About a year ago, my foil crashed on a log I didn't see and that delaminated my fin box. I'm finally getting to fix it and I'll post over the next few days to document how I'm doing this in case it can help someone else.

STEP 1 - Prep and removal of old finbox

Find and trace board center. measure and record where the 2 bolt holes are located on the top deck


Trace center and foilbox perimeter on board


Drill as vertical as possible the 4 corners of the box perimeter (use a square for help).


Cut through the board "skin" with a jigsaw


Locate the 4 corners of the foilbox perimeter on the opposit side of the board by locating where the drill has poked through


Repeat the jigsaw cut; on the deck side this time


Finish the cut with a Multitool from both side of the board if the jigsaw blade didn't got all the way through


Extract the old finbox


NEXT: Fit and glue the new box in place

Step 2 - Fit and glue the new box in place

Fit and clean up the cavity for a fairly tight fit so the glue has room to expand a little


Dry-fit the new box and ensure it lines up with centerline


Tape-protect deck and surfaces in preparation for glue-up


Use Gorilla Glue to glue the box in place. Make sure to recess the box by a couple of millimeters to allow for the glass or carbon layup.


Wedge wooden sticks where needed to set the foilbox in place at the correct depth and angle


Verify plumb with a fin and adjust with tape if necessary to pull the box on one side or the other


NEXT: Cutting excess foilbox on deck and sand down existing glass on both sides around foilbox perimeter

STEP 3 : Cutting excess foilbox on deck and sand down existing glass on both sides around foilbox perimeter

Hull side: Glue has cured overnight


Hull side: Clean/remove excess glue


Hull side: Tape area to protect cutout edges from sanding


Hull side: Feather-down transition around FoilBox - ready for glass. Sand further forward for carbon reinforcement.


Deck side: Glue has cured overnight


Deck side: Shave off excess FoilBox with Multitool


Sand 2mm below original deck level and feather down transition around foilbox.


NEXT: Cutting and glassing carbon layups

STEP 4A : Cutting and glassing carbon layups - hull side

Cutting carbon fabric to size - 9 layers builds about 2mm-2.5mm finished thickness


Glassing all layers and covering with release fabric (prevents the formation of amine blush, evens out last carbon layer surface, and absorbs excess epoxy)


Remove release fabric and expose carbon layup


Roughout shape surface (60), apply filler and finish-sanding (120/220/320)


Open Tuttle slot with trim router


Fine-tune slot opening with files


Test-fit both fin and foil mast



Finished Tuttle slot


NEXT : Cutting and glassing carbon layups - deck side

STEP 4B : Cutting and glassing carbon layups - deck side

Saturating foam with epoxy resin before carbon layup


Laying carbon fabric (8/9 layers) and finish with a release fabric


Shaping and initial sanding (60 grit)


Fairing coat to fill pin holes and uneven surfaces (epoxy + silica filler)


Final sanding (120/220/320) before painting. Taping for paint


NEXT : Painting top and bottom

STEP 5 : Painting top and bottom

I painted the deck black because I knew I would never be able to match the streaky effects that the original paint had. So, I decided to visually connect the black and white footstrap pads with the hope that it felt aesthetically ok and intentional


Matte black was the choice. I used Rust-Oleum Painter's Touch 2X


A couple of coats of paint and it was done! I didn't apply non-skid texture because I can't recall ever putting my foot on that area while riding. If it needs some, I could always do it later.


I also took care of giving the cutouts a coat of paint to freshen them up a bit


And went on masking the cutouts, prepped the surface sanding with 320, and was ready for a couple of coats of white


Luckily, the Rust-Oleum white is almost a perfect match to the original Fanatic white. Makes it easy to blend into the existing paint


Paint is done! I wet-sanded between coats with 400grit dry/wet.


I masked a margin around the Tuttle slot: This is to avoid having paint chipping on the edges of the slot when installing and removing fins. Chipping existing finish happened to me before


A nice and flat transition should guaranty the same performance as the original. I also wet-sanded the finish to satin with 800 wet/dry sandpaper. I finished the sanding with strokes running longitudinally to the board.


NEXT : Drilling the screw holes

STEP 6 : Drilling the screw holes

For accuracy, I needed to build a small jig so the holes would be positioned exactly where intended. I did it by:

• Cutting and gluing 3 layers of thin plywood scraps that were laying around in my garage
• Laying out the jig outline with a printed to-scale dimensional drawing of a Deep Tuttle head
• Gluing the print to the 3 layers of ply, stacked and double-sided tapped, and cut to size at the chop-saw
• Dividing/cutting the center layer into 3 segments, removing the equivalent of the plywood thickness centered on the axis of each Tuttle fin screw in order to form 2 channels that I can later drill through
• Gluing with carpenter's glue and clamping the plywood layers together
• Increased the diameter of the 2 channels with a few drill bits of increased sizes. I tried to make sure the hole was not drifting off-center while drilling. This is to at least fit an M6 screw
• Chamfering all short edges to accommodate the Tuttle slot corner radiuses
• Attaching a scrap piece of ply on the surface where the fin would normally be in order to level the jig flush to the edges of the Tuttle slot before drilling through the board.
• Labeling the front of the jig as drilling in reverse would be very upsetting!



Time to drill the holes. For now, I just drilled to accommodate M6 screws. I'll enlarge the holes for an M10 once I receive the long Titanium 90mm M10 I ordered to fit my foil.


That's the finished result. Holes are positioned perfectly and the fit is accurate.


I hope this might help some to tackle a foilbox refit on an old board to get started windfoiling. There's nothing really difficult here. It just takes time between steps for the resin to cure. My advice: To get an even finished surface without bumps, valleys, or excess material cresting over the surrounding surfaces, I recommend frequently passing your hand over the area being faired so you can feel the unevenness. I would also use sanders and other tools with a light touch and frequently check your work so you don't have to dig into the glass layers deeper than necessary. Post below or contact me if any questions.

Bravo, kudos, amazing.....
I learned a lot, but I am amazed or surprised that what is supporting a fin box, is basically carbon/fiberglass bonded to the top/bottom layers of board... on the other hand, what else is there? How much actual labor time (not including waiting to dry time) was involved? How does a dedicated foil box differ from a standard deep tuttle box? Do you think a standard deep tuttle box (eg my Bic Nova 165) can support a foil under normal use (eg not running to logs) or would something like Windance power plate be advisable?

David Mark wrote:
Hi David. Thanks!
• Yep, top and bottom glass make for a big portion of the structural integrity. The glue or resin used to bond the box to the eps foam is also not a negligible factor to provide strength.
• Time-wise, I didn't really count but I think I spent between 7 and 8 hours total. I probably wasted time contemplating my work with a beer in hand more than necessary! If I had to do it again, It would probably take me 2/3 or 1/2 that time.
• A std Deep Tuttle will work with a foil (That's what was in my board before) but it doesn't have enough reinforcements on the hull forward of the slot box (lots of pressure due to the foil there) and Std Deep Tuttle box are ~2" wide while foil-ready boxes are 4' to 4.5". This is for lateral strength.
• I successfully used the Powerplate on that board with my foil prior to running into a log. The device just adds a bit more weight to the kit and obviously isn't smooth under the hull. Not sure if that changes much of your ability to take off early or not. It probably just creates a bit more drag until you're up and foiling.

If you are thinking of buying a PowerPlate, I can sell you mine for a good price. I don't need it anymore! PM me if you're interested.