Protection for Festival Cruises Mistral
Protection for Festival Cruises Mistral
Keywords: Jotun, Marine corrosion, Cathodic protection, Epoxy coatings
Built at St Nazeire, by Chantlers de l'Atlanique for the Greek operator Festival Cruises, the 1,200-passenger cruise ship Mistral is protected against corrosion and fouling by Jotun Paints systems (Plate 2). For example,the vessel's hull and sea water systems feature Jotun-designed cathodic protection, while her water ballast tanks are protected by the recently introduced "Polyguard SS" solvent-free modified epoxy coating.
Plate 2The Mistral cruise ship, protected by Jotun Paints systems
Jotun Paints is now involved in the design, manufacture and supply of cathodic protection systems. It reports that it can offer a single source for the dual systems of coatings and cathodic protection necessary for optimum protection of a vessel's hull.
As readers will know there are two appropriate cathodic protection systems,namely the widely-used sacrifical-anode system (SACP) and the impressed-current system (ICCP) which was chosen for the Mistral. The ICCP system anodes fixed to the hull are connected to the positive pole of a DC supply, the negative pole being connected to the hull. The anodes are made of very inert materials, platinum for example, to give a working life of up to 15 years.
ICCP claims a number of technical and economic advantages over SACP. These include good control over hull condition, an ability to neutralise the corrosive effects of paint damage and easy retrofit, even under water. The ICCP anode being recessed, the hull outer surface remains smooth with minimum drag.
"Seamate HB 66", from Jotun's range of high-performance self polishing antifoulings, was chosen for the underwater hull of the Mistral. Specifically designed for cruise ships and other low-activity vessels, this product claims from three to five-years' fouling protection anywhere in the world.
Above the waterline, topside, superstructure and decks are protected by the aluminium version of Jotun's "Jotsmastic 87" modified epoxy mastic coating. With a claimed high surface tolerance, "Jotamastic 87 Aluminium" adheres well, and can be applied in high film thicknesses. It contains little solvent and is stated to be not isocyanate.
Sea water systems
Fouling in sea water systems can lead to turbulence, impaired heat transfer and blocked pipelines, giving rise to potentially dangerous situations,particularly with the fire fighting system. Cleaning and the application of antifouling can be difficult and costly, so protection is frequently provided by chlorination, chemical dosing or an electrolytic system.
Because of the corrosive action of chlorine on steel, and the pollution resulting from the discharge of dosing chemicals into the sea, Jotun decided to focus on an electrolytic system.
In the fully automatic "Cuproban" system, incoming water is treated electrolytically at its point of entry, in a small ICCP cathodic-protection system using a combination of copper anodes and aluminium/soft-iron anodes. A closely controlled quantity of "floc" is formed and carried through the sea water system to combat fouling and, to a certain degree, corrosion. The amount of copper and aluminium/soft-iron released from the anodes is believed to be very small, and Norwegian health authorities allow the use of "Cuproban" treated water for drinking purposes.
"Cuproban" is said to be simple to install in new or existing sea water systems and, being self-monitoring, requires minimal supervision and maintenance.
Ballast tanks
The water ballast tanks of the Mistral are protected by Jotun's recently introduced "Polyguard SS" ballast tank coating. Reported to be solvent-free, this is believed to be suitable for both new buildings and maintenance and is said to be surface tolerant with good wetting properties and excellent adhesion. "Polyguard SS" is produced in light colours (grey, green,beige and red) to ease application and inspection in the ballast tanks.
Along with Jotun's other ballast tank coatings ("Balloxy HB Light" and"Balloxy NB Light"), "Polyguard SS" has been tested and classified by Marintek. Intended for newbuilding projects, the coating is designed for use on fully prepared surfaces, but can be applied to minor areas that have been manually prepared. "Polyguard SS" is stated to be compatible with cathodic protection.
"Naviguard"
The fresh water tanks of the Mistral have been coated with solvent-free epoxy, while engine room and accommodation are protected by an alkyd primer and "Marine Gloss White" topcoat.
Further details are available from Jotun Paints. Tel: +47 33 457000; Fax: +47 33 464613.
