Auhhh, now we know why that 5.8 move so well in light air...lol..You may wish to try Simple-Green or GUNK in a spray can..both are good with carbonized soils. GUNK (solventized emulsion) being a good deal stronger. After the hulls are cleaned well, take a look at the new Poly-barrier coatings. These protect the porus jel-coat (on older or sanded hulls)and help retard future staining...