Dinghies are the poor stepchildren of the boating world. They are overworked, underappreciated and mistreated by their owners, who lavish all their attention and money on the "big boat." Yet dinghies are entrusted with precious cargo every time they taxi our families and friends to and fro in spite of the boats' increasingly dilapidated condition. Developing fibreglass repair and hull painting skills ought to be a priority for all boat owners not only for safety concerns, but also because of the high cost of replacing a boat that has failed due to misuse and neglect.
Wash the hull with detergent and water to remove dirt and wax residue. Cracks in the fibreglass should be scraped out with a sharp pointed object such as a nail or a flathead screwdriver. Use a hair dryer to dry out any moisture accumulated in the deeper cracks, Open a small can of pure epoxy resin and another of liquid hardener. Load a small paintbrush with equal portions from each can and wet each crack. Wetting diminishes surface tension and improves chemical bonding so the epoxy filler applied next will fill in the cracks and chemically adhere to the old finish.
Add a high fibre crack filler and epoxy mix that can be found at any marine store. Mix it to the consistency of peanut butter and with enough hardener to permit at least 15 minutes of application before the hardener activates. Instructions on the appropriate mix of epoxy and hardener are on the can. Using a trowel, fill in all the pretreated cracks and dings, remove excess and clean up any remaining spillage with an acetone solvent. Let dry for 24 hours, then use a palm electric sander with 80 grit sandpaper to smooth the treated surfaces. Resand with 220 grit sandpaper and thoroughly wash the hull down with fresh water to remove all dust.
Apply two epoxy primer coats, wet sanding in between each application using 220 grit sandpaper. This will cover up all spider cracks and crazing in the outer layer, high-gloss resin finish -- known as the gelcoat -- and prepare the fibreglass for painting. Remember to put on your protective glasses, respirator and gloves before painting. Your local marine store can help you pick out a suitable single-coat or more durable two-part polyurethane paint, both of which can be applied with a roller or paintbrush. The secret of a good paint job is the preparation of the undersurface before application. So, do the job right and put a shiny smile back on the face of your faithful little dinghy.
Repairs should be conducted outside or in a well-ventilated enclosure. Wear safety glasses, respirator or dust mask, and neoprene disposable gloves whenever working around epoxy, polyurethane, solvents or sanding dust. Never smoke or operate an open flame device such as a blowtorch near the repair site.