How should I prep for application of bottom paint?

On Bare Fiberglass/Gel Coat: Remove all surface contaminants, including water, dust, wax, grease, surface blush, etc.

Wipe the surface clean with a lint-free cotton rag dampened with a dewaxing/surface prep solvent (such as TotalBoat Dewaxer & Surface Prep), follow with a clean, dry rag to remove any surface wax. Sand lightly with 80-grit sandpaper. Wipe the surface clean again with the dewaxing/surface prep solvent.

Use masking tape to tape off the waterline. If the boat will be kept in the water, it's best to apply an epoxy barrier coat primer. Follow the manufacturer's application instructions for the primer and bottom paint you're using.

On Bare Steel: Sandblast the surface until shiny and clean. Wipe the surface clean with a lint-free cotton rag dampened with a dewaxing/surface prep solvent, follow with a clean, dry rag. Tape off the waterline. Follow the manufacturer's instructions for applying an epoxy barrier coat primer, followed by the application of bottom paint.

On Bare Aluminum: Remove any loose dirt and clean the surface. Sand with 80-grit sandpaper or abrade with a Scotch-Brite™ pad or sandblast to a bright shiny finish. Remove all sanding residue with a brush or vacuum. Etch the surface with an aluminum etch wash, following the manufacturer's directions. Dry the surface completely. Tape off the waterline. Within 1 hour of aluminum prep, apply an epoxy barrier coat primer, as directed by the manufacturer. When the final coat of barrier coat primer is 'thumbprint tacky' (you can press the surface with your thumb and leave a thumbprint, but there's no paint stuck to your thumb), apply bottom paint.

On Bare Wood: Sand the surface with 80-grit sandpaper. Wipe the surface clean with a lint-free cotton rag dampened with a dewaxing/surface prep solvent. Thin bottom paint with the manufacturer's recommended thinner, and apply the first coat thinned 10 to 20%. Apply the second and third coat unthinned.

On Previously Painted Surfaces: Remove any previous paints in poor condition by sanding, scraping, or using paint stripper. Abrade the surface with a maroon 3M Scotch-Brite pad (medium grade) or 80-grit sandpaper. Wipe the surface clean with a lint-free cotton rag dampened with a dewaxing/surface prep solvent, follow with a clean, dry rag. Tape off the waterline, and apply bottom paint.