How to Seal an Outboard to Transom Bolts

by C.L. Rease
Leaking outboard motor mounting bolts can ruin a day on the water.

Leaking outboard motor mounting bolts can ruin a day on the water.

Keeping water from entering the boat through the outboard motor mounting bolts requires a sealant capable of long-term exposure to both fresh and saltwater. Using the incorrect type of sealant will stop water leaks for a short time but the leaks will soon return and continue to cause damage to the boat's transom.

Select a socket that matches the size of the outboard motor mounting bolts. Secure the socket to a ratchet handle.

Turn the lower left mounting bolt counterclockwise until it pulls from the transom.

Wipe the threads and smooth shank section of the bolt with a clean rag. Ensure the bolt is dry. Inspect the transom hole to ensure it is also dry. Allow the boat to sit in a dry location for 24 hours if the transom hole contains water.

Puncture the top of a marine sealant tube with the point on the cap. Apply a bead of marine sealant around the smooth shank section of the mounting bolt. Slide the bolt into the transom hole. Tighten the bolt with the socket and ratchet handle.

Repeat the procedure with the mounting bolt located on the lower right mounting bolt.

Items you will need

  • Socket set
  • Ratchet handle
  • Clean rag
  • Marine sealant tube


  • Allow marine sealant to cure for 24 to 48 hours before placing the boat in the water.


  • Secure the boat to the hitch of a vehicle with the parking brake set to keep the boat stable while sealing mounting bolts.

Photo Credits

  • Jupiterimages/ Images