Ice poses a serious danger to shipping as impact with it can cause physical damage to the ships structure. In this report I aim to give an overview of Ice and its formation, areas it forms, how to navigate within areas of Ice and the precautions to be taken.
There are two forms of Ice that a seafarer may encounter and they are Sea Ice and Icebergs. Sea Ice is formed in waters in the Frigid Zones in both the northern and southern hemispheres. The Frigid Zone in the northern hemisphere is located north of the Arctic Circle and covers around 4% of the Earth’s surface. The Frigid Zone in the Southern Hemisphere is located south of the Antarctic Circle and again covers around 4% of the Earth’s surface. Sea Ice also forms in areas of the southern Temperate Zone (located between the Tropic of Capricorn and the Antarctic Circle) in the winter season around the Antarctic. In spring time sea ice breaks up and spreads further into the northern and southern temperate zones (the northern Temperate Zone being located between the Arctic Circle and the Tropic of Cancer) in the Antarctic and western north Atlantic.
Sea Ice is formed when the sea water’s surface freezes. This process begins when the surface water cools, therefore increasing its density and it sinks. This water that is sinking is then replaced by warmer water which has a lower density from below the surface water; this is known as convectional descent. This process continues until the sea water has reached its maximum density and convectional descent stops. When this stage is reached ice can now begin to form. Sea Ice forms best in waters where the ‘water column’ is in layers of different density. In this situation the ‘convectional sinking’ occurs in only the uppermost layer of the sea water meaning this process will take less time allowing ice to form earlier.
The maximum density of fresh water is at 4 degrees Celsius which is 39 degrees Fahrenheit. Seawater with a salinity (salt water content) of 25% has a maximum density at a temperature of around minus 1.5 degrees Celsius. From this information it is clear that the formation of sea ice is a long process and especially long if in deep waters with a high salinity due to ‘convectional descent’ taking a long time. Some areas do not have long enough winters for sea ice to form but where sea ice is most likely to form first is in shallow waters where the process of convectional sinking takes the least amount of time, allowing sea ice to form.
When sea ice begins to develop there will firstly be needle shaped ice crystals known as Frazil Ice and they give the sea an oily appearance. The ice crystals within Frazil Ice then thicken and group together to form Grease Ice which gives the surface of the sea a greasy and soupy layer. If snow falls Slush will be formed at this stage. Spongy lumps of ice a few centimeters across in size will then start to form that are known as Shuga Ice. The Ice classes mentioned above namely Frazil Ice, Grease Ice, Slush and Shuga Ice are all classed as New Ice.
The process then continues until Pancake Ice forms which are flat, circular pieces of ice which will eventually group together to form a continuous ice sheet called Young Ice. The young ice may however become broken up due to wave action. Young Ice may however thicken and become what is known as Field or Pack Ice. These are terms used to describe fully developed sea ice floating on the ocean that is not attached to the shore in any way. Field and Pack Ice can vary from being just a few inches deep to several feet deep and can be very dangerous to sea farers. Pieces of such ice more than 20 meters across are known as Floes and the pack of ice can be called either; open, very open, close or very close, depending on how close the Floes are to each other. A very close pack of ice may leave no water visible at all and pack ice originating from the Arctic or Antarctic is usually several feet thick and very uneven. It is uneven due to a process known as Hummocking, which is where the waves cause ice to pile up.
Icebergs are formed not at sea like Sea Ice, but are pieces of ice that have broken off from the seaward side of Glaciers. This happens because as a Glacier expands, the force of buoyancy of the water leads to ice being broken off the Glacier and icebergs are then calved. Icebergs are therefore irregular in shape and sometimes contain debris of rock and soil from the land the Glacier formed on which is why they are so dangerous to seafarers. Ice bergs that originate from the Antarctic sometimes break off Glaciers but mainly break off the outer limits of the ice shelf that skirts the edge of the continent. It is thought that they break off due to seismic activity. They are flat topped with steep sides and several miles in size. Due to their shape they are named ‘Tabular Bergs’.
Ice bergs only have around an eighth of their total volume above the waterline which is why they pose such a danger to ships. The name Growler is used to describe an iceberg that is only around 1 meter in size above the waterline. ‘Bergy bits’ is the term used to describe ice bergs that are around 4-5 meters in size above the waterline and the term iceberg is used to describe the largest pieces of ice encountered at sea.
Where ice may be encountered
– Grand Banks of Newfoundland
Between February and May pack ice may be encountered and between April and August, icebergs may be encountered. Icebergs in this area are calved from glaciers on the coast of Greenland during the summer. The icebergs from the east coast are taken down the coast by the east Greenland current to eventually go around Cape farewell. They are then transported up the west coast of Greenland by the west Greenland current. Here they spend the winter trapped in the pack ice that is present on the west coast of Greenland. During the spring these icebergs are then transported to the Grand Banks area by the Labrador Current.
In this region, ice is particularly dangerous to shipping because of the presence of fog in the spring and summer seasons. However, once the ice goes south of the Grand Banks, it melts quickly in the warmer waters.
– Gulf of St Laurence and River
This area is navigable from the end of April until the end of November. Ice breaker help is sometimes required in this area as large amounts of pack ice may form. Entry into this area is only available via the Cabot Strait until the middle of June when the Belle Isle Strait also allows access.
– Hudson Bay
Navigable from the middle of June until the middle of October with the help of an Ice Breaker if required. In this area toward the beginning and end of the season in which the ice forms is when the most ice is likely to be encountered.
– Eastern Seaboard of North America
Throughout the winter, ice can be present as far south as the Chesapeake Bay.
– Denmark Strait
Pack ice that may be found here extends from the coast of Greenland to the Icelandic coast in the winter and early spring
– White Sea
Navigable from July to September. The northern coast of Norway is almost always ice free due to the North Atlantic Current.
– Baltic Sea
Most ice in this area is found in northern and eastern portion from November to May. Other areas affected from midwinter to early spring are the coast and ports of the Baltic Sea.
– Black Sea
Field ice is found here in the mid winter but mostly only the coast is affected
– North Pacific Ocean
Field Ice may form in the waters of the Japan Sea and the northern part of the Yellow Sea throughout the winter months.
– Southern Ocean
The coast of Antarctica is surrounded by pack ice and icebergs throughout the year. The mean limit of pack ice is 55 degrees south in the mid winter but in mid summer this limit increases to 65 degrees south.
Icebergs may be encountered between latitudes of 35 and 50 degrees south to 50 degrees west. In the western Indian Ocean icebergs may be encountered up to a latitude of 43 degrees south between the months of February and March.
Sources of information on Ice
The Mariners handbook, Chapter 7 ‘Ice’, contains a comprehensive guide to Ice for the OOW. The Mariners handbook also contains an ‘Ice Glossary’ which provides definitions of all terms used when describing ice. This glossary is very important in understanding the terms used in ice bulletins.
Other sources for information on ice, referenced from ‘Navigation Advanced for Mates and Masters’ by Capt. Nadeem Anwar are:
- Ocean Passages for the World
- ALRS (Admiralty List of radio Signals)
- Admiralty Sailing Directions for the local area
- Ice Charts
- Routing Charts
- Weather Facsimile Charts
- Ocean routing services (such as WRI used onboard Aurora)
- Weather and Ice Reports
- NAVTEX and SafetyNET EGC (Enhanced Group Calling) ice reports
- The International ice patrol
- US Coastguard, US Navy Ocean Office, Canadian ice reconnaissance Aircraft Facsimile Service, Baltic Ice Service
- Port Authorities, local Pilots and Pilotage Authorities
- Ocean Weather ships
- Ships departing from the area
- Previous experience and knowledge of individuals onboard
- Previous records onboard if the vessel had been to the island before
Warnings of ice in the vicinity
– Sea ice warning signs
Sea ice may be present if the OOW spots a whitish or yellowish haze during clear daylight. If it is overcast then a whitish glare is an indication of sea ice. White patches in fog are another indication of sea ice. If the swell starts to lessen or if there is a distinct and quick smoothing of the sea then this indicates the presence of ice to windward. Sometimes there may also be a thick band of fog over the edge of the piece of ice.
The presence of marine life is another indication of the presence of ice. For example If in the Arctic the presence of walruses, seals and birds indicate there is ice nearby.
– Iceberg warning signs
If the vessel is far from land and there appears to be no affect on the sea state by the wind then this is an indication that there is an iceberg to windward. If growlers and smaller pieces of ice are spotted this is also an indication of an iceberg located to windward. If the sound of what sounds like the sea breaking is heard when far from land, or thunderous sounds are heard then these are both indications that icebergs are present in the area. These are the sounds that are produced as the icebergs are calved.
In the daytime an iceberg can appear as a luminous white mass in fog. During the night on a clear night when there is no moon, icebergs are visible at a distance of around 1 to 2 miles as white or black objects. Icebergs are clear to see at night if the moon is behind the observer but with intermittent moonlight on a cloudy night icebergs are hard to see. Cumulus and Cumulonimbus clouds can cause the impression of icebergs at night. The OOW must not use changes in the air or sea temperature and echoes from a whistle or any other sound signalling device as a means of identifying if icebergs are present. This is because these methods are not at all accurate at determining the presence of icebergs.
Spotting open water in areas of ice
Dark streaks on the underside of clouds indicator open water and dark streaks on the underside of cloud at high altitude indicate the presence of smaller patches of open water. If it is foggy then the OOW should look out for dark spots in the fog as this indicates that there is open water there at a relatively short distance from the vessel. A noticeable increase in swell indicates that open water is close by.
Navigating in ice
Entering an area where ice is present should ideally be avoided but if entering such an area is unavoidable then the type of ice to be encountered, the time of year (so as to know what point in the ice season it is for the local area), weather conditions and the area to be entered must be fully researched and the OOW must make himself/herself fully aware of all this information. The ship must have an ice classification to navigate in areas of ice and the assistance of an icebreaker should be requested if required. On entering the area of ice it should preferably be during daylight hours. If entering at night or in restricted visibility bright searchlights are to be used. Entry into an area of ice, if possible, should be from the leeward side of the area as here the ice will be less compacted. The sea state will also be calmer here and entry into the ice should be made at a right angle to its edge and at a slow speed to avoid damage to the ships hull.
The ship must be in very good working condition with special reference to the condition of the hull, machinery, steering gear and any other important equipment to the safe operation of the ship.. The ships bunkers and stores must be adequately stocked for the voyage and also in case the vessel was to become stranded in the ice. The vessels maneuvering characteristics, draught, the immersion of the propellers and rudders as well as the experience of the Master and Deck Officers in navigating in Ice must all be fully considered and be deemed appropriate and adequate for navigation in ice. The passage plan used must take into account all of the latest meteorological reports for the area to be transited.
When navigating in ice the most important procedures to be followed are:
- Keep moving. A vessel moving too slowly may become beset in the ice. The speed of the vessel should be enough that headway and control over the vessel can be maintained.
- Excess speeds must be avoided as this will inevitably cause damage to the vessel
- The vessel must preferably move with the movement of ice, if any, and not against it
If within an area where there is a very high concentration of ice, anchoring is to be avoided. This is because if ice begins to build up on the vessel due to the wind the anchor cable and windlass will become strained under the force of the moving ice.
Electronic aids to navigation may become affected by ice. Antennae’s may become covered in ice or snow, leading to their malfunction and therefore hindering communication abilities. The radar scanners may become obstructed or may even become fully covered in ice or snow deeming the radar scanners out f service until the ice or snow build up on the scanners is removed. The echo sounder may be affected if ice builds up n the hull of the vessel. Speed log equipment that uses pressure tubes or impellers may become damaged if ice passes across the hull. The gyro compass should be regularly checked for errors as frequent course alterations in areas of ice and impacts with the ice itself can introduce errors to the gyro compass.
Charts used for navigation map out land without the presence of ice or snow. The appearance of landmarks or coastline covered in snow and ice may well differ from that depicted on the chart. For example pack ice may be mistaken for coastline when observed both visually and by radar, referencing the chart could highlight this error to the OOW as the observations would not match what is charted. Headlands can change dramatically if an iceberg grounds close by to them. The changes in the land in relation to the information charted about the land can cause large errors in position if the OOW uses visual and radar position fixing techniques such as radar ranges and bearings from headlands or from visual bearings from distinct landmarks. The OOW must bear this in mind when considering techniques to use to cross check his/her position. Celestial fixes are also affected whilst navigating in ice as false horizons may be observed due to the refraction and mirage caused by ice on the horizon. Celestial fixes may not be possible at all where the horizon is completely covered by ice and snow.
Floating aids to navigation such as buoys may become a drift due to the force of the ice breaking their moorings or they may move position due to their moorings dragging. If snow and Ice build up on them they may become hidden and may even be removed by local authorities throughout the season when ice is present. The OOW must bear this information in mind If floating navigational aids are used within the passage plan so as he/she can navigate with caution in such areas. Sectored lights are also affected in areas of ice as frost, snow or ice on the lens may change the visibility sector of the light. If positively identified, even though the sector of the light may be inaccurate, they can still be used to take bearings and fix the vessels position. They should still be used with caution and if other means of position fixing is available then they should be used over these.
Lighthouses and beacons are very useful to the OOW for confirming the vessels position but in areas of ice the use of them is hindered as snow and ice can affect the appearance of the structure of such landmarks and may even hide them from sight completely. The range of the lights in the lighthouses and beacons will also be affected by ice and snow in and around the lens.
Radar, when navigating in areas of ice, must be continuously operated at a 6 mile range (quoted from ‘Navigation Advanced for Mates and Masters’ by Capt. Nadeem Anwar). At regular intervals the range should be increased to scan at a longer range to detect larger pieces of ice afloat before they present an immediate danger to the vessel. The OOW should bear in mind that even though radar is a very useful tool in detecting the presence of ice no echo does not mean that there are no pieces of ice in the vicinity. This is because icebergs come in many different shapes. The size and inclination of the surface being reflected and its distance away from the vessel will determine of an echo is received or not. If in calm waters ice is likely to be detected but if snow, rain storms or high winds occur the OOW may have to increase the rain and sea clutter controls to suppress the echoes received from the precipitation and sea state. This will lead to small ice targets and potentially even larger ice targets being undetected due to the circumstances and conditions. The OOW must bear this in mind when using the radar for navigation and ice detection.
Ice Accretion
Sub-freezing air temperatures coupled with strong winds are the causes the precipitation in the air and sea water in the form of spray to freeze on the open decks and structure of the vessel. If in such conditions to ensure the safety of the vessel the OOW must firstly ensure that he/she steers to warmer conditions or seek out shelter. Putting the head into the wind and reducing the speed will reduce the amount of spray coming onto the ship and will therefore decrease the rate of ice accretion. It is also possible to decrease the rate of ice accretion by run before the wind at the ships minimum speed at which she can maintain steerage.
If after completing the actions stated above ice is still accumulating on the ships structure the ice must be physically removed. This is because the build up of ice on the ships structure causes the stability of the vessel to deteriorate and if the amount of ice on the vessel becomes enough the vessel may capsize.
Actions to be taken if the ship becomes beset within the ice
If a ship becomes ‘beset’ in ice (where the ship is stuck in the ice) the propeller should be kept turning slowly so as to keep it clear of ice and icebreaker assistance should be requested as soon as possible to do so. If Icebreaker assistance is not available then the ship may be freed by going from full ahead to full astern whilst going from hard over to port and starboard on the rudders. Altering the trim and heel of the ship may also aid in freeing the ship from the ice.
Anchors can be used to free the ship from the ice by either (quoted from Navigation Advanced for Mates and Masters’ by Capt. Nadeem Anwar’):
- Laying anchors towards each beam on the ice and attempting to move the bow
- By placing an anchor on ice astern and using the engine astern, to move the ship astern
How to work with Icebreakers
The Master of the Icebreaker will be in command of the operation. As the vessel under escort the position of the start of the service should be confirmed and the route and speed ordered by the Icebreaker must be followed. The Icebreaker will create a path for the vessel to follow through the ice and this route must be followed very closely. If the Icebreaker were to stop suddenly, the escorted vessel should stop by either ramming into the ice or going astern on her engines to stop. Towing gear must be rigged as the Icebreaker may tow the escorted vessel through the ice. Any signals given by the icebreaker must be followed immediately.
The distance between the Icebreaker and the escorted vessel is decided with reference to the stopping distance of the vessel under escort (minimum distance) and the ice conditions which depict how quickly the channel will reseal as the icebreaker opens the channel up (this will determine the maximum distance between the vessels).
Bibliography
The Mariners Handbook
Reeds Maritime Meteorology 3rd edition
Navigation Advanced for Mates and Masters’ by Capt. Nadeem Anwar
