Drilling & Repairing Fiberglass

Learn the essential steps for drilling into fiberglass on your boat, whether installing equipment or making repairs.

A Few Steps That Should Be Followed

Fiberglass is light and it is durable — two important components for boat building. While many of the new models you will read about are made up of composites and use new design technologies, it is still basically a fiberglass boat that comes off the assembly line. Chances are good that you are going to have to drill a hole or two in this time-tested material when installing a new GPS or make a minor repair after a day when docking the boat didn’t go as planned. It is doable, despite the initial fears of every fiberglass first-timer. After all, boats aren’t supposed to have holes in them.

But drilling a hole goes with the territory. Literally.

And it’s relatively painless for the boat owner if some care is taken with the drill. BoatUS Trailering Magazine asked Bud Eiden, president of Ongaro Marine Representatives for some pointers when the drill is aimed at the fiberglass.

Step 1 – Before you do anything, check to see what is behind where the drill is going to go. Eiden says there are too many stories from backyards where someone has drilled through the fiberglass into a fuel line, hydraulic line or electrical cables.

Step 2 – If you are installing load-bearing hardware, it is essential you use a backing plate. This ensures a strong holding capacity. If your boat is a newer model, you’ll find the fiberglass is actually thinner as a result of the composites used in the materials. This fact alone will require the use of a backing plate even if the hardware isn’t going to be stressed. If there isn’t enough room for a backing plate you are going to have to rethink where that load-bearing hardware should be placed.

Step 3 – Boats vibrate. As a result, thru-bolting is the preferred technique (a bolt is placed through the fiberglass and into a wooden or metal backing plate and secured with a nut and washer). Consider using nylon locking nuts with washers for optimal fastening on backing plates.

Step 4 – Know the size of the hole you need to make in the fiberglass. Your new component probably comes with bolts or screws for installation. Installation instructions often provide the hole size required for mounting. Use a drill bit one size smaller to drill a “pilot hole”. It is usually a good idea to make a small indentation in the spot where you want the hole before any drilling is done. This prevents the drill from wandering. Go slow and let the drill do the work. When complete, use the next size drill bit until you have made a hole into which the bolt/screw is going to fit.

Step 5 – Use a countersink bit to make an indentation in the hole. This allows the bolt/screw to be level on the surface (assuming it’s designed to be countersunk) while also eliminating stress on the gelcoat that can result in surface cracks.

Step 6 – If the hole you need to make is larger than half an inch, forget using the drill altogether and instead use a round or hole saw.

Step 7 – If you need to make a hole perpendicular to the surface (usually used when installing load bearing hardware like blocks or hatch cover hinges) consider using a drill guide alignment tool to ensure the hole is properly drilled.

Step 8 – Be sure to bed all fasteners above the waterline with a marine grade silicone sealant. Below the waterline, bed all fittings with a polysulfide sealant such as 3M’s Marine 101 (and if the bond is to last as long as you own the boat, 3M’s 5200 or a similar product is the preferred choice).

Cosmetic Fiberglass Repairs

While fiberglass is a tough material, it’s going to get whacked from time to time, regardless of the skipper’s competence and ability. And some of those times may require a Saturday afternoon for repairs. The good news is working with fiberglass has become easier through the years. The bad news is, despite the simplicity, it’s still going to cost you a Saturday afternoon.

“Fiberglass repair is a broad subject area,” says Eiden, “and the beginner needs to understand a few of the basics. Following the directions supplied with gelcoat repair products and taking time with the repair can easily complete most cosmetic repairs to the gelcoat. For gelcoat repairs, always use polyester products that will be compatible with the area to be repaired. Epoxy resins are an excellent repair material but should not be used in gelcoat repair (it is used most often on repairs below the waterline). On the hull or deck, you’ll want to work with one of the many polyesters that are available.” Eiden cautions, however, if the hole in the boat is more serious than just a cosmetic repair job and you aren’t familiar with using polyesters, swallow your pride and have a professional do the work.

The way to choose what product to use is to look at what has to be repaired. “It depends on how deep a gouge or knick you have on the boat,” Eiden says, “but you’re going to have to take a close look at it.”

Step 1 – Preparing the surface for the repair is a very important step. All loose material should be removed. Then, a sanding of the repair area with a 220 grit sandpaper to remove dirt and oils should be done. Follow this with an acetone wash to remove any remaining oil, wax or dirt that may remain after the sanding process.

If you have a deep gouge (but not into the laminates), fill the area with a marine grade reinforced polyester filler such as “Formula 27”. After the filler has cured (about one hour in 60 degree temperature), sand the filler down to about 1/8″ below the surrounding gelcoat surface level. This 1/8″ depression will “hold” the gelcoat or gelpaste repair patch.

Again, wash the repair with acetone to prepare it for your gelcoat product.

Step 2 – Selecting the type of gelcoat for the repair is important. There are two options available to you: Gel Paste or Gelcoat. Gelcoat is the same material that the boat builder used in the construction of your boat. It is a paint-like liquid that requires an MEKP hardener that is supplied with the gelcoat. Gel Paste is a semi-clear, thickened gelcoat that has the consistency of Vaseline. It too requires MEKP hardener to become activated to harden. Gel Paste is available in convenient kits that include hardeners, tinting agents, mixing cups and detailed instructions. These kits are ideal for small jobs and can be reused if you run into another repair later on in the season.

Step 3 – You will most likely have to tint your gelcoat or gelpaste to match your boat’s gelcoat color. This is done by adding tinting agents (pigments) available from the gelcoat manufacturer. You should always do your color matching prior to activating the gelcoat with MEKP. Try to match the color a shade darker than the gelcoat on you boat as it will fade over time and more closely match the boat’s color. If you are determined to exactly match you gelcoat, contact the boat’s manufacturer. Most will sell you a quart of the original gelcoat (providing they have not changed to a new color gelcoat in their boat production.)

Step 4 – Gelcoat will need to be sprayed or brushed onto the repair. Tape around the area being repaired to avoid “overspray” and aid in easy clean up. Gelpaste can be applied with a plastic spreader or flexible putty knife. Generally speaking, Gelpaste is ideal for small gouges and knicks. Its putty-like consistence is easy to work with and to apply. Gelcoat is best suited for larger repairs where spraying or brushing on will save you time and provide excellent results. Apply the Gelcoat or Gel Paste slightly above the surface of the surrounding Gelcoat to allow for finishing.

Step 5 – Gelcoat and Gel Paste will cure to the touch in about an hour; however, give it a couple of hours time to ensure full curing under the surface. Finish the repair with a wet-sanding using 600 grit sandpaper (or higher) until the repair surface is level with the surrounding area. Compound the area with a light duty compound until all sanding marks are eliminated. Finish with a premium marine wax.

Remember to always follow the manufacturer’s recommendations and take your time in doing the repairs. Of course, protective equipment such as gloves, eye protection and dust masks are always recommended.

BoatUS Editors

Contributing Editor, BoatUS Magazine

About Vessel Vanguard

Vessel Vanguard is a leading marine safety and maintenance management software provider dedicated to revolutionizing the maritime industry. With a commitment to innovation and excellence, Vessel Vanguard delivers cutting-edge solutions to streamline operations and enhance vessel performance and safety.

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