You were right decrepit, it got technical. I cut the recesses out with a knife, but I could not penetrate the glass layer over the recesses, and I didn't want to go too hard incase the layer lifted off the box. So I used a Dremel router. Big mistake. It made the fibre unbond right to the edge of the recess. So, I filled up the recesses with 1mm of epoxy (that will make the fastening surface flat), and tried the same procedure on the walls of the recesses more small strips of glass... which failed. I scrapped them off. I packed up the top of box with a few layers of glass.
Worse case scenario, if I am not happy with recesses, I'll fill them up with epoxy and route nice neat round holes.
Ok , this is what I would now do . Don't panic . Take off the tape and sand the glassed area . Then as you said fill the recesses . Finely chop some fibreglass. A quarter cup flufffed up . Make a small batch of resin and add the glass fibre fluff until it's as thick as jam . Stuff it into the recesses and poke at it to remove as much air bubbles as possible . I would do it in two stages , no more than 5 mm thick at a time so it doesn't get too hot . Over fill the recesses . Sand the filled recesses area to blend in . Cover the whole fin box area with one more layer of glass . Sand area . Bog . Sand again . Drill the screw holes from the bottom , fin side , out through the top of the board . 7mm drill . Then re rout a smaller , shallower recess than you originally had . That should make it solid . Lightly sand and paint .
Hi Imax. So what you're implying, is if I fill the front recess with epoxy, it will go into thermal runway and melt my fin box ?
Ok, no worries, I'll do that.
Select to expand quotejn1 said..
Hi Imax. So what you're implying, is if I fill the front recess with epoxy, it will go into thermal runway and melt my fin box ?
Ok, no worries, I'll do that.
It could go into thermal nuclear meltdown disrupting the space time continuum .
That would be bad .
Select to expand quotejn1 said..
You were right decrepit, it got technical. I cut the recesses out with a knife, but I could not penetrate the glass layer over the recesses, and I didn't want to go too hard incase the layer lifted off the box. So I used a Dremel router...
You have reminded me of why a vacuum bag is important. You are game doing these sorts of repairs without one 
LOL Ok Imax. I'll follow your guidance exactly as you said above.
Nb/ I looked up the details of the Aparency epoxy I am using. They recommend curing depth of no more than 10mm to avoid heating. The fwd recess is 30x25x10mm.
Regarding the forward recess depth, I based that by getting one of my tuttle long screws with the nylon washer + steel washer and turning it up side down and putting it in to the recess to test it's depth. Then cutting a bit more out of the recess, and retesting it's depth with the fastener. I based the depth that the fastener just sticks out of the recess with the bog on. So when the padding goes on, the bolt is (hopefully) flush with the deck. I don't want my foot touching the bolt. I know it will bug me !. So, I would like to keep the recess approx 10mm deep.
FN: Ok. Thanks. Does the vacuum bag technique improve conformity alone ?, or does it do other stuff as well ?
If anything, this thread is an illustrated 'how not to do it' example 
. Anyway, it's all learning for me.
Select to expand quotejn1 said..
FN: Ok. Thanks. Does the vacuum bag technique improve conformity alone ?, or does it do other stuff as well ?
.
Yeah, it just means that when you do things like the recesses it pulls the glass down into the void and follows the countours of whatever is there. It bonds things more easily as it forces it into contact whereas without it you have to use more resin or use some other method of holding it in place.
It's not perfect and at least for me requires a lot more pre-work, but it generally makes things easier when its setup properly. I have had times when the bag has vacuumed down perfectly and other times where I couldn't find leaks in the bag and the bag would not draw down properly.
Latest update. I was very ill for a week (and I'm still not right), so did nothing in that period. I was able to pick up the tools at the start of the week:
As recommended by Imax, chopped up glass fibre, and mixed with epoxy to make a jammy paste.
I did this is two stages as recommended by Imax. The result.
Bog sand, bog sand, bog sand, bog sand... and if in doubt, bog sand again... really built it up over a period of 5 nights.
Now to drill the holes for the fin screws (going in from the bottom of the fin box).
With fin in and the screws fastened, all looks good. No wonky holes. Pfew !
Next, plane out the wells so that the bolts have a flat land to mate against.
Donesky. The rear well was really hard to see when I was routing it. Not a perfect job I wanted, but oh well.
Although, on the front well, I did manage to route through to the filler again. So, fixing that now. I'll reroute this well out tomorrow. Didn't bother with the jam this time. Just straight epoxy. I only want a seal.
Hilarious thread; mate, I admire your patience, especially when things went TU a couple of times.
You just went at it again. Great stuff.
Hope to hear you happily wanging (that's a technical term for planing) across the water on it sometime soon.
cheers
k.
This morning's effort. The fin bolt wells are wonderful now
New problem. When fin is fastened and bolts done up, the fin is recessed in the box by 1.5 to 1.7 mm. Should I sand off the bog and live with an exposed fin box ?. If I leave it how it is, then this probably does not matter, as this is not a performance board. But it would be nice to have fin flush with board for aesthetics.
PS/ Yes, those bolts are the security type. Stainless 304 in M6 x 100mm. That's all they had at Bunnies. I'll see if I can order some Philips bolts online.
www.bunnings.com.au/pinnacle-m6-x-100mm-stainless-steel-security-bolts-4-pack_p2421016
Absolutely leave the glass over the box. Thats where all your strength is. If you took the glass off, it would only drop down 1mm or so. It looks like it's a bit of a loose fin. The other fin you used to check squareness looks fine. How does this fin fit in other boxes? If it's a bit loose, it's easy to make the fin bigger so it doesn't go down as far. We're not talking much. After sanding the ends of the fin head, paint a layer of resin over each end. Lightly sand and check for fit. By the look of the amount of sink in the pic, I layer of resin each end should do.
Ok.
I checked all my fins (noting all my fins fit fine on my other boards- Falcon, Patrik slalom). The only fin that fits ok is my MUF slalom 22 (which is a fin I would not use in this board). But even then, this fin's base is recessed as well. The problem is, if I mod my fins to fit in the Supersport, they will no longer fit into my other boards.
Having a think about it, what I should have done when I was sanding back the box (back on the 10 November), I should have tested the cut depth with a fin to make sure I had cut off 1.5mm (instead of using the 1.5cm estimate). Then, when I glassed over and sanded, it would have been perfect. I therefore did not sand off enough surface.
Slowy says fins under by a mm or so is ok, you just don't want them above. I have a fin that's a bit under on my speed board, doesn't seem to matter.
Ok, no worries. I'll just leave it.
The top is done.
I go into Auto One and ask for "car paint that sticks to anything, dries quick, and doesn't have acid in it... It's for a surf board". Sold:
A quick "shhh, shhh, shhh".
The new pads. I used the old pads as a template.
So, that's the top done.
Ok, I'll flip the board over now and give the bottom a quick spray and we'll call it done.
(I'll be back in 5 min )
The Finale !
That primer filler is excellent. It has a rough finish when I rub my hand over it. It feels like wet n dry.
The result (yes, the tape will be removed once the decking contact adhesive is cured - the can says overnight):
But, as Jem Hall once said: "The proof is in the eating". So, I'll see how it goes on the water. Today would have been good. 15 knots. This would have been the board to use.
Imax: Instead of painting the fin with resin and building it up, could I do that with the ends of the fin box ?.. or "Leave it Jason !"
You can't really build up a plastic box . Nothing will stick to it . I'd say your job is done . Ride it like you stole it . Job well done
Hi,
just a quick one: Now that you are a pro in modern composites: Just make a g10 spacer for your fin that goes on top, so that the fin sits flush. We have done that for foils in the past and that worked out fine. You can glue it with the same stuff that you glue your footpads, that way it goes off easy when you need the fin for a different board. Or glue it in the box with contact glue. It will probably never come off again :-).
David
Select to expand quotejn1 said..
Ok. That's David. Good tip
Hello J, Its your sailing buddy here with the windsurfing tip of the day.
This fin being too low in the board has been a problem for me until I started dropping a rubber band in one end of the taper.
Sometimes 2 rubber bands is needed. It works a treat and a box of them costs almost nothing.
Select to expand quotesputnik said..jn1 said..
Ok. That's David. Good tip
Hello J, Its your sailing buddy here with the windsurfing tip of the day.
This fin being too low in the board has been a problem for me until I started dropping a rubber band in one end of the taper.
Sometimes 2 rubber bands is needed. It works a treat and a box of them costs almost nothing.
Great idea !
I got to use the modified Supersport board this arv at Semaphore South SA. About 15kt seabreeze, and then picked up to about 18kt. I used a Tribal 29 Speedweed and 5.3 wave sail. Not the best sail combo, as wave sails tend to be a bit impulsey on freeride gear and makes board feel unsettled. But I wasn't even planning to get planing TBO, but it picked up, and ended up nicely powered. This arv's test was good and board worked how it should. A better test would be to use my race sails, but I'll do that in a few months time at North Haven when the northerlies come back on smoother water.
Thank you all again. A special thanks to Col (Imax1) for walking me through the process of fin box conversion, and sharing his knowledge.
