Install Fin Box.
I try to chose blanks with double stringers so I could place the fin box between the stringers. With the fin box, I also install oak woodies (Home
Base) on each side of stringers to further reinforce the box.
You drawn on the board with a soft yet sharp pencil.
I like mechanical pencils for doing this. The woodies I make extend at least 1½" in of front and back of the fin box and at least a ¼" inch below the fin box. An inch equals 2.54 cm.
When routing out the woodies on a thinner board the router could go through the top of tail at the rear. If this
happens shape the woody to fit the routed slot and top contour of board. Tape the fin box off.
I install one layer of 4 ounce in the woodies because the slots are tight.
The fin box layering will depend upon how wide it is between the stringers. In the past, I have used between two to six layers of 6 ounce glass. If you use more that two layers of glass check the box depth. You will not want to be grinding too much off the bottom of the box. It is better to route the box deeper to accommodate the extra glass. The more you grind off the bottom of the box the weaker the connection will be.
When I install the box, I like to use a pointer fin for better straightening reference than a wave fin. Remove the deck
taping right after it has started gelling.
Leave the fin straightening tape for at least two hours after gelling. Remove excess fiberglass with razor blade. The next day, you will carefully grind the woodies and fin box flush. As I stated before, the process I use is different from traditional methods. Most builders would have hot coated the board first. This will help keep the grindings out of the gummy laminating resin and produce a cleaner board