Fig 10 shows a racing kayak designed for competitive sprint events on flat water. (a) (i) Describe the hand layup process used to manufacture the kayak hull...

(a)(i) The hand layup process for manufacturing the kayak hull from CFRP composite: [4]

1. A release agent is applied to the female mould surface to prevent the cured laminate from bonding to the mould. [1]
2. Layers of carbon fibre mat or woven cloth are cut to shape and carefully placed into the mould, following the contours of the hull profile. [1]
3. Epoxy resin is applied to each layer using a brush or roller, thoroughly wetting out the fibres to ensure complete saturation. The roller also removes trapped air bubbles. [1]
4. Successive layers are built up to the required wall thickness. The completed layup is left to cure (harden) either at room temperature over several hours or in a heated oven to accelerate the chemical cross-linking of the epoxy. [1]

(a)(ii) Two reasons why a female mould is used rather than a male mould for the outer hull surface: [2]

1. A female mould produces a smooth outer surface on the hull because the outer face of the laminate forms directly against the polished mould surface. A smooth hull reduces hydrodynamic drag in the water, which is critical for competitive racing speed. [1]
2. The external dimensions are controlled accurately by the mould cavity, ensuring a consistent, precise hull shape from one kayak to the next, which is essential for meeting racing class regulations and maintaining predictable handling. [1]

(b)(i) The composite structure of CFRP is suitable for a racing kayak because: [3]

1. CFRP has an excellent strength-to-weight ratio, meaning the hull can be made extremely strong while adding very little mass. [1]
2. The hull is stiff enough to resist flexing during the high paddling forces of sprint racing, maintaining its designed hydrodynamic shape and transferring the athlete's power efficiently. [1]
3. The composite can be moulded into complex curved shapes, allowing designers to optimise the hull cross-section, bow entry angle, and stern rocker for minimum drag. [1]

(b)(ii) Two properties of CFRP that make it superior to a steel frame: [2]

1. CFRP is much lighter (lower density) than steel, significantly reducing the overall mass the athlete must propel through the water. Every gram matters in competitive sprint events. [1]
2. CFRP does not corrode in fresh or salt water, unlike a steel frame which would need protective coatings that add weight and require maintenance. [1]

(c)(i) Two surface preparation steps before applying epoxy adhesive: [2]

1. Both bonding surfaces must be cleaned and degreased to remove oils, dust, fingerprints, or residual mould release agent that would prevent the adhesive from wetting the surface and forming a strong bond. [1]
2. Both surfaces should be lightly abraded (sanded) with fine abrasive paper to roughen the surface, creating a mechanical key that increases the contact area and allows the adhesive to grip. [1]

(c)(ii) Adhesive bonding is more appropriate than mechanical fixings inside a thin composite shell because: [3]

1. Mechanical fixings such as screws or bolts would require drilling holes through the thin laminate, creating stress concentrations that weaken the shell and could initiate cracking or delamination under the dynamic loads of paddling. [1]
2. Adhesive bonding distributes the load over a larger area of the joint, avoiding the localised stress peaks that occur around bolt holes, resulting in a more durable connection. [1]
3. Drilling through the composite laminate could also allow water ingress between the carbon fibre layers, leading to delamination, fibre damage, and progressive structural degradation. [1]

(d)(i) Two quality control checks on the finished composite hull: [4]

1. Visual inspection of the outer surface for cracks, dry patches (areas of unsaturated fibre), surface blemishes, or resin-rich/resin-starved zones. Surface defects indicate manufacturing faults that may compromise structural integrity. [1]
2. Tap testing: the hull is tapped systematically with a coin or small hammer. A consistent, sharp sound indicates solid laminate; a dull or hollow sound at any point indicates delamination or a void, where layers have separated internally. [1]
3. Additional checks include: measuring the hull wall thickness at key points using an ultrasonic thickness gauge to ensure uniformity across the laminate [1]; and checking overall dimensions and symmetry against the design drawing to confirm the hull meets the specified tolerances and class regulations [1].

(d)(ii) If air pockets become trapped between layers of carbon fibre during layup: [2]

1. The air pockets (voids) create weak spots in the laminate where the fibre and resin are not bonded together, reducing the local strength and stiffness of the hull wall. [1]
2. Under the repeated loading of paddling, these voids can initiate delamination or cracking, causing layers to separate and the hull to fail progressively, potentially leading to catastrophic structural failure during a race. [1]

(e) Three advantages of vacuum bagging over hand layup for producing composite structures: [3]

1. Vacuum bagging compresses the laminate more evenly across the entire surface, significantly reducing voids and trapped air pockets compared to manual roller consolidation. [1]
2. The compression produces a higher fibre-to-resin ratio, because excess resin is squeezed out. This results in a stronger, stiffer, and lighter finished part because carbon fibre (not resin) carries the structural loads. [1]
3. Vacuum bagging gives a more consistent laminate thickness across the entire hull, reducing variations in wall thickness that can cause uneven performance and localised weakness. [1]