Hull and laminate

The hull shell keeps the sea out and carries rig, keel, rudder and machinery loads. A solid laminate is layers of fiberglass reinforcement in resin. A cored laminate sandwiches balsa, foam or another light core between inner and outer fiberglass skins; separating a skin from the core is delamination. Internal floors, stringers and bulkheads distribute loads. Tabbing is the fiberglass tape bonding those structures to the hull. Gelcoat is the thin cosmetic/water-resistant outer finish, not the primary structure.

Moisture-meter readings are comparative clues, not direct percentages of water. Antifouling, metal, carbon, salts and recent haul-out affect them. Osmotic blisters are fluid-filled gelcoat/laminate defects; they range from cosmetic surface work to deeper hydrolysis. A crack's location, direction and movement matter more than its appearance.

Structural laminate failure can allow flooding or change how keel, rig and rudder loads enter the boat. Debonded bulkheads and floors let the hull flex. Prior grounding may crack floors or laminate well away from a visible keel scar. Widespread wet core increases weight and can destroy fastener holding. Cosmetic crazing is usually tolerable; a cracked structural load path is not.

First stop the water source or load causing damage. Small solid-laminate damage is ground back to sound material and rebuilt with correctly oriented glass/resin. Cored repair requires removing damaged skin/core, drying or replacing core, rebonding and restoring laminate. Injecting resin into a wet, rotten core is not automatically an adequate structural repair.

Blisters may be monitored, locally repaired or—when widespread/deep—peeled/dried/barrier-coated. Bulkhead or floor tabbing is repaired to an engineered schedule with clean access and correct taper. Whole-hull replacement is not a normal option; major structural defects affect whether to buy the boat at all.

• Covered by a standard survey — visual/percussion examination of accessible hull, moisture-meter sampling, cracks/blisters, visible repairs, accessible tabbing/stringers/floors and haul-out inspection. A good survey records a pattern, instrument and conditions, not a single magic moisture number.
• Not covered — removing liners, drilling/core samples, destructive testing, ultrasound/thermography, laminate engineering and hidden repair verification. Focused non-destructive testing may cost $500–$2,000; destructive samples and naval-architect/composite review more. Do it before purchase when there is a broad anomalous map, flex, unexplained repair, impact or cracked load path.

• The broker or owner — “Send every grounding/collision/insurance claim and structural repair invoice, including photos before, during and after repair and laminate schedule.” “Identify hull laminate/core by area from builder documentation.” “Has water entered floors, stringers or core, and how was it proven dry?”
• The surveyor — “Map rather than spot-check moisture and percussion; identify instruments/conditions; inspect floors, stringers, bulkhead tabbing and known model load paths; distinguish cosmetic gelcoat from structural laminate; and recommend destructive or specialist testing only where evidence supports it.”

Sight along the hull in low-angle light for unfair patches. Tap gently with a plastic screwdriver handle and listen for a change from crisp to dull; this is comparative, not a verdict. Inside, use a bright light around floors and bulkheads for separated tabbing edges, white stress fibers, cracks that continue through structure, water trails and fresh paint hiding one area. Push on suspicious panels while someone watches the opposite skin. At haul-out, inspect the keel zone, rudder area and sling points first.