Fiberglass (FRP) is an amazing material. It is strong, rot-proof, and shapeable. But it is not fatigue-proof. Over decades of slamming into waves, tightening rig tension, and grounding on hardened mud, fiberglass structures begin to fail.
As a surveyor, you must distinguish between cosmetic aging (thermal crazing, star crazing) and structural distress that threatens the vessel's integrity.
1. The Language of Cracks
Gelcoat is brittle; fiberglass laminate is flexible. When the laminate flexes beyond the gelcoat's elastic limit, the gelcoat cracks. The pattern of the crack tells you the force vector.
Parallel Stress Cracks
Appearance: A series of parallel lines, often on the cabintop or deck beams.
Diagnosis: Bending. The underlying beam is flexing under load (e.g., a mast step pushing down). The cracks run perpendicular to the stress.
Radial Cracks ("Spider Webs")
Appearance: Cracks radiating outward from a center point.
Diagnosis: Impact or Point Loading.
- Impact: Dropping a winch handle creates a generic spider crack. Low concern.
- Point Load: A stanchion base pulled upwards by a lifeline creates a "tenting" spider crack. This indicates a lack of proper backing plate.
45-Degree Cracks (Shear)
Appearance: Cracks running at 45 degree angles at the corners of window cutouts or bulkheads.
Diagnosis: Torsional twisting. The hull is twisting in a seaway, and the square corners of the window are stress risers. This is common in production boats but indicates structural movement.
2. Tabbing Separation
The hull is a shell; the bulkheads are the skeleton. They are glued together with fiberglass tape ("tabbing"). If this glue fails, the boat loses rigidity.
Where to Look:
- Chainplates: These pull the hull up. Check the main bulkhead tabbing. If you see white powdery dust or peeled tape, the rig is pulling the bulkhead loose.
- V-Berth: Under the bunk, where the hull slams into waves. Look for tabbing that has cracked away from the hull.
3. The "Hard Spot"
A hard spot occurs when a rigid internal structure (like a bulkhead) pushes against the flexible hull skin without a cushioning foam pad.
The Symptom:
View the hull from the outside, looking down the gloss reflection. If you see a vertical crease or a line of stress cracks that matches the interior bulkhead location, you have a hard spot. Over time, this hinge point can crack the laminate.
4. Keel Stubs and Garboards
Groundings are common. Proper repairs are rare.
The "Smile":
A crack at the forward end of the keel-to-stub joint. It means the keel hit something and was leveraged down at the back, pulling the front open.
The "Frown":
A crack at the aft end. Often from the boat sitting on its keel on the hard without proper hull support, crushing the aft joint up.
Conclusion
Structural surveying is detective work. You are looking for the evidence of invisible forces. When you see a crack, ask "Why?" What force created this? Is the structure sufficient to handle that force? If the answer is no, it's a Recommendation.