- With reference to the application of protective coatings to a vessel’s hull:
(a) state the functions that the coating should perform;(3)
(b) state the legislation that applies to certain coatings and what certification is required to comply with it;(2)
(c) outline the process for re-coating the hull of a vessel in drydock.(5)
(a) Functions of the Coating (3 marks)
Protective coatings applied to a vessel’s hull must perform the following functions:
- Corrosion protection – prevent seawater, oxygen, and electrolytes from attacking the steel hull.
- Fouling prevention – discourage the attachment of marine growth such as barnacles and algae, which increase drag and reduce efficiency.
- Surface protection and improved efficiency – provide a smooth surface that reduces frictional resistance, improving fuel economy and maintaining vessel speed.
(1 mark per correct function = 3 marks)
(b) Legislation and Certification (2 marks)
- The use of antifouling systems is governed by the International Convention on the Control of Harmful Anti-Fouling Systems on Ships (AFS Convention), adopted by the International Maritime Organization (IMO).
- This legislation prohibits the use of harmful organotin compounds, such as tributyltin (TBT), on all vessels.
- Compliance requires that vessels carry an International Anti-Fouling System Certificate (IAFS Certificate) issued by the flag administration or recognised organisation after inspection and approval of the coating system.
(1 mark for legislation + 1 mark for certificate = 2 marks)
(c) Process for Re-Coating the Hull in Drydock (5 marks)
- Preparation and safety precautions
- Vessel is securely docked; scaffolding and staging are erected.
- Environmental and safety checks carried out (ventilation, PPE, containment of debris).
- Surface cleaning
- All marine growth and old coating are removed by high-pressure washing or abrasive blasting (typically to Sa 2½ standard).
- Surfaces are inspected for corrosion, damage, or pitting.
- Surface inspection and repair
- Any steel wastage is repaired; defective welds ground and faired smooth.
- Surfaces must be completely dry and free of grease, oil, or dust before coating.
- Application of coatings
- Apply primer coat immediately after cleaning to prevent flash rusting.
- Follow with intermediate coats (e.g., epoxy anticorrosive) and finally antifouling topcoat, each applied to the manufacturer’s recommended film thickness and curing time.
- Inspection and documentation
- Each layer is inspected for uniform coverage, adhesion, and thickness using appropriate gauges.
- A coating report is completed, and the IAFS certificate updated if antifouling is renewed.
(1 mark per correct step = 5 marks)