothen and even the fiberglass out;
17. Repeat the process until you have 16 layers of fiberglass down;
18. Let it rest for six hours;
19. Pour six ounces of epoxy resin into a container and add the tint concentrate into the mix;
20. Pour your new color formula onto the nearly-cured 16 layers board;
21. Lay four clear acrylic sheets and apply the correspondent epoxy resin;
22. Let the new layers sit overnight;
23. Repeat the processes from steps 11-18;
24. Take a little bit of clear resin and squeegee that across the weave to help fill in that top layer;

2. Shaping

1. Work a chisel underneath the fiberglass board so that you can bend the acrylic and detach it;
2. Lay the board on a flat surface;
3. Mark off your fin templates;
4. Use a blade on the band saw that is appropriate for fiberglass;
5. Cut off the template;
6. Clean up the perimeter by hand with a sanding block or some sandpaper. You want a nice square perimeter so that you know that when you're shaping your fin, you're not coming out of that true shape;
7. Drill out for the pin on the back or front of the fin, depending on your template. You can use a 3/16'' x 9/16'' stainless steel spring pin;
8. Taking the base down close to the final thickness - around one inch in diameter - using a router table;
9. Start sanding the fin's starboard trailing edge using a 60-grit silicon carbide sanding pad;
10. Make even passes to try to bring out the fiberglass contour lines and work them about two-thirds of the way across the trailing edge of the fin;
11. Try to keep an even bevel and push that all the way forward, maintaining a pretty consistent width;
12. Now, take some heavily angled passes on the leading edge, leaving a little bit of margin on either side of our pencil line, wrap it around, and try to blend the leading and trailing edges together to develop a parabolic curve like an airplane wing;
13. Flip the fin and take down the trailing edge of the port side;
14. Be cautious - you don't want to blow into your base too much, but you also want to shape it enough;
15. By now, the rough shape should be looking good;

3. Sanding

1. Switch to the 120-grit silicon carbide sanding pad;
2. Starting sanding again on the starboard side, just pushing it a little further and smoothing out any of the undulations that shouldn't be there - you'll begin to see the colors come up even more;
3. Switch to the soft flex 220 grit pad and pass it around the whole surface area;
4. Take a strip of a 60-grit sanding disc that doesn't get used to round the leading edge over and spend some time there making sure that it's symmetrical and parabolic;
5. Now, work on your trailing edge to a finer taper with 120-grit sandpaper, making sure it doesn't get too sharp;
6. Continue working sandpaper on the base of the fin and all edges and surfaces using 220-grit sandpaper;
7. Make sure the base is going to fit in the fin box. Test it on a loose box, in the surfboard, or measure it using calipers;
8. Insert the stainless steel spring pin;
9. Drill a hole for the hardware using a 3/16'' drill bit;
10. Rinse the fin with fresh water to remove the dust;

4. Finishing

1. Sand the whole fin for one minute using 320-grit wet sandpaper;
2. Repeat the process with 320-grit wet sandpaper;
3. Clean the fin with denatured alcohol;
4. Spray finish it;
5. Install your custom-made surfboard fin and surf;

Words by Luís MP | Founder of SurferToday.com