How to Repair Large Hole in Fiberglass Boat

"This site contains affiliate links to products. We may receive a commission for purchases made through these links."

Having a large hole in your fiberglass boat can make your beautiful boat go ugly in no time. You will definitely be needing the Fiberglass Glow Bit Repair Kit (Available on Amazon).

Image result for Poli Glow kit boat RV fiberglass/gel coat restoration with UV inhibitors
Fiberglass Glow Bit Repair Kit

Otherwise, it would be impossible to enjoy a ride on your boat as the hole makes it too risky or even deadly.

But the hole doesn’t render your boat totally useless if you know what to do.

There are many advantages of having your boat built with fiberglass (or glass-reinforced plastic).

One of them is that fiberglass hulls are mostly free of corrosion.

Another advantage of having a fiberglass boat is that it has the ability to use a female mold as the foundation for the shape of the boat.

With the necessary materials and information, you could be repairing that deep gash at the side of your beautiful boat.

If done well, your repair will look invisible at the end and the repaired part will be as strong (or even stronger) than other parts of your boat. Without further ado, this post is going to teach you the steps to take to restore your boat back to its beautiful and capable shape.

Materials and equipment needed: raisin, hardener, low-density filler, white pigment, saber saw, sandpaper, sanding disk, brush, gloves, roller, goggle, respirator, cup, and spoon for making mixtures.


  • Survey the hole to determine the extent of the damaged area. Most likely, the hole has rough edges that will make it difficult to get your repair done. You need to smooth out the edges of the hole. This is where a saber saw comes into the application. Outline the repair area and use the saber saw to turn the hole into a circular or oval shape, whatever shape is convenient for you to work with.

Source: Practical Boat Owner


  • Measure the thickness of your laminate as this determines the size of your work area.

  • Multiply the thickness of your laminate by 12 to get the 12:1 for the distance of the work area from the edges of the hole.

  • Grind out the area with a 50 or 80-grit sanding disk.

  • Use a piece of plastic to measure the outer circle or shape of the work area and the inner circle or shape of the work area.

  • This will be used to cut the different sizes of your fiberglass. Between the outer circle and the inner circle, you’ll cut as many as 4, and up to 6 or more depending on the size of your work area. The sizes of the fiberglass sheets you decide to use will range from the largest area as the area of an outer circle to the smallest area as the area of your home.

Source: Practical Boat Owner


  • Before you can repair this hole, you have to cover up the inside of the hull to prevent the wet fiberglass from caving in. A piece of plywood, soft foam, and plastic. All these materials must have a larger size than your work area. To cover the repair area, you position the plastic first on the repair area, then the soft foam and the plywood last. You can either prop the back of the plywood or screw the temporary support into place.

  • Use your glove, goggles, and respirator to prevent the effects of the mixtures on your skin, eyes, or nose.

  • After this, you prepare the mixture of the resin and the hardener. You must add the right amount of hardener to the mixture. The ratio of hardener to be mixed with your resin will be specified on its container. The resin could be polyester, vinyl, or epoxy. Polyester is cheaper than epoxy but can shrink as it heals. It may also bring out pungent smells. Epoxy is sensitive to temperature when healing. I’ll be using epoxy for this post. Adding too much of it could cook your fiberglass and lead to a weak lamination. Adding too little could also lead to an extremely long cure time but it is better to err on the side of being a bit too little than too much.

  • The mixture is applied to the repair surface.

  • The mixture is then applied with a brush to the smallest of your fiberglass. The next fiberglass in size will be added to the mixture added to it. The process is repeated until the last fiberglass is in place. You must remove all the air bubbles from the fiberglass using the squeegee using a plastic squeegee to make it as firm as possible. When you’re through with this, the fiberglass now has a transparent look.

  • Add colloidal silica to the remaining mixture of the raisin and hardener to improve consistency. Add the mixture to your repair area.

  • The combined fiberglass sheets are placed on a plastic that will be used to apply the fiberglass to the repair area. To give your repair the best shape, the fiberglass sheets are positioned in such a way that the largest sheet is directly on the repair surface and other smaller sizes follow.

Source: Practical Boat Owner

  • After applying the fiberglass to the repair area, smoothen the surface with the squeegee to remove air bubbles and excess raisin from the patch. Remove the plastic attached to the fiberglass gently.

  • Clean off excess epoxy out of the work area as that is easier than sanding it off when it has healed on the surface.

Source: Sea Hawk

  • Allow the patch to heal for a few hours or overnight. After the patch has healed, remove your temporary support. You can sand the surface if rough. You also have the option of painting it depending on what you want.

  • Wipe the repair surface and check if there are no rough edges. If there are rough edges, you can use your sandpaper to smoothen them or a sanding disk if your sandpaper is unable to get the job done.

  • Add the mixture of epoxy and hardener to the repair surface. Add low-density filler to the surface to improve consistency. When this is almost dry a few hours later, add a thinner layer of the filler to the surface. Make the surface as smooth as possible and allow the surface to cure for a few hours or overnight. After the mixture has healed, the surface with an 80 grit sandpaper or a sanding disk.

Source: Sea Hawk

 Sand the surface to make it as smooth as possible. Prepare a mixture of epoxy and hardener and add a little amount of white pigment to it. Apply this mixture to your repair surface with a roller to provide a color base for painting.

  • Allow the coat to heal. Add another layer of the mixture to the surface. Your repair work is now done and ready to be painted.

Getting Your Fiberglass Boat Fixed…

Repairing a large hole is easier on a fiberglass boat than on other types of materials used to construct boats. By following the necessary instructions, your hole will disappear after a few hours of work on it.

And if you get your smooth surface right and do a good job with your painting, the repair job will be invisible to someone who has never seen it.

One note of caution though: if the hole in your boat is below the water level, and you have no experience with repairing a fiberglass boat, let a professional do it.

It’s riskier as there is no margin for error. You don’t want your shabbily done job caving in in the middle of the sea. Get a professional to do this for you. But you can attempt anything above the water level yourself.

Don’t let that large hole scare you today, you got it covered.

Recent Posts