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Fiberglass boat keel repair - Featured image

Fiberglass Boat Keel Repair

Has your sailboat or powerboat sustained damage to its vulnerable keel? Impact with underwater objects can crack, chip or puncture a fiberglass boat’s keel, compromising structural integrity.

When keel damage occurs, proper repairs are essential for restoring seaworthiness.

This article provides a DIY overview of assessing damage and performing a fiberglass boat keel repair.

Fiberglass Boat Keel Repair Guide

1. Inspecting Keel Damage

After a grounding or collision, thoroughly inspect the keel for cracks, fractures, holes and delamination. Look for stress cracks radiating from the point of impact. Check inside the boat along the keel joint for signs of damage. Determine how extensive the repairs need to be.

Minor chip repairs may only require some basic grinding, filling and refinishing.

Major cracks, holes and delaminated bottom skin necessitate more extensive fiberglass work.

If damage compromises over 30% of the keel depth, professional repairs may be needed to meet safety standards.

2. Grinding Out Damaged Areas

Start by sanding and grinding down all cracked, chipped and punctured areas with 36-80 grit disks to open up the damage.

Remove loose fibers and degrade the gel coat surface to improve adhesion. Create a rough surface profile for the repair compounds to mechanically bond with.

For cracks, the saw cut a V-groove along the length with a circular saw at least 1/8″ deep to increase the surface area. Grind damaged fibers at the root.

Vacuum and solvent wipe repair areas to remove debris and grease before applying materials.

3. Filling Holes, Cracks and Chips

Fill scratches, gouges, cracks and drill holes with thickened epoxy adhesive filler thickened with colloidal silica or micro balloons. Apply filler in layers until flush with the surface, allowing cure time between applications.

For cracks, wet out the inside surfaces with neat epoxy before applying thickened epoxy. Overfill the repair and allow the adhesive to cure before final sanding.

Finish filling holes and cracks by applying structured repair materials.

4. Applying Fiberglass Repair Laminates

Fiberglass boat keel repair - Woven and fiberglass cloths

Cut several plies of woven fiberglass cloth to overlap damaged areas by at least 2″ on all sides. Pre-fill any cloth texture with epoxy filler.

Wet out each layer of cloth with epoxy resin before applying it to the repair. Use a plastic spreader to smooth the cloth, removing air pockets and excess resin. Apply 4-6 layers of cloth based on existing laminate thickness.

For cracked keels with bottom skin delamination, the detached skin may need re-bonding and supplementary layers of glass cloth overlap for added structural strength.

Allow resin fill coats to fully cure between layers based on product guidelines.

5. Fairing & Refinishing Repairs

Once the repair plies fully cured, use 80-120 grit sandpaper to fair in the repair and blend with surrounding fiberglass. Fill any remaining pinholes or surface irregularities with polyester or epoxy filler/fairing compound, then sand flush.

Solvent clean and apply three coats of two-part polyurethane topside paint to match your boat’s color.

Lightly sand between paint coats. Touch up registration numbers, draft marks and antifouling bottom paint as needed.

Final Thoughts

Performing quality fiberglass repairs takes some work, but restored integrity and seamless refinishing is achievable with the right techniques.

Follow safety precautions when grinding glass materials and mixing/applying resins. Use protective equipment and ensure adequate ventilation.

With time, patience and the proper methods and materials, you can repair damage to your boat’s vulnerable keel without breaking the bank.

Take things slow, allow adequate cure times and the result will pay off with a keel that’s shipshape. Your fiberglass sailboat or powerboat will be back cutting smoothly through the seas in no time!

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