How To: TRADE SECRET: Fibreglass boat repair – replacing stringers
29th May 2015

Fibreglass boats are known for their low maintenance and durability. However, with structural damage to the stringers a common issue, it’s essential to know how to make a replacement that will last.

Although fibreglass boats tend to require less maintenance than their wooden counterparts, they’re not without problems. They suffer from many of the same age-related problems of fatigue and moisture experienced by traditional wooden boats, as well as the usual damage from collisions, groundings and the forces of nature.

Making sure your boat stringers are healthy and strong is an essential part of fibreglass boat maintenance. Although it’s possible to replace small sections of the stringer, it’s often easier to make a full replacement which ensures there is no remaining damage left below the deck.

To replace your stringers, follow this simple seven-step method:

Prepare the surfaces
All surfaces should be clean, dry and sanded. Remove any traces of contamination by wiping the surface and drying with paper towels.
Mark the area
Before removing the damaged stringer, mark out its position so you can make sure you put the replacement in the same place. It’s a good idea to mark these in away from the repair area so they will not be disturbed when the surface is prepared prior to bonding.
Remove the damaged stringer
Remove the stringer and core. Use a grinder to cut the tabbing at the core/hull joint but be sure not to cut into the hull laminate. Measure the thickness of the fibreglass skin so that it can be duplicated.
Make the core
Using the same type of wood as the existing core, cut a piece of the timber to fit the size and shape of the core in the removed stringer. Dry fit and trim the new piece for a good fit.
Sand the surfaces
Abrade the bonding surfaces by sanding with 50-grit paper and brush the area free of dust or loose material. Sand the bonding surfaces of hardwood or epoxy coated stringers with 50-grit sandpaper.
Bond the core
With a resin/hardener mix, wet out all contact surfaces of the hull and core. Apply a liberal amount of thickened epoxy/404 High-Density or 406 Colloidal Silica mixture to one side of the contact area. Push the stringer in position with firm hand pressure. Thickened epoxy should squeeze out of the joint. Shape the squeezed out epoxy into a fillet and if necessary apply additional thickened epoxy to the joint for a smooth 12mm radius fillet. Make sure you clean up any excess epoxy before it cures.
Finishing
Now you have successfully replaced the stringer, all that’s left to do is replace the fibreglass skin and your deck will, once again, be fully supported.