ΕΔΔΥ . <overlordmustafa@...>
I've done many repairs on fibergass, I used to build RC models.
One great method to get a smooth final coat of glass is to get the absolute lightest fiberglass you can get your hands on.
After laying up whichever weight of glass (which most people use is rather a heavy weight, compared to what i'm used to using) you can place a layer of 0.5oz/sq ft fiberglass as a top coat. This adds virtually no weight, you don't have to add any epoxy. This 'trick' works significantly. It's like getting strength at no extra weight.
If you're worried about sanding through the fiberglass you could add a layer of this light cloth. Apply it differently than thicker cloth. Brush on the thinnest layer of epoxy onto the fin then place the glass over the wet surface. Slow cure is better over fast cure for this (I prefer slow cure over anything else).
So, if you're worried about digging though fibergass, this is an easy fix. When you're done it's amazingly smooth. You'll still need to sand it to get it perfect, but it's close to perfect.
You might want to even bump up the weights(of glass) a bit. The lightest glass is so thin you can't move it around very easy when placing it (so be delicate when setting the glass down). An advantage to using the extremely thin stuff is it goes around corners and bends like nobody's business.