You do notice a damaged fin a fare bit, they also tend to spinout, i try to keep all my fins in top condition, any chips get sanded or filled then sanded, sometimes the graphics even make them spinout, well if there printed on top of the glass that is..

On the speed forum a month or so ago, there was a pic of the guys fin who did 50kt, apparently he hit a rock or something and the fin was a mess. Nobody could believe he'd gone that fast on it.

I've got this device, it's lots and lots of thin steel rods held in a loose clamp, when you press it down on a surface the ends of the rods take on the shape of the surface. This way I can compare sides of the fin against each other and against the required foil shape.

If I'm starting from scratch with a slab of fiberglass I use a sweeping action with a 7" right angle grinder from base to tip. once I get close to the required shape, I use a soft sanding block across the fin.
If it's just repairing a nick that I've refilled, it's the hand block again, but I just bring it down to the old surface which ever direction seems best.

If I'm resanding the whole fin, depends how deep the nicks are, real deep I may use the grinder with even sweeps from base to tip, then hand sand back across the fin, if they aren't very deep it's just a hand sand.

If it's a molded fin be careful of taking the outside skin off, most of them I've seen rely on the outside layers for their strength.

decrepit said...

I've got this device, it's lots and lots of thin steel rods held in a loose clamp, when you press it down on a surface the ends of the rods take on the shape of the surface. This way I can compare sides of the fin against each other and against the required foil shape.

If I'm starting from scratch with a slab of fiberglass I use a sweeping action with a 7" right angle grinder from base to tip. once I get close to the required shape, I use a soft sanding block across the fin.
If it's just repairing a nick that I've refilled, it's the hand block again, but I just bring it down to the old surface which ever direction seems best.

If I'm resanding the whole fin, depends how deep the nicks are, real deep I may use the grinder with even sweeps from base to tip, then hand sand back across the fin, if they aren't very deep it's just a hand sand.

If it's a molded fin be careful of taking the outside skin off, most of them I've seen rely on the outside layers for their strength.

so it's just line of sight for figuring out how much to sand off on both sides then..i've tried doing it once before manual wet sanding with i think 300# attached to a table vice grip hard work with sweats all over and sticky itchy stuff it turned out nice but when on the water i noticed it didn't have the neat water slice sort of cavitating on one side

Sailhack said...
[>>>>>
has worn the outer coating off the bottom leading edge of the fin, back to the glass fibre, or mesh. Will this affect the fin greatly?

Probably not, to any great extent.
But if it's thickened the front edge up significantly, or has a rough surface that will increase drag somewhat.