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How to Make an Inboard Boat Engine Cover

by William Machin
Shipwrights fabricate wood and fiberglass engine covers.

Shipwrights fabricate wood and fiberglass engine covers.

Inboard engines are used to power commercial vessels and recreational boats. Typically, inboard engines for commercial vessels are installed below the deck. Inboard engines for recreational boats install below deck or at mid-deck, with the upper part of the engine above the deck. Engine covers for commercial vessels are engineered using thick steel plate or heavy composite materials. You can make a flush or raised inboard engine cover for a recreational boat or pleasure boat using fiberglass and marine hardware.

Flush Cover

Measure the width and length of the opening above the engine for a flush engine cover. Deduct 5/8 inch each way for fiberglass. Cut a piece of 1/2-inch plywood to the corrected measurements as the fiberglass mold. Use a circular saw or table saw to cut the plywood.

Refer to the instruction for the fiberglass kit and apply three layers of reinforced fiberglass to the surface and sides of the plywood mold. Allow the fiberglass to harden completely and remove the plywood mold. Sand the rough edges and surface of the fiberglass cover using a belt sander with medium grit sandpaper.

Position a pair of stainless steel butt hinges along one edge of the cover with the hinge pins aligned at the outside edge of the cover. Each hinge should be 2 inches from the respective end of the cover. Drill pilot holes for stainless steel bolts at each of the pre-drilled holes in the hinge butts. The size of the pre-drilled holes in the butts determines the size of the pilot holes and stainless steel bolts.

Insert stainless steel bolts into the pre-drilled holes in the hinge butts and through the pilot holes in the fiberglass cover. Put flat washers with nuts on each bolt at the underside of the cover. Tighten the nuts with a socket and ratchet. Attach a flush ring pull to cover if desired.

Raised Cover

Measure the opening above the engine for a raised cover. Add 1 inch each way to allow the bottom edges of the cover to rest on the deck. Measure the distance from the surface of the deck to the top of the air cleaner on the engine and add a minimum of 6 inches for clearance. Note the width, length and height measurements of the cover.

Make a three-sided raised cover for the engine using 3/4-inch marine grade plywood. Refer to your measurements and cut the front and sides of the cover. Assemble the pieces with wood glue and 1 1/2-inch wood screws at the corners. Use a cordless drill with a screw tip attachment to drive the screws.

Stand the three-sided cover and re-check your dimensions to make sure the cover is uniform. Cut a plywood top that is flush with the outside of the front, sides and back edges of the three-sided cover. Attach the top with wood glue and wood screws.

Refer to the instructions for the fiberglass kit and apply one layer of fiberglass to the sides and top of the raised cover. Allow the fiberglass to harden completely. Sand any imperfections in the fiberglass using a belt sander with medium grit sandpaper.

Drill 1-inch ventilation holes along the upper edges of the cover. The holes should be 6 inches apart and 3 inches below the surface of the cover on all sides. Attach a flush ring pull to the front of the cover if desired. Set the cover in place over the engine.

Items you will need

  • 1/2-inch plywood
  • Circular saw
  • Fiberglass kit (Reinforced fiberglass)
  • Belt sander with medium grit sand paper
  • Stainless steel butt hinges
  • Cordless drill with screw tip attachment
  • Drill bits
  • Stainless steel bolts with flat washers and nuts
  • Socket and ratchet
  • Flush ring pull (Optional)
  • 3/4-inch marine grade plywood
  • 1-inch drill bit

Tips

  • Finish a flush cover with non-slip deck surfacing.
  • Finish a raised cover with auto primer and paint.
  • Consult a boat shop or shipwright for additional suggestions on fabricating engine covers.

Warning

  • Wear a dust mask and safety glasses when sanding fiberglass.

About the Author

William Machin began work in construction at the age of 15, while still in high school. In 35 years, he's gained expertise in all phases of residential construction, retrofit and remodeling. His hobbies include horses, motorcycles, road racing and sport fishing. He studied architecture at Taft Junior College.

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