Part (a): Causes of delamination
The question asks for three possible causes of delamination in GRP hulls. Here are three potential answers:
- Stress on the hull: Physical stress on the hull can cause the layers of fiberglass and resin to separate. This can happen due to impact, grounding, or overloading.
- Water ingress: If water gets into the laminate, it can weaken the bond between the layers and lead to delamination. This can happen through cracks in the gelcoat, poor sealing around fittings, or inadequate drainage.
- Poor construction: Defects in the construction of the hull, such as voids in the laminate or improper curing of the resin, can also lead to delamination.
Part (b): Detecting delamination
The question asks for two methods of detecting delamination in service. Here are two options:
- Tapping: Gently tapping on the hull with a mallet or other blunt object can produce a hollow sound if there is delamination beneath the surface.
- Visual inspection: Looking for signs of cracking, bulging, or discoloration in the gelcoat can also indicate delamination.
Part (c): Repairing delamination on a sandwich construction hull
The question asks for two methods of repairing delamination on a sandwich construction hull. Here are two possibilities:
- Vacuum injection: This technique involves injecting resin under pressure into the delaminated area to fill the voids and rebond the layers.
- Grouting and re-laminating: This method involves removing the damaged material, filling the delaminated area with epoxy grout, and then re-laminating the surface.
Part (d): Design problems leading to stress cracking
The question asks for three design problems that can lead to stress cracking in GRP hulls. Here are three potential answers:
- Sharp corners: Sharp corners in the hull design can create stress concentrations that make the material more susceptible to cracking.
- Inadequate stiffening: If the hull is not properly stiffened, it can flex under load and develop cracks over time.
- Discontinuities in the laminate: Holes, cutouts, or other discontinuities in the laminate can also create weak points where cracks are more likely to occur.
These are just some possible answers to the questions in the image. The specific causes, detection methods, and repair techniques for GRP hull defects will vary depending on the individual case.