Hull, gelcoat & antifouling

How to clean a boat hull: topsides and bottom

Updated: 4 min readCaranva Boats

Quick answer

Clean the topsides with fresh water, marine soap and a soft sponge, using a dedicated cleaner for bow yellowing and fender marks. The bottom is cleaned ashore with a pressure washer or in the water by a diver, taking care not to strip the antifouling. Finish with wax to protect the gelcoat.

Topsides (above the waterline)

  1. Rinse with fresh water to remove salt.
  2. Wash with biodegradable marine soap and a soft sponge or brush.
  3. Remove bow yellowing and waterline scum with a dedicated (usually gel) cleaner.
  4. Remove fender marks with a gentle cleaner or melamine sponge.
  5. Rinse and dry with a chamois to avoid water spots.
  6. Protect with wax. See how to polish and wax a boat.

Bottom (below the waterline)

  • Ashore: pressure wash immediately after lifting, before the growth dries.
  • In the water: a diver cleans hull, propeller, shafts and intakes with soft brushes or pads. Find professional divers.

Be careful with ablative antifouling: too much scrubbing wears it out early. See how often to antifoul a boat.

Recommended frequency

  • Freshwater rinse: after every trip.
  • Full wash: weekly in season.
  • Diver bottom cleaning: every 1–3 months in summer.

To book it, see our boat cleaning service.

Frequently asked questions

What removes yellow stains from a hull?

Gel hull cleaners based on oxalic acid or similar, left for a few minutes and rinsed thoroughly. Protect teak and metals when using them.

Can I clean the bottom myself in the water?

Many marinas restrict it for environmental or safety reasons. Check with the marina and, if allowed, use soft tools so you don’t damage the antifouling.

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