Underwater hull sanding is performed in several ways.
It depends mostly on construction material, boat type and the type of antifouling already on the boat if the boat is not new.
In case we are dealing with a plastic boat with hard antifouling, existing layer of antifouling is removed after underwater washing; it is then slightly dimmed with random orbital sander using sandpaper (grit designation 80-100), and the underwater hull is thoroughly degreased.
In case we are dealing with a plastic boat with self polishing (soft) antifouling, the existing layer of antifouling is dimmed with random orbital sander after underwater washing. Sanding is at times performed manually using sandpaper (grit designation 150-200), and the underwater hull is thoroughly degreased.
When dealing with aluminum boats, the same technique is applied, using sanding paper for aluminum.
We use only attested machines and vacuum cleaners when sanding.