Superstructure icing
Superstructure icing is a significant threat to boats and cutters operating in cold northern waters. [2] [3] Longer sea ice-free periods attributable to global change will be accompanied by longer fetches. Frequent and long duration high winds, combined with extended fetch, produces greater wave heights and will make superstructure icing more severe than it is today. [2] [3] [4]
Sea spray can produce ice on both decks and superstructures.
Typical icing problems encountered are:
- impairment of stability owing to the raised center of gravity, which increases the rolling moment of the ship
- decreased freeboard
- impaired communication, navigation, and radar capabilities caused by antenna icing
- accumulated ice preventing the functioning of certain deck equipment, such as winches
- may hinder access to rescue equipment, such as lifeboats and life rafts
- safety of operations on decks and equipment
- air intakes may become clogged with ice
- ice on wheelhouse windows, gangways, decks, and railings covered by ice make it difficult and dangerous to operate safely
- scuppers and drains are often reduced in area and may even completely clog, impairing deck drainage increasing ice accumulation
Superstructure icing usually refers to one type of icing—that which occurs when sea spray is lofted over the ship and freezes on the superstructure. At sea this is saline water creating saline ice; on lakes and rivers, it is fresh water creating fresh water ice. Atmospheric ice also forms on ship superstructures: ice that originates from atmospheric sources. Atmospheric ice includes frost, rime, snow, sleet, and glaze. Each ice type creates its own hazards and potentially reduces safety. [5]
Active plunging of ship bows into waves and swells, through displacement, hydrodynamically lofts columns of water that are entrained into the relative wind. That spray is then carried over the superstructure by the relative wind and causes ship icing to be more severe than icing of stationary structures such as offshore platforms. [7] [8]
Knowledge of the presence of superstructure ice, and its thickness and distribution, is critical to the safety of boats and cutters. Though ice accumulation sufficient to threaten ship stability can be visually recognized easily during daylight, small thicknesses of ice sufficient to make decks slippery are less easily seen by eye. In addition, icing at night may not be detected until a significant amount has accumulated. Ice detection technologies have made considerable advances in the last 20 years [9], but the operating environment of a seagoing boat or ship is hostile.
More on this topic: icing on ships
References
- ↑ CGC BISCAYNE BAY photos courtesy LCDR Godwin, USCG; CGC THUNDER BAY photos by CRREL 2012
- ↑ 2.0 2.1 Wise, J., and A. Comiskey. 1980. Superstructure Icing in Alaskan Waters. NOAA Special Report. Boulder, CO: US Department of Commerce, National Oceanic and Atmospheric Administration, Environmental Research Laboratories.
- ↑ 3.0 3.1 Brown, R., and P. J. Roebber. 1985. The Ice Accretion Problem in Canadian Waters Related to Offshore Energy and Transportation. Canadian Climate Center Report 85-13. Ontario: Atmospheric Environment Service, Climatological Services Division.
- ↑ Wang, M., J. E. Overland, and P. Stabeno. 2012. Future climate of the Bering and Chukchi seas projected by global climate models. Deep Sea Research II 65–70: 46–57.
- ↑ 5.0 5.1 Charles C. Ryerson. April 2013. Icing Management for Coast Guard Assets. Cold Regions Research and Engineering Laboratory. ERDC/ C R R E L TR-13-7.
- ↑ CGC BISCAYNE BAY photos courtesy LCDR Godwin, USCG; CGC THUNDER BAY photos by CRREL 2012
- ↑ Itagaki, K. 1984. Icing rate on stationary structures under marine conditions. CRREL Report 84-12. Hanover, NH: US Army Cold Regions Research and Engineering Laboratory
- ↑ Minsk, L. D. 1984b. Assessment of ice accretion on offshore structures. Special Report 84-4. Hanover, NH: US Army Cold Regions Research and Engineering Laboratory.
- ↑ Ryerson, C., and A. Ramsay. 2007. Quantitative ice accretion information from the automated surface observing system (ASOS). Journal of Applied Meteorology and Climatology 46:1423–1437.