Making a Wooden Longboard Fin

Recently, someone reached out to me on Instagram (@SwellSet) asking me if I could make them a wooden fin for their longboard. They had read through my other post on how I made a set of fins to repair some glass-on fins on a board I was working on and he wanted one. Having never attempted a fin that wasn’t going to be glassed on, I said sure.

Here is how I went making a DIY longboard fin:

Decide on a Template:

Being a wooden fin, you want to choose a template that suits having a stiffer material. Hatchet fins are really cool but might not be the best for this project. I settled on having a basic outline with a wider base. This would allow the fin to be thin while still having a good amount of strength.

Cut Out the Rough Outline:

After sketching out my outline onto some leftover baltic birch plywood, I grabbed my trusty $20 jig saw and went to town. This plywood gets quite a bit of chipout so I was sure to leave a good amount of meat around my outline that will be sanded down after.

Sand:

With my rough outline, I went over to my belt sander to clean it up. At this point I got the outline down to where I originally sketched it out and made sure the fin had a nice rake (curve) to it. 

Foil:

Now it was time to turn this block of wood into an actual fin. I started with the front edge and really focused on creating an even edge all up the fin. Foiling a single fin is a little more difficult than a side fin because you need to focus on getting an even foil on both sides of the edge. The best thing is to go slow and look at your progress after every stroke. 

Repeat this with the trailing edge of the fin. This is where I learned the drawbacks of using wood for this project. I was trying to get the back edge of the fin as thin as possible, but not so much that the edge would start to break off. Using this plywood, I had to be sure to leave some thickness to make sure the fin would be strong. 

Test Fit:

At this point you should test fit your fin in your box. Make sure that the tab will fit flush into the box and that there is enough space on either side of the fin to add a couple layers of fiberglass. 

Install Track Pin:

I didn't do this in my build, but when I make another fin, I will do this here. I picked up a 3/16 inch steel rod from Home Depot. I used a dremel to cut it down because the shortest length I could find was 4 ft. I then drilled a hole into the base of the fin, covered the steel in epoxy and set it in place. I let that cure and it was good to go.

Stain:

The client wanted the fin to be darker than the natural wood color, so I picked up a small container of Varathane stain in red mahogony. To get the best finish, I started with a coat of wood conditioner followed by a coat of stain. Once dried, it was ready for glassing.

Glass:

To glass the fin, I used one layer of 6 oz fiberglass (next time I’ll probably add a second layer of 4 oz for a better fit). I laid the fin out on some tin foil so I could peel it off once it cured and then I glassed the fin like normal. It has a lot of excess glass, so once the resin kicked I went out and trimmed the extra just like doing cut laps on a surfboard. 

Once fully cured, I sanded off any resin that seeped over to the other side- I had to be really careful to not sand off any stained wood. Once it was clean, I repeated the same process on the other side. 

Sand:

Now that the fin is fully glassed, I cleaned up the profile with my sander just to make sure the hot coat would go on nicely.

Hot Coat:

At this point, I hot coated the fin as I would on a normal board or repair. I did one side at a time just like when I glassed it.

Install Screw:

I then installed the fin screw (as well as the track pin but I would do that earlier next time, as mentioned above). I had to be really careful with this because this is the thinnest part of the fin and I knew I couldn’t mess up. I drilled up to 3/16 inches and test fit my screw. After, I filled the hole with resin so that the wood would be sealed. Once it cured, I re-drilled the hole so the screw would fit

Sand:

Now it was time to give the fin a final sand. I started off with 220 grit and worked my way up to polish to give it a nice shine. 

I am pretty stoked on this fin build. I learned a lot that will really help me with the next one. The fin looks good and while there is a little wiggle when the fin sits in the box, that can easily be accounted for with some tape around the base of the fin when you install it. 

Stay Stoked!