How to Clean the Marine Growth on an Outboard Engine

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Outboard motors are effective drive systems. They provide directional thrust for steerage under power, and the lower leg has a foil shape that gives steerage when you have headway and the motor is in neutral. This foil shape and the propeller rely upon laminar flow to operate properly. Marine growth, such as barnacles and mussels, disrupts this laminar flow and ruins the effectiveness of the foil shapes leading to poor steerage and loss of speed due to drag. Marine growth is easily removed and must be done at least once a season, usually at the beginning of the season.

Things You'll Need

  • Power washer
  • Scraper
  • Dust mask
  • Sandpaper (80 grit)
  • Orbital sander
  • Paint (motor paint or bottom paint)
  • Paintbrush
  • Pressure wash the affected areas. Blow off all mussels, slime, and grass with a pressure washer.

  • Scrape off the barnacles. Remove the tops of the barnacles but do not try to scrape off the bases. Be careful you do not gouge the lower leg, which is made of aluminum and tends to be a little soft. Pressure wash the area again and allow it to dry.

  • Put on the dust mask. Sand off the barnacle bases. Move the sander in a pattern across the area until all the bases and paint is sanded away. Ensure that the surfaces are smooth and free of any bumps or irregularities.

  • Paint the lower leg. Spray on original equipment manufacturer's paint with an aerosol can or paintbrush, or with a good quality bottom paint. Apply the paint in thin coats to avoid runs and sags that will require sanding, adding considerable work to the project. Allow the paint to dry fully before re-immersing the motor.

Tips & Warnings

  • Do not breathe the fumes of the paint or the dust from sanding. Bottom paints contain lead. Inhaling paint dust can be hazardous to your health.
  • Use an orbital sander. Do not use a rotary sander. Rotary sanders are very aggressive and can grind scallops into the surface of the lower leg, permanently reducing its efficiency.

References

  • Capt. TJ Hinton; commercial fishing vessel captain; Gulf Coast, MS
  • Photo Credit Jupiterimages/Photos.com/Getty Images
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