(i) The Hull Roughness Analyzer (HRA) is a portable system designed to measure the roughness of a ship’s hull surface. It includes:

• A portable microprocessor with a digital display and printout capability.
• A handheld carriage equipped with a stylus measuring head. The stylus traces the hull surface, recording peaks and valleys to assess roughness.
• The system measures 10 sample lengths of 50 mm during a single traverse over the hull. For each 50 mm sample, the highest peak to lowest valley is recorded as Rt(50).
• Roughness surveys are conducted at approximately 100 locations on the hull, including the bow, stern, midship, and topping. Multiple traverses at each location provide numerous readings.
• Mean Hull Roughness (MHR) is calculated as:
• $$MHR\:=\:\frac{\sum Rt\left(50\right)}{n},\:where\:n\:is\:the\:number\:of\:readings\:at\:a\:station$$
• Average Hull Roughness (AHR) is calculated as:
• $$AHR\:\frac{\sum MHR}{m},\:where\:m\:is\:the\:total\:number\:of\:survey\:stations$$

(ii) Significance of Roughness Profile:

The roughness profile of the prepared hull surface impacts the performance of the applied coating and the overall operational efficiency of the vessel. A rough surface increases frictional resistance as the vessel moves through the water. This increased drag translates to higher power requirements for propulsion, leading to increased fuel consumption and operational costs. Furthermore, greater surface roughness contributes to increased carbon emissions, a concern under current MARPOL regulations. Therefore, a controlled and optimised roughness profile is essential for minimising frictional resistance, reducing fuel consumption and emissions, and maximising the longevity of the hull coating.

Typical Average Hull Roughness (AHR):

• New Ship: 120-200 µm (approx.).
• Eight-Year-Old Ship: 300-400 µm (approx.) due to annual deterioration of 20-40 µm.

Washing:

• The hull surface must be thoroughly cleaned to remove all marine growth (algae, slime, etc.), accumulated salts, dirt, grease, and oil. High-pressure freshwater washing is the standard method for this initial cleaning. The goal is to present a clean substrate for subsequent stages.

Blasting:

• Abrasive blasting is the preferred method for removing rust, defective paint, and any remaining contaminants. This process achieves a bare metal surface, essential for proper adhesion of the new coating. The extent of blasting (localized or full hull) depends on the condition of the existing surface. The intensity and type of abrasive used are carefully controlled to achieve the desired surface roughness profile.

Primer Application:

• After blasting, the surface is again cleaned to remove any blasting debris. A primer coat is then applied to provide corrosion protection and to create an ideal surface for the subsequent topcoat adhesion. This primer acts as an intermediary layer, enhancing the bond between the substrate and the long-life coating system.

(ii) Defects in Self-Polishing Paint Application:

• Blistering: Bubbles caused by trapped moisture.
• Curtaining/Sagging: Paint sagging due to its own weight.
• Dry Spray: Paint particles drying before reaching the surface.
• Peeling/Flaking: Caused by moisture, dust, excessive film thickness, or incompatible paints.
• Cissing/Crawling: Paint contracting immediately after application.