5.3 Deck Maintenance: Chipping, Wire-Brushing, Painting & Working Aloft/Overside

Introduction to Shipboard Deck Maintenance

A merchant ship operates continuously in one of the world's most aggressive environments. High humidity, constant salt spray, intense solar ultraviolet (UV) radiation, temperature fluctuations, and cyclic wave flexing subject steel hull plates and deck structures to relentless corrosion. Preserving structural integrity through systematic surface descaling, painting, and deck maintenance is a primary daily responsibility of the deck department. General Purpose (GP) Ratings must understand the chemical mechanisms of corrosion, master pneumatic descaling tools, apply marine coating systems safely, and execute high-risk operations—including working aloft on masts and overside on ship stages—under strict statutory safety regulations.

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1. Corrosion Mechanisms on Steel Ships

Mild steel (an alloy of iron with approximately 0.15% to 0.25% carbon) constitutes the primary structural material of merchant ships due to its high tensile strength, ductility, and weldability. However, iron is thermodynamically unstable in its refined state and naturally oxidizes back to iron oxide.

The Electrochemical Process of Rusting

Corrosion on a ship's steel hull is an electrochemical process requiring four elements: an anode, a cathode, an electrical conductor (the steel plate itself), and an electrolyte (seawater or moisture):

1. Anodic Reaction (Oxidation): Iron atoms at the anode lose electrons and dissolve into positive ferrous ions: $\text{Fe} \rightarrow \text{Fe}^{2+} + 2e^{-}$
2. Cathodic Reaction (Reduction): Electrons flow through the steel to cathodic sites where dissolved oxygen in the moisture consumes them, forming hydroxide ions: $\text{O}_2 + 2\text{H}_2\text{O} + 4e^{-} \rightarrow 4\text{OH}^{-}$
3. Rust Formation: Ferrous ions and hydroxide ions combine to precipitate ferrous hydroxide, which oxidizes further with atmospheric oxygen into hydrated ferric oxide (rust): $4\text{Fe} + 3\text{O}_2 + 2\text{H}_2\text{O} \rightarrow 2\text{Fe}_2\text{O}_3 \cdot \text{H}_2\text{O}$

Role of Seawater: Pure fresh water has low electrical conductivity. Seawater contains dissolved salts (primarily sodium chloride, $NaCl$, with an average salinity of 3.5%), forming a conductive electrolyte that supports ionic current and accelerates corrosion. The rate depends on exposure, oxygen, temperature and the condition of the steel and its protective coating.

Galvanic Corrosion & Sacrificial Anodes

When two dissimilar metals are immersed in seawater and connected electrically, a galvanic cell (battery) is established:

• The more active metal (higher on the galvanic series) becomes the anode and corrodes rapidly.
• The more noble metal (lower on the galvanic series) becomes the cathode and is protected.

               GALVANIC CELL AT STERN FRAME
            [Seawater Electrolyte (Conductive)]
             ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
            |                                 |
      [Zinc Anode] --------------------> [Steel Hull] ----> [Bronze Propeller]
      (Very Active)    Electrons Flow     (Protected)          (Most Noble)
      Corrodes Away                       Protected            Protected

• Shipboard Propeller Example: A merchant vessel's propeller is typically cast from nickel-aluminum bronze (NAB), which is far more noble than the mild steel hull plating. Without galvanic protection, the steel stern frame and rudder plating would act as an anode to the bronze propeller, suffering catastrophic localized pitting corrosion.
• Sacrificial Anodes: High-purity zinc or aluminum blocks are bolted or welded to the hull plating adjacent to the propeller, rudder, sea chest strainers, and inside water ballast tanks. Because zinc and aluminum are more chemically active than mild steel, they corrode sacrificially, generating a protective cathodic electron flow to the hull. Sacrificial anodes must be inspected during drydocking and replaced whenever wasted by 50% or more. Never paint over sacrificial anodes! Paint insulates them, destroying their galvanic circuit.
• Impressed Current Cathodic Protection (ICCP): Modern ocean-going vessels augment or replace sacrificial anodes with automated ICCP systems. An onboard DC power supply impresses a controlled protective electrical current into the seawater via non-sacrificial titanium anodes, monitored continuously by hull-mounted zinc reference cells.

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2. Surface Preparation Methods and Cleanliness Standards

No marine paint can protect steel unless the underlying surface is properly prepared. Applying high-performance paint over loose rust, mill scale, moisture, or grease guarantees premature coating blister, delamination, and rapid sub-surface steel wastage.

Descaling Tools and Equipment

1. Hand Descaling Tools:
   • Chipping Hammer: Forged steel head with a chisel point on one side and a conical pick on the other. Used to crack thick rust scales and slag crusts. Caution: Avoid striking clean steel heavily to prevent gouging notches that become stress risers.
   • Scrapers: Flat, stiff hardened steel blades mounted on wooden or fiberglass handles. Used to scrape away loose paint blisters, scale flakes, and grease deposits.
   • Wire Brush: Hand-held stiff steel wire bristles used to sweep away pulverized rust dust and provide a clean mechanical key for paint adhesion.
2. Mechanical Descaling Power Tools:
   • Pneumatic Needle Gun (Needle Scaler): A pneumatic percussion tool driving a bundle of 19 to 28 hardened high-tensile steel needles at 3,000 to 4,000 blows per minute. Ideal for descaling pitted plates, weld seams, angle bars, corners, and rivet heads where flat tools cannot reach.
   • Rotary Descaling Machine ("Rust Bus" / Deck Scaler / Aurand Tool): A wheeled or handheld machine with high-speed rotating drums fitted with hardened steel star cutters or chain flails. Designed for rapid descaling of large flat horizontal deck surfaces.
   • Pneumatic / Electric Angle Grinder: Fitted with braided wire cup brushes, abrasive grinding stones, or flap discs. Used to smooth rough welds and feather the edges of existing sound paint.
3. Abrasive Blasting & Hydro-blasting:
   • Dry Abrasive Blast Cleaning: Compressed air propels sharp abrasive grit (copper slag, garnet, or steel shot) at high velocity against steel, stripping rust down to bare metal and imparting an angular surface anchor profile ($50\text{ to }75\,\mu\text{m}$).
   • Hydro-blasting (Ultra-High Pressure / UHP Water Jetting): Uses fresh water pressurized up to 2,000 to 3,000 bar (30,000 to 44,000 psi). Effectively removes all old coatings, rust, and microscopic salt crystals trapped in steel pores without producing hazardous airborne silica dust clouds.

International Surface Cleanliness Standards (ISO 8501-1 / SIS 055900)

Surface cleanliness before coating application is internationally rated under ISO 8501-1:

Mandatory Personal Protective Equipment (PPE) for Descaling

Surface descaling generates flying metal shards, pulverized iron oxide dust, and intense acoustic vibration:

• Eye & Face Protection: Impact-resistant safety goggles conforming to EN 166 / ANSI Z87.1, supplemented by a full-face clear polycarbonate shield during needle gunning and grinding.
• Hearing Protection: Grade 5 ear muffs or high-attenuation ear plugs. Pneumatic needle scalers generate noise levels exceeding 105 to 110 dB(A), which can cause permanent acoustic trauma within minutes without protection.
• Respiratory Protection: Use correctly fitted respiratory protection selected for the actual dust and exposure. Identify old coating hazards first; avoid sanding or abrasive blasting of known lead paint and use the approved controlled-removal method.
• Riggers Gloves: Suitable gloves protect against cuts and keep hands warm and dry. They do not control vibration exposure; use maintained low-vibration tools and limit exposure time.
• Safety Footwear: Steel toe-cap safety boots with puncture-resistant soles and metatarsal guards.

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3. Marine Paint Systems, Chemistry & Paint Locker Safety

Marine paints are formulated chemical coatings designed to isolate steel from water and atmospheric oxygen, resist mechanical abrasion, and prevent marine biofouling.

The Four Components of Marine Paint

1. Pigment: Finely pulverized inorganic or organic powders. Functions include providing color and opacity, building film thickness, and delivering active chemical corrosion inhibition (e.g., zinc phosphate, red iron oxide, zinc dust).
2. Binder (Resin): The film-forming polymer backbone of the paint. As the paint dries or cures, the binder solidifies into a continuous, tough plastic film adhering to the steel. Common marine binders include epoxy (superior adhesion and chemical barrier), polyurethane (UV and gloss retention), and alkyd (traditional oil-based drying resin).
3. Solvent (Thinner): A volatile liquid that dissolves the resin, reducing viscosity to enable smooth application by brush, roller, or spray gun. Solvents evaporate completely into the atmosphere during drying and do not remain in the cured film.
4. Additives: Specialized chemicals added in small percentages to modify properties: dryers (catalysts), plasticizers, anti-skinning agents, and biocide antifoulants.

The Three-Tier Marine Coating System

A complete marine protective system consists of three distinct layers applied in succession:

               THREE-TIER MARINE COATING SCHEME
     _______________________________________________________
    [  FINISH / TOPCOAT  ] - UV stability, weather resistance, gloss
    [ INTERMEDIATE COAT  ] - Moisture barrier, builds film thickness (DFT)
    [    PRIMER COAT     ] - Anti-corrosive, zinc-rich, adheres to steel
    =======================================================
    [   STEEL SUBSTRATE  ] - Descaled to Sa 2.5 standard

1. Primer Coat: Applied directly to bare, clean, descaled steel before flash rusting occurs. May contain inhibitive pigments such as zinc phosphate, or sacrificial zinc dust, held in a film-forming binder such as a cured epoxy. Protection comes from the barrier, inhibition or sacrificial action provided by the specified formulation.
2. Intermediate Coat (Undercoat): Formulated with micaceous iron oxide (MIO) or high-build epoxy. Builds overall Dry Film Thickness (DFT, typically 100 to 200 $\mu\text{m}$ per coat) and creates an impermeable barrier that blocks moisture and salt ions.
3. Finish Coat (Topcoat): The outermost layer exposed to the weather. Formulated from acrylic polyurethane or modified alkyds to provide high gloss, color stability against UV sunlight fading, and chemical wash resistance.

Antifouling Systems & The IMO AFS Convention

Marine biofouling—the accumulation of barnacles, tubeworms, macro-algae, and slime on underwater hull plating—increases frictional resistance through the water by up to 40%, drastically increasing vessel fuel consumption and greenhouse gas emissions.

• The IMO AFS Convention: In 2001, the International Maritime Organization (IMO) adopted the International Convention on the Control of Harmful Anti-Fouling Systems on Ships (AFS Convention). The convention globally banned organotin compounds, specifically Tributyltin (TBT), because TBT leached into coastal waters, causing endocrine disruption, shell deformation in commercial oysters, and sex change (imposex) in marine snails.
• Modern Antifouling Systems:
  • Controlled Depletion Polymers (CDP) & Self-Polishing Copolymers (SPC): Contain copper compounds (cuprous oxide) paired with organic booster biocides. As seawater flows past the moving hull, the outer microscopic paint layer hydrolyzes and polishes away at a steady rate, continually exposing fresh active biocide.
  • Foul-Release Systems: Completely biocide-free coatings based on fluoropolymer silicone technology. Creates an ultra-smooth, hydrophobic "non-stick" surface. Marine organisms can settle while the ship is stationary in port, while water flow over the moving hull helps detach weakly attached growth. These coatings reduce adhesion; they do not guarantee a completely clean hull at one universal speed.

Safe Application & Paint Locker Regulations

• Application Tools:
  • Brushes: Used for "stripe coating" weld seams, sharp edges, rivets, and bolt heads before general coating, and for small touch-up areas.
  • Rollers: Used for rapid manual application on broad flat bulkheads and deck areas.
  • Airless Spray: High-production system pumping paint at hydraulic pressures up to 200 to 300 bar (3,000 to 4,500 psi). Critical Safety Hazard: The spray gun tip can inject toxic paint directly through human skin into the bloodstream (fluid injection injury). Never place fingers near the spray nozzle or point the gun at anyone!
• Paint Locker Statutory Safety Regulations:
  • Ventilation: Maintain the approved ventilation arrangement and ensure adequate ventilation before entry or paint handling. Solvent vapor can collect low down; keep ventilation openings clear and control ignition sources.
  • Electrical Safety: Use only the certified electrical equipment approved for the locker's hazardous-area classification. Do not introduce ordinary sparking equipment or alter fittings.
  • Fire Protection: Maintain the SOLAS-approved extinguishing arrangement, operable from outside the protected space. Follow its posted instructions; do not enter a burning locker to operate it.
  • Storage: All paint and thinner cans must be kept tightly sealed. Storage of oily rags in paint lockers is strictly prohibited: rags soaked in linseed oil or solvents can ignite spontaneously through exothermic oxidation. Oily rags must be discarded in airtight, heavy-gauge metal drums with self-closing lids.
  • Safety Data Sheets (SDS): Keep the manufacturer's current SDS readily available for the paints, thinners and curing agents, and use them in the task risk assessment.

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Scaffold and Tower Safety

Only trained competent personnel should erect, alter or dismantle scaffolding, following the approved design and instructions. Before use, check its inspection/authorization status, firm support, secure ties or bracing, safe access, complete platforms, guardrails and toe-boards. Do not use an incomplete or damaged scaffold.

Keep the total people, tools and materials within its safe working load. Secure a mobile tower against unintended movement and never move it while people or materials remain on it. Keep the area below clear of falling-object hazards. After alteration, damage or weather that could affect stability, obtain the required competent inspection before using it again.

4. Working Aloft and Working Overside Safety Regulations

Working aloft (on masts, funnel, radar towers, or crane jibs) and working overside (on ship stages or hull ladders) represent two of the highest-risk operations performed by deck ratings. Falls from height or into the sea are frequently fatal. Plan these tasks under the ship's Safety Management System (SMS), risk assessment and permit procedures. COSWP provides practical guidance for controlling their hazards.

Mandatory Permit to Work (PTW)

Before any crew member ascends aloft or suspends overside:

1. Obtain the Working Aloft / Overside Permit required by the ship's SMS, signed by the designated authorized officer after the specified precautions have been checked.
2. A formal Risk Assessment and Toolbox Talk must be conducted on site with all involved ratings.
3. The permit covers only the specified task, conditions and validity period. Follow SMS limits and formally transfer responsibility or renew authorization when required; COSWP's general permit guidance limits validity to 24 hours.
4. Assess ship movement, wind, sea conditions, visibility and lighting before work. Do not proceed when conditions make the task unsafe; follow the approved equipment and ship-specific limits, and stop if conditions deteriorate.

          BOSUN'S CHAIR — SEPARATE SUPPORT AND SAFETY PATHS
       [Suspension strong point]       [Independent safety anchorage]
                 |                                |
          [Gantline block]                    [Safety lifeline]
                 |                                |
             [Gantline]                    [Compatible rope grab]
                 |                                |
        [Double sheet bend]                [Approved connector/
        [Tail seized securely]                energy absorber]
                 |                                |
          [Chair bridle]                   [Full-body harness]
                 |                                |
            [Chair seat] ----- Worker wearing harness
        The safety line does not pass through the chair's block.

The Bosun's Chair: Construction & Rigging

The bosun's chair is a single-person suspension seat used for working aloft:

• Construction: Made from a sound, seasoned hardwood plank (elm or oak, minimum dimensions approximately $450 \times 200 \times 25\text{ mm}$). Four holes are drilled through the corners, through which a 4-strand rope bridle passes, crossing underneath the seat to ensure the plank cannot split or drop away.
• The Gantline: The suspension rope (typically 16 to 18 mm natural manila or certified synthetic line) must be thoroughly inspected for internal rot, strand wear, or chemical damage before each use.
• Securing the Gantline: Reeve the gantline through the approved block. Where using the COSWP rope attachment, secure it to the chair's eye with a double sheet bend, leave an adequate tail and seize the end to the standing part. Have a competent person inspect the entire rig before anyone is hoisted.
• Independent Safety Lifeline (Mandatory):

  Important

  The seafarer MUST wear an approved full-body safety harness connected via a shock-absorbing lanyard to an independent lifeline equipped with an automatic fall-arrest rope grab. The safety harness must NEVER be attached to the bosun's chair, bridle, or gantline! If the gantline parts or the block fails, only the independent lifeline will prevent a fatal fall.

The Stage (Working Overside)

A stage is a heavy wooden plank suspended horizontally along the ship's side plating to allow ratings to chip, clean, and paint the topsides:

• Construction: A sound wooden plank fitted with transverse wooden cleats on its underside. The cleats prevent the plank from splitting and project outward to hold the stage away from the steel hull, providing foot space and handholds.
• Rigging: Suspended by stage ropes secured at each end with a stage hitch locked with two half hitches around the standing part.
• Overside Safety Equipment:
  1. Buoyancy / Lifejacket: Every crew member working overside must wear a certified inherently buoyant work vest or automatic inflatable lifejacket.
  2. Fall Arrest Harness: Connected to an independent lifeline tended from deck.
  3. Deck Standby / Tender: A dedicated rating must be stationed on deck directly above the stage at all times to tend lifelines, monitor the workers, and keep watch.
  4. Lifebuoy on Deck: Keep a lifebuoy with sufficient attached line ready nearby for immediate use. The line must reach the water and the person to be recovered.
  5. Safety Net: Rig a suitable safety net where the risk assessment identifies it as necessary and appropriate; it does not replace the approved harness/lifeline arrangement.

Critical Safety Isolations Before Working Aloft

Before any rating ascends a mast, funnel, or superstructure: