How to Build a Taller Transom for a Johnboat

Johnboats are low-to-the-water fishing boats. Some johnboats may have high-back fishing chairs on the bow, while others may have flat hulls and thwarts. Thwarts are the benches that run between the sides of the boat hull. The transom is where the main motor is mounted, allowing the captain to control the engine from the rear of the boat. Modifying the transom so it is taller enables longer engine shafts to be used with the boat, making for better control and steering.

Things You'll Need

  • Marine pressure-treated plywood sheets
  • Tape measure
  • Carpenter's pencil
  • Power saw
  • Power sander
  • 1/2-inch bolts, nuts and washers
  • Power drill
  • Marine caulk and caulk gun
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Instructions

    • 1

      Measure the current transom, getting the height, width and length. Measure out a taller transom on a sheet of marine pressure-treated plywood by extending the top end to your desired height. For example, if you wish the transom to be 4 inches taller, measure and mark the top at 4 inches taller than the existing transom. Use marine plywood on the project because it is made to withstand the rigors of repeated water exposure.

    • 2

      Mark the transom measurements; include the taller height you need. Cut out the pattern using the power saw. Place the cut-out transom piece onto another sheet of the plywood, trace it and cut out the second sheet.

    • 3

      Place one piece of the new transom onto the inside of the boat hull. It is going to fit extremely tight, so use the power sander on the edges to smooth it out and reduce the edges until the transom piece fits snugly, but comfortably into the hull.

    • 4

      Drill two screw holes through the new transom piece and the boat hull, one in each upper corner on the transom piece. Push a bolt through each hole; include a washer between the screw head on each screw.

    • 5

      Caulk the drilled holes on the outside of the hull, making sure it fills in around the screws. Position the second transom piece of plywood against the outside hull of the johnboat, and mark the screw locations. Drill out the screw location holes, and align the holes to the screws, pushing the transom piece tight against the outside of the hull.

    • 6

      Add another washer to the outer portion of the bolts as they stick out from the drilled holes on the outside transom piece. Add nuts to each bolt and tighten as hard as possible.

    • 7

      Seal the lip, or gap, between the inside and outside transom pieces using marine caulk. Let the caulk cure, or dry, overnight.

    • 8

      Mount the engine to the new transom using the engine's proprietary system of brackets and mounts. Different engines have different forms of mounting to a transom.