DNV Winterized notation: Basic, Cold and Arctic explained

What the notation is

Winterized is an additional class notation in the DNV rules for ships. It is assigned with a qualifier and a design temperature, for example Winterized Cold (−25 °C). The qualifier decides how much of the vessel must be protected and to what level; the design temperature decides the material requirements and the ambient temperature the equipment must function at.

• Winterized Basic: the entry level. Anti-icing or de-icing of the areas and equipment that are essential to safety, so the ship can operate through occasional icing.
• Winterized Cold (t): for regular operation in cold climate. Extends the scope of protected areas and adds requirements for materials, machinery and systems at the stated design temperature.
• Winterized Arctic (t): for continuous operation in arctic conditions, with the most extensive requirements for anti-icing, de-icing capacity, materials and redundancy.

The exact scope for each qualifier is set out in the current edition of the DNV rules for classification of ships, Part 6 (additional class notations). The rules are revised regularly, so the edition that applies to a newbuilding is the one in force at contract date.

Which areas have to be kept free of ice

Across the qualifiers the rules point at the same places: where people move, where they escape and where the ship is operated from. Typical items on the list are:

• Escape routes, walkways, stairs, ladders and handrails, including the routes to the lifeboat and liferaft stations
• Lifesaving appliances and their launching arrangements: lifeboat and MOB davits, release gear and embarkation areas
• Navigation and communication equipment, bridge windows and the clear view forward
• Ventilation intakes and outlets, watertight doors and hatches that must be operable
• Deck machinery that is essential to safe operation, such as anchoring, mooring and towing equipment
• Piping systems that can freeze: fire mains, ballast, drain and cooling water lines above the waterline

Anti-icing means keeping a surface above freezing so ice does not form. De-icing means having the capacity to remove ice that has formed within a given time. Escape routes and lifesaving stations are normally anti-iced; larger deck areas may be handled by de-icing capacity, manual or electrical.

What it means for the electrical heat tracing

Electrical heat tracing is the normal way to meet the anti-icing requirements on walkways, stairs, davits and piping. The design has to show, per circuit, that the heat output keeps the surface above freezing at the design temperature and the design wind speed, and the installation has to be documented for class: cable type and output, junction boxes, thermostats or controllers, alarms, and the certificates.

• Raychem self-regulating heating cables for walkways, piping and equipment, selected by W/m from the heat loss calculation
• TEF 1058 heat trace junction boxes, end seal terminations and marshalling boxes in stainless steel AISI 316L, Ex certified where the circuit runs through hazardous areas
• Capillary or electronic PT100 thermostats, or ThermoConnect TTC controllers with alarms to the bridge when the notation asks for monitoring

What it means for the lighting

Navigation lights, searchlights and floodlights must function at the design temperature. Tranberg navigation lights are proven in arctic waters, the Compact navigation lights have a heating base against ice and snow, and the TEF 2580 and 2581 floodlights are rated to −40 °C.

How to specify it

• State the qualifier and the design temperature from the class documents
• Mark the areas to be anti-iced or de-iced on the GA drawing
• Give the minimum ambient temperature and design wind speed used in the heat loss calculation
• Say whether the circuits run through zone 1 or 2 so the Ex certification is included

The rule references above describe the structure of the notation. The binding requirements are in the DNV rules edition that applies to the vessel; we check the scope against it when we design the system.