Replacing a Damaged Rib:               Return to 'Projects/Repairs'

   Extensive dry rot was recently discovered in the forward rib of the Hudson double/pair
owned by the Aqueduct Rowing Club. The rib supports the end of the forward slide and
holds the mounting bolts for the forward rigger when the boat is rowed as a pair. In the original
Hudson construction, the rib was composed of a core of 0.75" birch plywood, covered with a
layer of fiberglass, and painted on the lateral  faces. It is believed that the rot started in the
rigger mounting holes and progressed downward into the sides and base of the rib. The fiberglass
coating masked the core failure until the rigging bolts began to compress and buckle the rib.
The failed rib is shown in Figure 1 after removal of the seat tracks. Arrows point to the rotted
areas. The top left side of the rib, which appears intact, was found to have disintegrated internally.

               
                                                         Figure 1

    In order to fabricate a replacement, a profile of the hull was developed at the location of
the rib using a pin gauge. The body of the gauge was held perpendicular to the splash-box coaming
using a batten and square as shown in Figure 2.

               
                                                           Figure 2

    The gauge profile was traced onto a piece of cardboard to create a pattern for the new rib. The
pattern itself was made in two halves in order to accurately reproduce small differences in the port
and starboard sides of the boat. This method had the added advantage of allowing the exact width
of the original rib to be matched by overlapping the two pieces and taping them together while
the port and starboard edges were held against the inner surface of the hull. The finished pattern
is shown in Figure 3.

               
                                                      Figure 3

 
    The rotted rib was next removed as carefully as possible by using a utility knife to cut along
the fillet bonding it to the hull and carefully chiseling out the remaing wood and fiberglass. The hull,
with the rib removed, is shown in Figure 4. Note that rib runs through rather than over the inwales
and bilge stringers. As a result, the cutouts for these pieces were omitted when the pattern was
traced onto the rib blank.

               
                                                      Figure 4

    The rib was cut from the blank using a bandsaw taking care to cut just outside of the traced
line. The final fitting was done by placing the rib in the boat, marking the high spots, and using a small
drum sander mounted in a drill press to remove the excess material. Battens were used to insure that
top of the new rib was accurately aligned with the two other ribs supporting the seat rails as shown
in Figure5. The positions of the holes for the rigging bolts were marked using the holes in the hull
as a guide. They were then thru-drilled using a drill press Additional holes were drilled for the
aluminum cross braces lying below the seat rails.

               
                                                       Figure 5

     The new rib was subsequently removed and the faces and edges were coated with clear epoxy
After curing, the epoxy was scrubbed with Scotchbrite^® and water to remove any amine blush
and roughen the surface. The top, bottom, and faces of the rib were then coated with more epoxy
and 4 oz. glass fabric as shown in Figure 6. It was found best to cut the fabric slightly oversize,
wet out and squeegee the contact surface, and allow the resin to partially cure before trimming the
excess. After final cure, a router and laminate trimming bit were used to cut the edges of the glass/
epoxy coating flush with the rib.The  holes for the rigging bolts and braces were re-drilled to
remove the fiberglass coating and the insides were coated with epoxy to prevent recurrence of rot.

               
                                                      Figure 6

    The rib was bonded to the hull using epoxy slightly thickened with colloidal silica. Additional
silica was then added to further thicken the epoxy and a fillet was applied to the entire hull/rib joint.
The rib was lightly clamped until the resin cured. Finally, additional glass fabric was scarfed into the
top of the gunwale to cover the top edges of the rib. The finished rib and gunwale were painted to
match the original. The completed repair is shown in figure 7.

               
                                                      Figure 7