Ask SAIL: Repairing Deep Gouges

Author:
Don Casey
Updated:
Oct 27, 2022
Original:
Feb 26, 2016

The exact type of repair in a situation like this one depends on the depth of the damage

DEEP GOUGES

Q: While on a night passage aboard my boat, I struck an unidentified floating object. It did not penetrate the inner laminate, but left a couple of deep 6in-long gouges in the hull. I have a rather large damage excess on my insurance policy and would like to attempt the repair myself, as I have some experience with using epoxy resin. What is the procedure for repairing such damage?

Fred Johnson, via sailmail@sailmagazine.com

DON CASEY REPLIES

Gouge repair is not difficult, but you will need to assure yourself that flexing from the impact did not force the inelastic layers of glass to slide across each other, shearing the bond between them and causing delamination. The test for this is to tap the area with a plastic mallet or the plastic handle of a screwdriver. A sharp report suggests solid laminate. A dull thud merits further investigation. A modest gouge—let’s call it a wide scratch—can simply be filled with an epoxy putty or even with gelcoat if the damage is above the waterline. Preparation is just sanding. Finish is sanding then polishing for topsides, or painting for underwater. If the damage is more serious—the gouge has torn through some of the glass fabric—you will need to reinforce your repair with new fabric to restore full integrity, and to do this your patch needs to be scarfed in place. This is done by grinding away the edges of the gouge to convert it into a gentle depression. The rule of thumb is a 12-to-1 chamfer all around. If the gouge is, say, ⅜in deep, the chamfer on each side needs to be 12 times ⅜in, or 4½in, on both sides of the gouge, so the total repair width is around 9in. Chamfer the ends the same way. Because you are doing the repair with epoxy, you can make all of your laminates from fiberglass cloth, starting with a piece big enough to cover the entire repair area, then adding sequentially smaller pieces until the repair is almost level with the surrounding area. Laying the cloth in a large-to-small sequence maximizes the secondary bond between the patch and the hull. There are lots of written instructions available, including in several of my own books. West System also provides its excellent Fiberglass Boat Repair & Maintenance Manual for free online, which instructs on epoxy use in addition to repair guidance.