To remove a car scratch that has not penetrated the clear coat layer, polish the scratch until it disappears, then respray the area with a clear, protective coat. To remove a minor scratch from a boat, remove the wax and grease from the scratched area with acetone. Wet sand the area with 1000 grit sandpaper, then switch to 1500 grit sandpaper. Wash the area with soap and water, then apply boat wax and buffer.
To repair a deeper scratch on a car, remove any oils or wax and apply primer or color to the scratch. Let the paint cure overnight, then use 600 or 1000 grit wet-or-dry sandpaper to even out the paint. Apply paint until the crack is smooth and level, then apply compound to restore a glossy shine.
To repair a deep scratch on a fiberglass boat, remove grease and wax from the area with acetone as with a small scratch. Use a gouge to shape the scratch so that it is uniform, then remove any dust. Fill the scratch with color-matched gel-coat paste, leaving the paste a little thicker than the hull around the repair area. Let the paste cure, then sand with 1000 grit sandpaper and polish until smooth.