Regardless of the type of vessel you operate—motor boats, sailing yachts, monohulls or multihulls—it is essential that the hull remains in optimal condition. Even with regular maintenance, chips, cracks and scratches are inevitable over time.
Hull repairs may be carried out by specialised professionals or as part of scheduled maintenance (for charter vessels). However, if you intend to undertake repairs yourself, the following expert recommendations will guide you effectively.
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Repairing minor cracks or chips
For small cracks or surface chips, the use of a repair gelcoat is recommended. Gelcoat is available either pre-mixed or requiring preparation, and can be applied using a brush or spatula.
A finishing gelcoat containing paraffin should then be applied to enable proper curing of the initial layer. Smooth the surface using arelease film (e.g. Terphane), which must be removed prior to sanding.
Gelcoat is available in standard colours, but can also be custom-tinted to match the hull.
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Selecting the appropriate repair products
The choice of resin depends on the location of the repair:
- Above the waterline: use a polyester resin mixed with an accelerator and catalyst
- Below the waterline: use an epoxy resin combined with a hardener (note the rapid curing time)
Fibreglass reinforcement is typically used alongside resin to enhance structural rigidity:
- Woven fibreglass: suitable for flat surfaces
- Chopped strand mat: ideal for building thickness and finishing curved areas
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Addressing cracking, splitting and surface degradation
Over time, hull surfaces may develop micro-cracking and become porous. In such cases, polishing is no longer sufficient, and repainting becomes necessary.
Surface preparation is critical and can account for more than 80% of the final result.
For gelcoat hulls, the standard procedure includes
- Cleaning
- Degreasing
- Fine sanding (320-grit abrasive)
- Removing dust residues with a clean cloth
Preparation methods vary depending on the hull material:
Steel or aluminium hulls:
- In good condition: follow the standard procedure
- In poor condition: strip back to bare metal (acid pickling, grinding or sandblasting)
- Aluminium hulls: sandblasting is strongly recommended
- Wooden hulls: remove old paint by scraping or heat treatment, then apply an anti-fungal and anti-rot protective coating
Finally, mask off all non-painted areas and deck fittings (deck hardware).
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Repainting the hull with marine coatings
Marine coatings are available in two main categories, suitable for most hull types:
Single-pack coatings (acrylic or alkyd-based):
- Moderate resistance
- Good adhesion
Two-pack coatings (polyurethane with hardener):
- Superior finish quality
- Excellent resistance to weathering and marine conditions
Note: wooden hulls (carvel or clinker-built) should be coated with single-pack systems.
Application conditions are critical:
- No wind (to prevent dust contamination)
- Low humidity
- Moderate ambient temperature
- Application in a controlled environment whenever possible
Use appropriate tools: wide brushes, fine foam rollers, finishing pads (for levelling), or a spray gun if you are experienced in its use.
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Antifouling: essential protection below the waterline
Antifouling is a specialised coating containing biocidal agents (EU Regulation No. 528/2012), designed to prevent the accumulation of algae and marine organisms.
For submerged sections of the hull, two main types are available:
- Self-polishing (erodible) antifouling: recommended for faster vessels
- Hard matrix antifouling: high durability, based on insoluble resins
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Lamination: choosing between mat and roving
The choice of reinforcement depends on the repair area:
- Chopped strand mat: randomly oriented short fibres bonded together
- Woven roving (glass fabric): structured fibres forming a fabric, typically used in combination with mat
- Composite reinforcements: combining mat on one side and roving on the other
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Drilling the hull during repairs
When working with composite materials:
- Small-diameter holes: drill using a metal bit, then countersink before inserting screws
- Large-diameter holes: use a hole saw
- Large openings: use a jigsaw after drilling pilot holes for blade insertion
- Sealing: apply a marine-grade sealant such as a Sika marine product
Always wear appropriate personal protective equipment: mask, safety goggles and gloves.
Important note: if yellow dust (Kevlar/aramid fibres) appears during drilling, continue drilling in reverse to prevent the bit from binding.
Hull maintenance and repair require both technical rigour and the correct selection of materials. Whether addressing minor cosmetic damage or undertaking more substantial structural work, adherence to best practices ensures durability, safety and long-term performance.
For complex repairs or high-value vessels, consultation with qualified marine professionals remains strongly recommended.
