Sandpaper grits/quick and dirty surface repairs

It's been a bad week for my 12 year-old Hurricane OC1 -- scuffed the side of the 'ama on a concrete bridge abutment during a race, and then hit a rock with the tip of the rudder. Some time- and cost-effective repairs are in order, and what I'm hoping for is advice and feedback for the following plans:

1. For the 'ama: Scrape is at and above the waterline, and does not penetrate the paint. My plan is to sand down the gelcoat (?) until the surface is smooth, then cover the scrape with ___________________. I could use some help filling in the blank with something inexpensive and readily available (the two things that have come to mind so far are clear nail polish and a big decal from a local microbrewery). Also -- what grit sandpaper to use?
2. For the rudder: Leading edge of tip is blunted and a piece of the gelcoat (?) has broken off, leaving the carbon fiber exposed. What grit of sandpaper (or what kind of file) should I use to "re-sharpen" the leading edge, and what substance should I paint on to re-cover the carbon fiber?

This is an old boat, and I am interested in repairs that are cheap, fast, and floatationally and hydrodynamically effective. Let me head off the "Get on the waiting list for a Pueo/Storm" replies by pointing out that that meets neither of the first two criteria.

Thanks,
Nate

Submitted by Nathan Day on Sun, 04/29/2012 - 3:22pm