Scratches and scuffs surely look messy on plastic (polyethylene) kayaks, although they rarely amount to more than cosmetic damage. But even small scratches, like those made just by running the boat up on a sandy beach, cause lots of friction which slows down your kayak. You can use a Hyde Razor Scraper ($1.21 at your local hardware store) to shave off even the smallest plastic curls. This is best done while the boat is cool.
If your linear polyethylene kayak has a deeper gash (1-3mm deep), these can be filled by melting polyethylene plastic in a melting pot and then applying it over the gash with an applicator.
We recommend attempting this method only if you have enough experience with since these boats melt very easily. Make sure to use polyethylene plastic, preferably from a kayak to fill in the crack. Be sure that the plastic you use is clean and free of dirt and other small particles. Of course, your kayak should also be clean and dry before you apply plastic to it.
Our Irvine Walk in Store offers professional quality plastic repairs at affordable rates.
To complete your refinishing, a thin coat of 303 Protectant, or other non silicon and non-petroleum products can certainly make any boat look a whole lot nicer and will also add a measure of UV light protection, in the case of 303.