AME Unit 5 Q6

Delamination, the separation of layers in a composite material, is a common issue in GRP hulls. It can be caused by a variety of factors:  

1. Fibreglass boat repair – a solid solution to delamination – Epoxycraft

Manufacturing Defects

• Poor Quality Resin: Low-quality or improperly cured resin can weaken the bond between layers.
• Insufficient Curing: Inadequate curing of the resin can lead to weak bonds and delamination.
• Void Formation: Air bubbles trapped within the laminate can create weak points.
• Incorrect Fiber Orientation: Improper alignment of the fiberglass fibers can reduce the laminate’s strength.

Environmental Factors

• Osmosis: The ingress of water into the laminate can degrade the resin and cause delamination.
• Ultraviolet Radiation: Prolonged exposure to sunlight can degrade the resin, making it more susceptible to damage.
• Temperature Extremes: Frequent exposure to extreme temperatures can cause thermal stress and delamination.

Operational Factors

• Impact Damage: Collisions or groundings can cause significant damage, including delamination.
• Fatigue: Repeated stress from wave action and engine vibration can contribute to delamination.
• Improper Repairs: Poorly executed repairs can weaken the laminate and accelerate delamination.

Understanding these causes is crucial for preventing and addressing delamination issues in GRP hulls.

Osmotic blistering is a common issue in GRP hulls caused by the ingress of water and the presence of salts within the laminate. Here are the primary causes:  

1. Solve Hull Blisters in Boat Paint – Interlux

• Salt Contamination: The presence of salts, such as chlorides and sulfates, on the hull surface before the application of the gel coat can lead to osmotic blistering.
• Water Ingress: Imperfections in the gel coat or laminate, such as pinholes or microcracks, can allow water to penetrate the hull.   1. Survey Issues – Osmosis on a Fisher 25 www.boatsurveyor.net
• Resin Quality: Low-quality or improperly cured resin can have higher permeability, allowing water to infiltrate the laminate.
• Environmental Factors: Exposure to harsh marine environments, including saltwater, high humidity, and temperature fluctuations, can accelerate the osmosis process.

These factors combine to create a concentration gradient, driving water into the laminate and causing the formation of blisters.

Stress cracking in GRP hulls is the formation of cracks due to the repeated application of stresses that exceed the material’s elastic limit. This can lead to progressive damage and eventually structural failure.

Causes of Stress Cracking:

• Flexural Fatigue: Repeated bending of the hull, caused by waves and other external forces, can lead to microscopic cracks that eventually propagate.
• Thermal Stress: Differences in temperature between the hull’s inner and outer layers can cause expansion and contraction, leading to stress and cracking.
• Chemical Attack: Exposure to certain chemicals, such as antifouling paints or cleaning agents, can degrade the resin and weaken the laminate.
• Design Flaws: Stress concentrations caused by sharp corners, inadequate reinforcement, or poor joint design can contribute to stress cracking.   1. Stress Cracks & Surface Irregularities on Boat: “Surveying Fiberglass Power Boats” (2E) by David Pascoe – Chapter 8 www.davidpascoe.com
• Manufacturing Defects: Voids, porosity, or improper curing of the resin can create weak points in the laminate.

Understanding the causes of stress cracking is essential for preventing and addressing the issue effectively.

Osmotic blisters in GRP hulls typically appear in areas that are most exposed to water and where there’s a higher likelihood of water ingress.

• Below the Waterline: This is the most common area for blisters to appear, as it’s constantly submerged and exposed to saltwater.
• Waterline Area: The area just above and below the waterline is also susceptible due to the constant wetting and drying cycles.
• Chain Locker and Anchor Well: These areas are often exposed to saltwater and can be prone to moisture retention.

While blisters can occur anywhere on the hull, these areas are particularly vulnerable due to their constant exposure to water and the potential for water ingress.

The part of the underwater section of the hull on which osmotic blisters most commonly occur is the waterline area.

This is due to the constant exposure to fluctuating water levels, which creates ideal conditions for water ingress and the development of osmotic pressure.