Repair a Transom

Fibreglass Boat Transom Repair


Determine the extent of the damage.

Minor Repair - If it is just deteriorated around the holes, you may get away with using the following technique otherwise proceed to step 2;

  1. Enlarge the holes and then dig out the rotten / deteriorated material around the holes.
  2. Tape the outside holes with duct tape and use a syringe with a draw up needle through the inside holes and saturate the timber with Bote Cote Marine Epoxy Resin mix with TPRDA.
    1. NOTE: A good way to detect the extent of rot is to use a coin and tap the fibreglass, if it sounds solid then the timber is Ok. If the sound is dull the core is soft or not solid. See figure One below showing the holes through the Transom.
  3. Then apply Duct Tape to seal the holes on the inside leaving the top open.
  4. Use a syringe with a draw up needle through the gap in the tape on the inside holes and fill the holes with Bote Cote Epoxy Resin.
  5. Leave cure overnight and preferably a couple of days and then redrill the holes through the centre.
    1. NOTE: This will ensure the transom is waterproof where the holes are and the epoxy also acts as a spacer preventing compression damage.
      Figure 1

      Figure 1 – Before the repair was commenced with the inner and outer skin being spongy. Rot occurred due to moisture accessing the ply core through the holes.
      Also note the compression around the holes.


If the fibreglass is not damaged, replacing rotten wood inside the transom can be another quick way to make repairs that will help your boat last much longer. Draw a line where you will make the cut if the damage requires complete repair of the transom.
Note: If the outer skin is OK remove the inner skin as shown in Figures 2 & 3.

Figure 2

Figure 2 – Notice that the wood inside the transom was about the consistency of compost ready for the garden.


Cut out the inner transom and remove the wood. Use the removed piece as a pattern to cut a new piece (if recoverable).


Seal the new plywood core with three coats of

Figure 3

Figure 3 – Transom cleaned up ready to fit new plywood core and then the inner skin.

Bote Cote Marine Epoxy Resin, especially the edges. Course sand all surfaces including the edges to provide a good keyed surface for the Bote Cote Marine Epoxy Resin to bond to.

Note: (i) It is recommended to fit up the core and make sure it fits into the cavity easily.(ii) While there drill holes through the core from the outside of the transom skin. These can then be used to hold it in place once glued.

Figure 4

Figure 4 – Transom showing thickness of new plywood core required.
Tip: The easiest way to achieve the thickness is to use a sheet of 6 or 9mm Marine plywood laminated to gether to build up to thickness. As 25mm Marine Plywood is fairly expensive per sheet and you would have heaps left over.


Mix Fillet & Gluing Filler into Bote Cote Marine Epoxy Resin until it is the consistency of tomato sauce or thicker, then apply a thick layer onto the inner surface of the transom outer skin and then fit up the new core.

Note: A good alternative is to use Epox-E-Glue instead of mixing Filler in to the Bote-Cote as it saves time and will not sag. Also it is ultimate strength.


Apply duct tape around all the bolt holes and make up pad pieces using left over plywood and drill holes through that match the holes in the transom. Place Vaseline on bolts and put them through the holes and new core and pull up firmly using another pad piece inside. This will hold the outer skin and core together while the epoxy dries. Leave on overnight.

Note: (i) wrap the pad pieces in Glad Wrap or similar as it will stop the epoxy sticking to them. (ii) Do not over tighten the bolts and nuts as epoxy needs some gap for strength and over tightening the bolts will squeeze out the glue and deform the outer skin where the pad pieces are.


Sand the cured inner skin of gloss and repeat Steps 5 & 6. Then fibreglass the joins around where inner core was cut out. Then repeat step 1 for minor repairs.


Last but not least paint with Aquacote, then replace the hardware and head for the water. Note: Last piece of learned advice – Do not skimp on the quality of plywood. Saving a few $$$’s now could mean redoing the whole thing again down the track. The most valuable thing you will be providing, is your time - Do not waste it.