What material is best for boat trailer bunks?
The carpet on my trailer bunks is worn through and one board feels soft around the bolts. Should I replace them with treated timber and new carpet, or would plastic bunks last longer without damaging the hull?
Answer
For most fibreglass boats, the best all-round trailer bunk is straight structural timber in sound condition, covered with purpose-made marine bunk carpet. For aluminium boats, avoid direct contact with copper-treated timber and choose a hull-compatible covering or a purpose-made bunk system approved for the boat's weight.
Check the boards and support
Check the boards around their mounting bolts, then look at where the bunks touch the hull. Replace rotten timber, but check the positioning too. Even a sound board can damage a boat if narrow contact patches concentrate the load.
With the boat safely off the trailer, push a screwdriver into suspect areas around bolt holes and beneath the carpet. Soft fibres, deep splits, crushed mounting holes or permanent sagging mean the board needs replacing. Inspect brackets, swivel plates and fasteners at the same time.
If you must work beneath the boat, support it on properly rated stands or lifting equipment, never on a jack alone.
Copy the original bunk length, section, orientation and bracket spacing unless the boat or trailer manufacturer specifies a change. Many small-boat trailers use nominal 2 × 4 or 2 × 6 boards; actual finished dimensions vary between suppliers and countries. A wider board does not automatically carry more weight if only one edge touches the hull.
Timber and carpet
Choose straight structural softwood with few knots, particularly around mounting points. Pressure-treated pine suits many fibreglass boats, provided the treatment can withstand repeated wetting and the fasteners are compatible with it. Ordinary untreated softwood costs less initially but is more vulnerable to decay beneath damp carpet.
Timber is affordable and easy to drill, with enough flex to follow a curved hull. Dense hardwood is not automatically better. Extra stiffness can stop a bunk following the hull properly, and some species split readily around fixings.
- Covering: use marine bunk carpet intended for repeated immersion, with a backing that drains rather than holds water against the board.
- Edges: round sharp corners and smooth the loading end before fitting the covering.
- Fixings: keep staples, screw heads and carpet seams away from the hull contact surface.
- Maintenance: rinse away salt and grit, and inspect beneath loose or damaged carpet.
Carpet protects gelcoat and provides useful friction during launching. It also traps grit, retains moisture and conceals rot. Replace it before the backing wears through and exposes timber or metal.