The fin is a key element in windsurfing equipment, and consequently it is very handy to know how to remould a finbox. This way you can easily change the rake of a fin, shorten it to the desired length or even move it forward or backwards in the box.
What you need:
· A Tuttle finbox
· PU moulding mass
· De-moulding spray (mould release agent)
· Polyester putty
1) Making a mould:
Making a good mould is very important. You start by buying a Tuttle finbox, similar as what is used in custom and most production boards. A local shaper or repair shop is the best place to get them. Make sure you have a composite one and not the plastic version. They are not cheap, but you can share the mould and cost with some friends.
First step is to drill 2 holes, one in front and one in the back.
This will be your future reference holes. Then you cut the box in 2 parts like shown on the picture.
Since you have cut some material away, we need to build up the same amount again.
Place a fin with finbox on one side, put some thin plastic over it, and add some putty on the other side of the removed surface. Use some bolts and put the 2 halves together using the reference holes you have drilled and press everything together until the box it tight against the fin. After drying, you will notice that when placing the 2 halves together the dimensions of the box are again identical to the original box.
You need now to make a part that fills up the upper finbox hole like shown in the picture.
To make this part, you can also use the PU moulding mass. Take a fin with the finbox size you want to reproduce (depth) and put it in the mould. Then spray plenty of de-moulding spray into the opening and let it dry for some minutes. Once dry, prepare the PU and pour it into the opening. After 10 minutes, the PU will be hard and you can open the mould and get the part out for future use. If you want, you can make different parts with different heights for Deep Tuttle (formula) or normal Tuttle (slalom) fins. Important is to do a good cleaning job of your mould after each time you use it - and spray plenty of de-moulding liquid on it before every session. Your mould is ready.
2) Remoulding a fin:
Once you have prepared the mould, we need to look at the fin.
It is important to control the position of the fin in the box. Depending if you start from a cut off fin blade or an “old” box, the blocking will require some more work.
In the picture below you can see the system I’m using to fix the fin position in the box. To block it sideways, I have drilled small holes in the blade and used some screws that I use as a side stop. To fix the height position, I have taped some wooden support to the blade were I can adjust the angle and height with the aid of 2 screws.
Make sure that the mould is perfectly horizontal.
Now, take the 2 component PU, follow the mix ratio and prepare the mixture. PU is reacting very fast, so you have around 1 minute to pour everything nicely into the mould.
The PU moulding mass is very liquid and it will fill adequately every hole and gap. Use a folded and cut piece of stiff paper to pour the PU with precision into the mould.
After about 10 minutes, the PU has hardened enough so you can start to de-mould. Loosen the bolt - and thanks to the release agent, the 2 parts will separate without problems.
Take out the fin and sand off the edges slightly. If you want, you can unscrew the small side screws or if they are stainless steel, you can leave them in.
Finish the rest of the blade by drilling the finbolt holes, if needed, repaint the fin and you are done.