Winter often feels like a dormant period for boating enthusiasts. The vessel is wrapped, the engine is fogged, and the batteries are on a trickle charger. While it is tempting to ignore your boat until the first thaw, the colder months offer a strategic advantage for hull and transom maintenance.

Addressing small fiberglass repairs now saves you from the frantic rush of spring commissioning. More importantly, it prevents minor cosmetic issues from evolving into significant structural problems. Water intrusion, osmosis blisters, and delamination often start as small chips or cracks that went unnoticed or ignored. By utilizing the offseason, you ensure your boat is not only seaworthy but pristine when launch day finally arrives.

Why Tackle Fiberglass Now?

Fiberglass work requires patience and time—two luxuries you rarely have in the spring when the weather turns warm and the urge to get on the water is overwhelming.

Winter provides the necessary downtime for repairs to cure properly without the pressure of a looming weekend trip. Additionally, fiberglass hulls benefit from drying out over several months. If you have any deep gouges that have absorbed moisture, the dry winter air helps wick that moisture away before you seal it back up.

However, temperature is a critical factor. Most resins and gelcoats require temperatures above 70°F (15°C) to cure correctly. If you are working in an unheated garage or boatyard, you may need to utilize space heaters or heat lamps to create a localized warm zone for your repairs.

Inspecting the Hull and Transom

Before mixing any resin, you need a comprehensive map of the damage. Grab a roll of blue painter's tape and a bright inspection light, then slowly walk the perimeter of the boat.

Transom Stress Cracks

The transom takes a beating, especially on powerboats with outboard motors. Look closely at the upper corners of the transom and around engine mounting bolts. You are looking for spiderweb cracks or hairline fractures.

While fine spiderwebbing is often cosmetic (restricted to the gelcoat), deeper cracks that open and close when the motor is tilted suggest structural flex. These require special attention. For this guide, we are focusing on the cosmetic cracks and chips that are not as difficult to fix.

Keel and Strakes

Get low and examine the very bottom of the hull. The keel often impacts submerged objects, trailers, or sandbars. Check for gouges that have penetrated through the shiny gelcoat and exposed the raw, fibrous fiberglass mat underneath. These are high-priority fixes, as exposed fiberglass acts like a sponge.

Dock Rash and Topside Dings

Inspect the rub rail and the hull sides. This is where dock pilings and fenders leave their mark. Look for chips where the gelcoat has flaked away, leaving a crater. These are usually easy to fill but unsightly if left alone.

A Step-by-Step Guide to Small Fiberglass Repairs

Once you have marked your repair zones with blue tape, it is time to gather your materials. For small cosmetic repairs, you will typically need:

• Acetone and clean rags
• Dremel tool or sandpaper (80-grit to 600-grit)
• Resin with filler
• Gelcoat if not working with epoxy resin. Gelcoat will not adhere to epoxy resin.
• Plastic spreaders
• PVA (polyvinyl alcohol) or wax paper

Step 1: Preparation and Grinding

A successful fiberglass repair relies entirely on adhesion. You cannot simply smear filler over a crack; it will pop out within a month.

Start by cleaning the area thoroughly with acetone to remove any wax, grease, or contaminants. Next, use a Dremel tool or a sanding block with 80-grit paper to open up the crack or chip. You want to create a "V" shape. This beveling increases the surface area for the new material to bond to and eliminates sharp edges that cause stress risers.

After grinding, vacuum the dust and wipe the area down with acetone again.

Step 2: Filling the Void

If the gouge is deep (into the fiberglass laminate), use a structural filler/ putty. Marine-grade epoxy resin with fillers are excellent for this as they are strong and waterproof. Vinyl ester resin with fillers are also a great choice

If you are not purchasing a premade putty, mix the filler according to the manufacturer's ratio with the resin of choice. Using a plastic spreader, press the putty firmly into the void to eliminate air bubbles, then smooth it out. Leave the putty slightly lower than the surrounding gelcoat to leave room for the final finish layer.

If you are working in a cold environment, this is where your heat lamp comes in. Keep the area warm (but not hot) to aid the curing process.

Step 3: Sanding the Filler

Once the putty is hard, sand it smooth with 120-grit paper. You want a level surface that transitions seamlessly into the surrounding hull, but sits just a fraction of a millimeter below the final surface level. Clean the dust away with acetone.

Step 4: Applying Gelcoat

This is the cosmetic layer that restores the shiny, white (or colored) finish. Unwaxed gelcoat does not cure in air; it remains tacky so additional layers can be added without the need for sanding. To get it to harden tack free on the final coat, you need to add a sanding aid (wax additive) or use a waxed gelcoat. You can also cover the final layer of the repair with PVA or a piece of wax paper to starve it of oxygen.

Mix your gelcoat paste with the hardener. If you are color-matching, this is the time to be precise. Overfill the repair slightly, as gelcoat shrinks when it cures. If you aren't using a waxed gelcoat or wax additive, tape a piece of wax paper over the wet gelcoat to seal it.

**Do not use gelcoat if working with epoxy resin.

Step 5: The Final Polish

After the gelcoat has fully cured, remove the wax paper. You will likely have a small bump where you overfilled.

1. Sand: Start with 220-grit wet-dry sandpaper (wet) and sand the bump flush with the hull. Be careful not to sand through the surrounding original gelcoat.

2. Refine: Move to 400-grit, then 600-grit, and finally 1000-grit wet sandpaper. By the time you finish with 1000-grit, the repair should be smooth and dull.

3. Buff: Use a rubbing compound and a wool pad on a buffer to bring back the shine. Finish with a high-quality marine wax to seal the repair.

Check Your Hull Fittings

While you are focused on the fiberglass, check the "jewelry" attached to the hull and transom. Through-hull fittings, scuppers, and drain plugs are common leak points.

Winter is the perfect time to remove, clean, and re-bed these fittings. If a fitting looks corroded or the sealant around it is dry and cracking, unscrew it. Clean the old sealant off both the fitting and the fiberglass. Apply a fresh bead of marine sealant and reinstall. This simple step keeps your bilge dry and prevents rot in the transom core.

Ready for the Water

Handling these small repairs during the winter changes the trajectory of your spring. Instead of spending your first warm weekends covered in fiberglass dust, you will be waxing a smooth, pristine hull, ready to drop into the water.

Take the time now to inspect, grind, fill, and polish. Your boat will look newer, its value will be maintained, and you will have peace of mind knowing the hull is sealed and secure against the elements.