Do-It-Yourself , Centerboard Trunk Repair on Sweet-16

by Sean White, 3/15/00

Last summer I took my first sailing class and in no time was hooked on this wonderful, family-oriented pastime. Before I knew it I was looking around for a used daysailer. After looking at several boats (Snipe - rigging too complex; Buccaneer - too big; Laser - too small), I finally settled on the venerable Sweet 16.

The Problem

What a great all around boat the Sweet is! After a fun-filled summer of daysailing with my wife and kids and Sunday racing with the local sailing club, I noticed one of the centerboard pendant brackets was higher than the other one. After removing the centerboard, I discovered the fiberglass skin on top of the CB trunk had cracked and allowed water to soak the ½ in. plywood underneath causing it to swell and delaminate (photo 1).

Photo 1 - close up of the damage

Removing the Damaged Wood

After getting a good look at the damage, I devised a way to remove old fiberglass and rotten wood using a plunge router. I fashioned a jig by nailing some scrap 1x2 and 1x4 pieces to the top of the trunk to serve as guides for the router (see photo 2). I used a ½ inch wide straight bit and began by setting the cut depth to 1/8 in.. The depth of the bit was adjusted with each subsequent pass until I had removed about 5/16 in. of material (see photo 3). I discovered the core of the CB trunk on the Sweet-16 is made out of green Styrofoam like the kind that florists use to make flower arrangements (obviously one of the weight saving features used by the builder). In order to maintain as much of the original structural integrity, I did not cut all the way through the original plywood with the router into the green foam - about 1/8 in. of the original wood remained after the cut.

Photo 2 - jig used to guide the router

Photo 3 - top of the trunk after removal of the damaged plywood

Selecting Materials for the Repair

Having never done any boat repair work, I looked through an issue of Wooden Boat magazine and found an ad for a trial kit of epoxy resin from System Three Resins (P.O. Box 70436, Seattle, WA 98107, 800-333-5514). The System Three trial kit cost $10 and included THE EPOXY BOOK, 12 ounces of resin and hardener, fiberglass cloth, brushes, measuring cups, fillers, roller cover, squeegee and gloves (Photo 4). The System Three trial kit is very impressive and includes enough materials to give the boat repair novice a really good, "hands on" understanding of how epoxy resins work - especially the 50-page book on how to use epoxy resins in boat building and repair. What a deal for $10 plus shipping and handling!

Photo 4 - the System Three trial kit

Next, I cut a scrap piece of wood (a dry piece of pressure treated 1x2) to approximately fit the area. The 1x2 fit snugly lengthwise into the cut, but was about ¼ in. narrower than the wood I removed (more on this later). In addition to the new wood for the top of the CB trunk, I also drilled out the old screw holes and inserted 3-in. lengths of hardwood dowel down into the green styrofoam to make a better substrate for anchoring the CB pendant brackets. The piece of wood and hardwood dowels were glued in with epoxy (photo 5).

Photo 5 - gluing in the hardwood dowels and replacement wood

The reason I used the smaller-than-optimal 1x2 was because I didn't have a table saw to rip a piece the exact width and I wanted to experiment with the epoxy trial kit filler materials. Since the wood was narrower than the section I removed, I filled the gap with an epoxy/silica/plastic fiber fillet cooked up with the System Three trial kit (photo 6). After gluing the 1x2 and filling the gap with the fillet material, I coated the entire repair area with more epoxy resin and a layer of fiberglass cloth included with the kit.

Photo 6 - the repaired area after glassing (the white strip on the outboard edge of the trunk is the epoxy fillet)

Finishing the Repair

One critical step to boat repair using epoxy resin is protecting the repair from the sun - epoxy exposed to sunlight must be protected from degradation by ultraviolet (UV) light. After the epoxy cured I sanded the surfaces smooth and applied three coats of oil-based, alkyd enamel primer, followed by an oil-based, alkyd enamel top coat that matched the original interior color (photo 7). Once the primer and top coats dried, I attempted to replicate the original "splatter" finish by dipping the tip of my paint brush in the paint and flinging the color onto the repaired area. This technique worked after a fashion, but I ended up with yellow paint specks all over the place (the garage ceiling, my face, the cat, etc.). In the end, the CB trunk repair looked pretty good and should last for several more seasons - see Photo 8.

Photo 7 - protecting the repair from UV with a several coats of primer

Photo 8 - even "Fremont" is impressed with the CB trunk repair!