To inspect a boat, you must understand how it was built. A solid fiberglass fishing boat fails differently than a cored racing sloop. A surveyor needs to be a material scientist, detecting the specific failure modes associated with each construction method.
1. Solid Fiberglass (FRP)
Most production boats from the 1970s and 80s are solid glass. They are heavy and durable, but not invincible.
Failure Mode: Osmotic Blistering
Water molecules penetrate the gelcoat and react with uncured resins, creating acidic fluid that pushes the gelcoat out.
- Inspection: Look for bumps on the bottom. Pop one (with permission). If it smells like vinegar (acetic acid), it's a blister.
Failure Mode: Hard Spots
Bulkheads tabbed directly to the hull without foam stress-distribution pads create "Hard Spots." As the hull flexes, it pivots on this stiff line, causing stress cracks on the exterior.
2. Cored Construction (Sandwich)
To save weight and increase stiffness, builders sandwich a core (Balsa, Foam, Honeycomb) between two thin skins of fiberglass.
Failure Mode: Core Saturation (Rot)
If deck hardware is installed without sealing the core, water enters. Balsa allows water to migrate (wick), rotting large areas.
- Inspection: Percussion sounding is key. A dull "thud" means the skin has delaminated from the core. A moisture meter will confirm saturation.
Failure Mode: Delamination
Under repeated impact (like pounding into waves), the skin can shear off the core. This catastrophic failure leads to a "soft" hull that flexes dangerously.
3. Wood
Wood is organic. It wants to decompose.
Failure Mode: Galvanic Corrosion of Fasteners
Wooden boats are held together by metal. If the fasteners corrode, the planks spring loose.
- Inspection: Look for "weeping" rust stains at bung holes. This is "nail sickness."
Failure Mode: Dry Rot
Fresh water (rain) trapped in unventilated areas (like the stem or transom) causes fungal decay. Saltwater actually pickles and preserves wood; rainwater kills it.
4. Aluminum
Aluminum is strong and light but susceptible to electrolysis.
Failure Mode: Crevice Corrosion
Aluminum needs oxygen to maintain its protective oxide layer. If you trap efficient water against it (like under a dirty bilge or a teak deck), it corrodes rapidly.
Failure Mode: Pitting
Stray current in a marina can eat an aluminum hull in days. Isolation transformers are mandatory.
5. Steel
Steel rusts. It heals itself (unlike aluminum) but requires constant maintenance.
Failure Mode: Rust Jacking
Rust takes up 7x the volume of steel. If rust forms between two plates, it can rip welds apart with hydraulic force.
Failure Mode: Internal Corrosion
Steel boats usually rot from the inside out. Bilge water sitting against the plating is the enemy. An ultrasonic thickness gauge (Audio Gauge) is mandatory for steel surveys.
Conclusion
When you approach a boat, identify the material first. Adjust your mindset and your tools. You don't hammer-sound a steel boat, and you don't look for rust on a fiberglass one. Tailor your inspection to the material science.