i took a massive chunk out of a fin on rocks a while ago.

here's what I did:

* Get some fibreglass cloth and resin.
* Sand around the damaged bit of the fin so the resin will stick better, and make sure the fin is totally dry.
* Put the fin in a vice horizontally.
* Place masking tape along underneath side the damaged edge so it can catch the resin.
* When you're putting the tape on, try to make it so there's a gap that allows the resin to flow underneath the fin as well. Hard to explain without showing you, but when you stick the tape down, the edge of the tape closest to the fin's edge should not be touching the fin. Lift the tape off the fin so only the back edge of the tape and the ends (which should reach beyond the damaged section) are touching enough to support the resin. That way you don't have to repeat the process for the other side and it will set as one section, rather than ending up with 2 sections of resin that set at different times (which would create a join that may not last)
* Cut up bits of fibreglass cloth in tiny pieces to mix in with the resin (I was told that helped it either strengthen it, or set, or both).
* Pour the resin mix onto the damaged part of the fin. It will sit in a pool on top of the tape, and also flow to the underside of the fin (where the tape is lifted off).
* Make sure that the resin covers both sides of the fin thoroughly.
* When its dry, you'll have an ugly chunk of sh1t hanging off your fin.
* Sand it off (power sander would be better to get most of it off, otherwise it will take ages).
* Sand it right back to the shape the fin should be.
* I then buffed it so it was perfectly smooth.

Shape was perfect. Couldn't tell it was repaired if you shut your eyes.

When I think about it now, it was actually a pretty crap fin anyway. Should have just bought a new one. At least I learned how do fix it though
I've got chunks out of the back edge of one of my current fins. Don't know how I'll fix that. oh well.

p.s The tape bit may not be the best way to do it, but it worked. Maybe tape something more solid. like bits of cardboard or something around the area so you don't have to worry if the tape is lifting off too much (or not enough). But same method. Form a pool underneath the fin. Make sure it won't move until the resin is dry.

Hope it made sense

Nice artwork!

But no, I mean with the side (surface area) of the fin facing up. So that the tip is pointing at the wall.

like this:

------------- (that doesn't help does it?)

But, perhaps it is possible to do it like you suggest. as long as the damage isn't too far along the edge, otherwise your resin would have to defy gravity.

what you'll find is that the resin will want to run to the under side of the fin anyway, because of gravity. so when it dry there will be more on one side than the other. But just make sure that you put plenty on top so it doens't matter. Too much doesn't matter. Too little, and you'll have to start again or add another layer once its dry.
Its not hard. just fiddly.

quote:

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Originally posted by Leech

Smacked the reef with my favourite fin last night and got a nice big chunk taken out of it.

What's the best stuff for fixing it?

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If it's a real big chunk, I get into the fin with an angle grinder with sanding pad attached,
do one side at a time, the worst side first, sand back to about 10mm from the damage and to 1/2 way through the fin.
Pack up the damaged area with something plastic that resin doesn't stick to.
Lay this up with enough layers of fiberglass to get back to original thickness.

When that's hard sand other side down to new glass and fiberglass that.

Sand and smooth, fin's as good as new.

You can also use this method to rebuild the whole bottom edge when it gets ground down too far, from several minor scrapes or sailing in ultra shallow water.

If the damage isn't huge qwerty's method is probably quicker, (do both sides at once) but it's not as strong because you can't get anywere near as much fiber tying the whole thing together.