AME 5 Q5

Correct Answer:

A. Sharp corners or edges in the hull design, excessive weight concentration in specific areas, and insufficient reinforcement in high-stress zones.

• Explanation:
  1. Sharp corners or edges: In GRP hull design, sharp corners and edges create stress concentrations where the material is more likely to crack under pressure or stress. The stress is not evenly distributed, leading to potential cracking at these points.
  2. Excessive weight concentration in specific areas: Concentrating too much weight in one area of the hull can create localized stress that exceeds the material’s strength, leading to stress cracking. Proper weight distribution is crucial to prevent such issues.
  3. Insufficient reinforcement in high-stress zones: Areas of the hull that experience high stress, such as around fittings or at points of impact, require additional reinforcement. Lack of reinforcement in these zones can cause the material to fail and crack under stress.

Incorrect Answers:

B. Use of low-quality resin, over-thickness of the gelcoat layer, and high ambient temperatures during construction.

• Why it's incorrect:
  1. Low-quality resin: While the use of low-quality resin can affect the durability and strength of the GRP laminate, it is more likely to result in overall weakness or failure rather than specifically causing stress cracking.
  2. Over-thickness of the gelcoat layer: Excessive gelcoat thickness can lead to issues such as cracking, but it is generally more associated with surface cracking rather than stress cracking due to design flaws.
  3. High ambient temperatures during construction: High temperatures can affect curing but are not a direct design problem that leads to stress cracking. This factor is more related to the construction process than design.

C. Poor paint adhesion, incorrect application of anti-fouling coatings, and improper cleaning methods.

• Why it's incorrect:
  1. Poor paint adhesion: Poor adhesion can lead to paint problems but does not directly cause stress cracking in the laminate.
  2. Incorrect application of anti-fouling coatings: This issue affects the coating layer and not the structural integrity of the GRP laminate.
  3. Improper cleaning methods: Cleaning methods impact the surface appearance and maintenance but are not design issues that cause stress cracking.

D. Excessive use of adhesive sealants, inadequate hull ventilation, and frequent washing with abrasive cleaners.

• Why it's incorrect:
  1. Excessive use of adhesive sealants: While sealants are important for sealing joints, excessive use does not lead to stress cracking in the laminate itself.
  2. Inadequate hull ventilation: This issue affects moisture control and potentially leads to mold or delamination but is not a direct cause of stress cracking.
  3. Frequent washing with abrasive cleaners: This can damage the surface but does not directly lead to stress cracking caused by design issues.

C. Cut out the delaminated section, fill the cavity with a core material, and then cover with a new layer of laminate.

• Explanation:
  1. Cut out the delaminated section: Removing the delaminated or damaged area ensures that all compromised material is eliminated, providing a clean surface for repair.
  2. Fill the cavity with a core material: In sandwich construction, the core material (like foam or balsa) provides structural integrity. Replacing the core material restores the strength and rigidity of the hull.
  3. Cover with a new layer of laminate: Applying a new layer of laminate over the repaired area integrates it back into the hull’s structure, reinforcing the repair and restoring the original strength.

Incorrect Answers:

A. Remove the damaged area, inject resin into the void, and then apply a new layer of fiberglass cloth over the repair.

• Why it's incorrect:
  1. Injecting resin into the void: While injecting resin can be effective for repairing small voids or blisters, it is not suitable for extensive delamination. In sandwich construction, merely injecting resin does not address the missing or damaged core material.
  2. Applying a new layer of fiberglass cloth: This approach does not replace the core material, which is crucial in sandwich construction. The structural integrity of the hull relies on the core material in addition to the laminate layers.

B. Sand the affected area, apply a primer coat, and then repaint the hull to seal the surface.

• Why it's incorrect:
  1. Sanding and repainting: This method only addresses surface issues and does not repair the internal delamination or restore the structural integrity of the hull. It is a cosmetic fix rather than a structural repair.

D. Drill holes into the delaminated area to allow moisture to escape, then apply a sealant and repaint the hull.

• Why it's incorrect:
  1. Drilling holes and applying sealant: This approach is more appropriate for addressing blisters rather than delamination. Drilling and sealing do not repair the internal structural damage caused by delamination. Like option B, this method is a superficial fix and does not address the core material or structural integrity of the hull.

Correct Answer:

A. Tapping the hull with a metal hammer to listen for changes in sound and using a moisture meter to measure the moisture content.

• Explanation:
  1. Tapping the hull with a metal hammer: This technique, known as "sounding," involves tapping the hull with a hammer to listen for changes in sound. A solid, healthy hull will produce a consistent, clear sound, whereas areas with delamination may produce a dull or hollow sound. This method helps identify areas where the laminate may be separating.
  2. Using a moisture meter: Moisture meters are effective tools for detecting the presence of moisture within the laminate. High moisture readings in specific areas can indicate that water has penetrated the laminate and is contributing to delamination. This method helps locate areas where moisture may have caused structural issues.

Incorrect Answers:

B. Inspecting for surface cracks and applying a UV light to detect underlying damage.

• Why it's incorrect:
  1. Inspecting for surface cracks: While surface cracks can indicate problems, they do not specifically detect delamination. Delamination occurs internally within the laminate and may not always be visible on the surface.
  2. Applying a UV light: UV light is typically used to detect issues with cured resins or surface coatings, but it is not effective for detecting internal delamination or moisture content.

C. Conducting a visual inspection for color changes and using a thermal camera to detect temperature variations.

• Why it's incorrect:
  1. Visual inspection for color changes: Color changes on the surface might indicate cosmetic issues but do not reliably detect internal delamination. Delamination often occurs beneath the surface and may not cause visible color changes.
  2. Using a thermal camera: Thermal cameras detect temperature variations and are useful for identifying heat-related issues, but they are not typically effective for detecting internal delamination or moisture within the laminate.

D. Measuring the thickness of the hull with a caliper and checking for vibrations when the hull is exposed to high winds.

• Why it's incorrect:
  1. Measuring hull thickness with a caliper: Thickness measurements may not reveal internal delamination since the outer thickness might remain unchanged even if there is separation between layers inside.
  2. Checking for vibrations in high winds: Vibrations caused by wind do not provide information about internal delamination. Delamination is better detected through methods that reveal internal damage or moisture, such as tapping and moisture meters.

Correct Answer:

A. Excessive moisture ingress, poor adhesion between laminate layers, and impact damage.

• Explanation:
  1. Excessive moisture ingress: Moisture can penetrate the GRP laminate, leading to osmotic blistering. The pressure from the trapped moisture can cause the laminate layers to separate, resulting in delamination.
  2. Poor adhesion between laminate layers: If the resin used in the laminate does not properly bond with the fiberglass layers, it can result in weak spots. These weak areas are prone to separating under stress or pressure, leading to delamination.
  3. Impact damage: Physical impacts can cause cracks and damage to the GRP laminate. This damage can compromise the bond between layers, leading to delamination.

Incorrect Answers:

B. Overexposure to sunlight, improper curing of resin, and mechanical stress during fabrication.

• Why it's incorrect:
  1. Overexposure to sunlight: While UV damage can degrade the gelcoat and resin surface, it is not a direct cause of delamination. Sunlight can lead to surface degradation but does not typically cause the laminate layers to separate internally.
  2. Improper curing of resin: While improper curing can lead to weak bonds, it's not as direct a cause of delamination as poor adhesion between laminate layers. Curing issues more commonly result in surface defects or weak spots rather than full-scale delamination.
  3. Mechanical stress during fabrication: Mechanical stress during fabrication might affect the final product, but it is less likely to be a direct cause of delamination compared to factors like moisture ingress or impact damage.

C. Inadequate paint application, high temperatures during service, and contamination during manufacturing.

• Why it's incorrect:
  1. Inadequate paint application: Poor paint application affects only the outer surface of the hull. It doesn’t directly cause delamination of the internal laminate layers.
  2. High temperatures during service: While high temperatures can affect the performance of GRP, they are more likely to cause thermal expansion issues rather than direct delamination.
  3. Contamination during manufacturing: Contamination can affect the bond and quality of the laminate but is not typically a primary cause of delamination compared to moisture ingress and poor adhesion.

D. Vibrations from onboard machinery, excessive cleaning with harsh chemicals, and poor design of hull shape.

• Why it's incorrect:
  1. Vibrations from onboard machinery: Vibrations can cause wear and tear but are not a primary cause of delamination. Structural integrity issues are more often linked to moisture and impact damage.
  2. Excessive cleaning with harsh chemicals: While harsh chemicals can damage the surface, they are not a typical cause of delamination. Delamination is more related to internal issues within the laminate.
  3. Poor design of hull shape: Poor design might lead to other problems, but delamination is more directly related to internal bonding issues and moisture ingress.