In a GRP boat the hull is built up layer by layer inside the mould, and once cured it cannot be looked into. So laminate supervision happens while the plies go down, not afterwards.
Shop conditions
For the resin to cure properly, shop temperature and humidity must be within the resin maker's limits. Values are logged at the start of each shift and throughout lamination.
Ply-by-ply supervision
- Gelcoat
- Even thickness within the maker's range; thin gelcoat cracks, thick gelcoat is brittle.
- Laminate schedule
- Type, weight and orientation of each ply checked against the schedule; plies counted and recorded.
- Resin ratio
- Too much resin means weight and brittleness; too little means dry, weak areas.
- Voids
- Prevented by rolling in hand lay-up, and by vacuum and resin flow in infusion.
- Core placement
- Full bond to the skin; joints and edges filled.
- Internal structure bond
- Floors and frames bonded to the skin; tabbing width and surface preparation.
Evidence
- Witness panels: small panels made with the same resin and fabric.
- Cut-outs: pieces cut for through-hulls show ply structure and thickness.
- Cure check: hardness testing by the yard or a laboratory.
- Photographs: every ply and every joint.
Continue with this topic
- GRP yacht building: Production method and critical points.
Temperature and humidity record
Laminate quality depends heavily on shop temperature and humidity. The resin maker gives a temperature range and a maximum humidity for application; laminating outside that range may not cure fully or may cause surface problems. So temperature and humidity are measured regularly and written into the lamination record.
Following the ply schedule
The ply schedule states how many plies, which fibre and which orientation go in each area. Ticking off each ply on a checklist prevents a ply being missed or laid in the wrong direction. Where loads are high, such as the keel area, engine beds and deck attachments, the correct ply count is critical.
Thickness and weight
Laminate thickness is checked on cut-outs from through-hull holes or by ultrasonic measurement. Weighing resin and fibre keeps the fibre ratio, and so weight and strength, under control. Too much resin means extra weight; too little means a dry, weak laminate.
Checking cure
Whether the laminate has cured is checked by surface hardness readings and by allowing the maker's time. The hull is not demoulded before the maker's recommended time.
Defects looked for
- Air bubbles and voids between plies.
- Areas of dry fibre.
- Fibre not following the mould in corners and turns.
- Foreign matter or contamination on the surface.
Defects found are marked and put right before the next ply goes on.
Records
The lamination record, with shop conditions, batch numbers and ply checklists, goes into the build file.
Check point
Completing the hull laminate is one of the build's payment-linked check points. The lamination record, thickness readings and photos are reviewed, and the skin looked over once more before internal structure goes in. Once the structure is in, most of the inner surface can no longer be seen, which is why the check is made now.
Any shortfall found is put right before the structure goes in and documented with a photo, so the skin's quality stays on record in the build file, with readings and images, ready to answer any later question.
The record passes to the owner at handover, with the rest of the build file.