Hull Repair – Severe

Project 1: Repair Aft Keel Damage (Section broken off from grounding on reef)
Project 2: Repair Forward Keel Damage (A few layers of fiberglass impacted from smacking an unmarked sunken barge)

  1. Supplies:
    1. Angle grinder
    2. 40-50 grit flexible sanding discs for angle grinder
    3. Carpet drying fan
    4. Extension cord
    5. Drill and bits
    6. Eye protection
    7. Multipurpose 4:1 Epoxy resin and hardener (or West System 105/205)
    8. Resin measuring cups, containers and mixing sticks
    9. Resin brush
    10. Acetone
    11. Flathead screwdriver to open acetone lid
    12. Lint free rags
    13. Shop towels
    14. Scissors
    15. 1 ½ oz fiberglass mat
    16. 6 oz fiberglass cloth
    17. West System 407 structural filler
    18. Fiberglass roller
    19. Orbital sander
    20. 80 grit sandpaper for orbital sander
    21. Refillable caulking gun or tube for injecting resin
    22. Ground cloth

Project 1: Repair Aft Keel Damage (Section broken off from grounding on reef)

  1. Dry repair area
    1. Cut the fiberglass using an angle grinder to let the area drain and dry. A dremel is way too small and will not work on damage greater than a quarter in size. Also think about drilling holes to speed the drying process.
    2. Here’s the area spewing water after grinding away the damaged fiberglass.
    3. Plug in a fan or carpet dryer with an electrical extension cord and dry for hours or days.
    4. Check for moisture by drilling access holes with a drill and bits or using an electric moisture detector. Do not fiberglass over a wet interior or the fiberglass can weaken and delaminate over time.
    5. I ran the carpet dryer for 2 days and 2 nights. I later saw a small drip of moisture coming out of the repair as the epoxy dried. A third day of drying would have been better.
  2. Rebuild the aft edge of keel
    1. Prepare the area for laying new fiberglass
      1. Grind the area smooth with a 12:1 bevel using an angle grinder and 40-50 grit flexible sanding discs. For example, if your laminate is 1/8″ thick you will grind 1.5″ in towards solid glass with a nice even bevel. Use eye protection.
      2. The smoother your preparation is, the quicker and easier the next step will be.
    2. Apply un-thickened epoxy resin and hardener first to soak into the exposed foam. Mix the proper amount using measuring containers and mixing sticks, then use a cheap paintbrush to slop on the epoxy. Shop towels are handy to keep things clean.
    3. Cut out the fiberglass fabric with a pair of scissors so they are ready before mixing up the epoxy resin. The first two layers should be 1 ½ oz fiberglass mat, then alternate 6 oz cloth and mat. The mat acts as a glue to strengthen the connection between the stronger cloth layers.
      1. The first layer is the largest, the next about an inch smaller to match the 20:1 bevel you ground out previously. Putting smaller layers on top may be counter-intuitive, but it maximizes the area of the secondary bond.
    4. Mix in some West Marine structural filler with a fresh mix of epoxy and apply a layer to the damaged area in preparation for the first layer of fiberglass. This helps smooth out the surface to prevent voids and air pockets. It should be the consistency of thick molasses, but not quite as thick as peanut butter. See the product instructions.
    5. When the filler kicks (begins to gel hard), add the first two layers of mat, apply epoxy resin and smooth out the bubbles with a fiberglass roller.
    6. When the first layers kick, apply four additional layers, rolling resin after each layer. Don’t add more than four layers before kicking or the heat generated by the drying resin could cook and weaken it.
      1. I paused with the layering here to fill the large void with filler (see the next steps below). It was easier to see the void filling with epoxy with the sun shining through it. I later continued layering the structural fiberglass.
    7. The last layer should be mat. Mat is easier to grind down after drying.
      1. In total, I added 7 layers of fiberglass
    8. Once fully cured, sand with 80 grit on an orbital sander or grind the area to the correct shape, then use West Marine filler to perfect the final shape.
    9. Fill interior voids with epoxy/filler
      1. If there are interior voids in the keel, inside the repair, they will need to be filled. Use a large syringe to squeeze epoxy resin into the access hole(s). Add a 1/2 fluid oz at a time to keep it from boiling as it cures. Consider using the carpet fan to keep it cooler. (I added 1 fluid oz at first and it kicked too fast with some slight bubbling and smoking.)
    10. Finish filling the access hole with filler, dry, sand smooth, seal with epoxy resin, sand and paint to complete the repair.

Project 2: Repair Forward Keel Damage (A few layers of fiberglass impacted from smacking an unmarked sunken barge)

This project was much simpler than building up a corner of the keel. Simply grind out all the rotten fiberglass, sand, fill, lay-up fiberglass, sand, seal and paint. Easy! :)

Here’s what the soggy fiberglass looked like after soaking for 6 months. Siren hit an unmarked sunken barge going dead downwind at 6 knots.