Don't use the 5 micron size, the particle size is too small and causes a lumpy mixture. Get the cheaper stuff as Sam suggests. If you use the HBN, to achieve the whitest final surface you will probably have to layout multiple coats, maybe 3-5 depending on what color the hull is now. It's a little tougher to get a uniformly white (HBN) final coat than it is to get a uniformly black (graphite) coating.

Robert N Pruden