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This is the ice belt, part of the hull from the bow to approximately the middle of the ship's length on both sides. However, even high-strength ferrous metal is vulnerable in the Arctic seas.
Operation of the first nuclear-powered icebreaker, Lenin, showed that the combined effect of ice and sea water leads to corrosion-erosion of the outer layer. In the first years of operation of the icebreaker, the roughness of the steel skin increases more than tenfold before it stabilises, and this seriously reduces the speed of the ship. To protect the metal from wear and tear, the surface can be coated with a special paint, but the effect is temporary and the paint needs to be restored almost annually.
Material scientists now developed bimetal - clad steel — to solve this problem. Clad sheets are used in various industries for protection against aggressive environments. It is an alternative to single-layer, homogeneous rolled products from expensive alloy steels. The clad steel for the ice belt of a nuclear icebreaker consists of two sheets. The main one - ordinary ferrous metal about 50mm thick - and stainless steel cladding 5mm thick, which comes in to contact with ice and water.
This steel is highly resistant to wear, and the roughness changes only slightly even under the most severe conditions. At first, as an experiment, sheets of clad steel were welded into the ice belt of the hulls of the nuclear-powered icebreakers Arktika, Siberia and Yamal as patches, in those areas where the most intense wear take place during operation. After several years of icebreaker operation, the patches remained smooth, and only the protective paint had worn away while the roughness of the metal around the patches increased markedly.
In general it can be said that rafted, ridged, and rubbled ice present significant impediments to the progress of a ship. Caution should also be used when navigating through level ice with occasional hummocks or rafted areas or inclusions of old ice. Any ship that is not strengthened for operating in ice should avoid large unbroken ice floes, particularly if the ice is deformed by rafts, ridges, or rubble.
When the ice thickness exceeds that in which the ship can make continuous progress, such as when the ship encounters old ice, ridges, rafts, or hummocks , the ship could resort to ramming if the ship's design and structural strength permits. It is important that the ice navigator understands how much impact from the ice the vessel can withstand without suffering damage, and at what speed hull damage is likely to be inflicted by the ice environment currently being experienced.
The influence of snow on ship performance varies directly with snow thickness and snow type, and greatly increases ship resistance. The friction coefficient between snow and a ship's hull varies with the consistency and wetness of the snow; wetter snow has a higher friction coefficient than dry snow. In certain environmental conditions the snow will be quite "sticky" whereas, in others, it will be very dry and brittle.
One rule of thumb suggests that resistance from snow cover can be approximated by adding half the snow thickness to the observed ice thickness and assessing performance in ice of the increased calculated thickness. Resistance in "sticky" snow is very difficult to predict, but it can be very high: equal to, or greater than, the icebreaking resistance. Low friction coatings and hull form are important elements in ship performance in snow-covered ice.
In ramming mode a low-friction hull coating will facilitate extraction astern after each ram, as well as permitting each ram to proceed further ahead than would be possible with a bare steel hull surface.
The features of hull shape that influence manoeuvrability in ice to the greatest extent are length-to-breadth ratio, flare, mid-body, and bow and stern shape. Manoeuvrability is also greatly influenced by ice conditions, such as: thickness, coverage, pressure, and shear zone conditions.
The diameter of a ship's turning circle increases as the thickness of the ice increases. Turning in level ice conditions is generally influenced by the degree of confinement imposed by the surrounding ice.
Steady turns are recommended for most vessels that are not as manoeuvrable as icebreakers, however it is more common for icebreakers to use star or channel breakout manoeuvres as a faster means of turning. These manoeuvres are described in subsection 4. Heeling systems have been demonstrated to be effective for most icebreaking ships, especially in snow-covered ice situations. A ship's performance in ice can be limited by the hull structure's capability to withstand ice impacts.
Different modes of operation and ice regimes will generate different magnitudes of ice impact forces. For example, a ship encountering first-year ice will experience lower impact forces than a ship encountering old ice. A ship — usually an icebreaker - which is required to ram ice features aggressively with the intention of protecting less capable ships or structures will, of necessity, incur higher impact forces to break ice which would damage that which they are protecting.
In terms of overall magnitude, ramming operations generate the largest forces on the ship's structure, and being repetitive, they may cause cumulative damage. Performance enhancing systems are designed to reduce the power necessary for propulsion and to increase the ship's manoeuvrability through ice.
Heeling systems, which roll the ship from side to side and reduce the effect of static friction, are helpful if the ship is stuck in pressured ice, or beached on an ice feature.
The following hull lubrication systems can also reduce resistance and aid manoeuvrability:. Ice is an obstacle to any ship, even an icebreaker, and the inexperienced navigator is advised to develop a healthy respect for the potential strength of ice in all its forms. However, it is quite possible, and continues to be proven so, for well-maintained and well-equipped ships in capable hands to navigate successfully through ice-covered waters.
Masters who are inexperienced in ice often find it useful to employ the services of an Ice Advisor for transiting the Gulf of St. Lawrence in winter or an Ice Navigator for voyages into the Arctic in the summer. The first principle of successful ice navigation is to avoid stopping or becoming stuck in the ice. Once a ship becomes trapped, it goes wherever the ice goes. Ice navigation requires great patience and can be a tiring business, with or without icebreaker escort.
The longer open water way around a difficult ice area whose limits are known is often the fastest and safest way to port or to reach the open sea. For an unstrengthened ship, or for a ship whose structural capability does not match the prevailing ice conditions, it is preferable and safer to take any alternative open water route around the ice even if it is considerably longer.
An open water route is always better than going through a large amount of ice. Any expected savings of fuel will be more than offset by the risk of damage, and the actual fuel consumption may be higher by going through ice, even if the distance is shorter.
Once the ice is entered, speed of the vessel should be increased slowly, according to the prevailing ice conditions and the vulnerability of the ship. If visibility decreases while the vessel is in the ice, speed should be reduced until the vessel can be stopped within the distance of visibility. If in doubt, the vessel must stop until the visibility improves. The potential of damage by ice increases with less visibility.
If the vessel is stopped, the propeller s should be kept turning at low revolutions to prevent ice from building up around the stern. Do not allow the speed to increase to dangerous levels when in leads or open pools within an ice field, or when navigating open pack conditions.
Changes in course will be necessary when the vessel is in ice. If possible course changes should be carried out in an area of open water or in relatively light ice, as turning in ice requires substantially more power than turning in water, because the ship is trying to break ice with its length rather than with its bow, turns should be started early and make as wide an arc as possible to achieve the new heading.
Care must be taken even when turning in an open water area, as it is easy to underestimate the swing of the ship and to make contact with ice on the ship's side or stern: a glancing blow with a soft piece of ice may result in the ship colliding with a harder piece see Figure The ship will have a strong tendency to follow the path of least resistance and turning out of a channel may be difficult or even impossible.
Ships that are equipped with twin propellers should use them to assist in the turn. In very tight ice conditions, a ship sailing independently may make better progress by applying full power and leaving the rudder amidships. This allows her to find the least resistance without any drag from the rudder in trying to maintain a straight course by steering.
If it is not possible to turn in an open water area, the Master must decide what type of turning manoeuvre will be appropriate. If the turn does not have to be sharp then it will be better to maintain progress in ice with the helm over.
When ice conditions are such that the vessel's progress is marginal, the effect of the drag of the rudder being turned may be sufficient to halt the vessel's progress completely. In this case, or if the vessel must make a sharp turn, the star manoeuvre will have to be performed. This manoeuvre is the equivalent of turning the ship short round in ice by backing and filling with the engine and rudder.
Masters will have to weigh the dangers of backing in ice to accomplish the star manoeuvre, against any navigational dangers of a long turn in ice. Care must be taken while backing on each ram that the propeller and rudder are not forced into unbroken ice astern. Backing in ice is a dangerous manoeuvre as it exposes the most vulnerable parts of the ship, the rudder and propeller, to the ice. It should only be attempted when absolutely necessary and in any case the ship should never ram astern.
The ship should move at dead slow astern and the rudder must be amidships Figure If the rudder is off centre and it strikes a piece of ice going astern, the twisting force exerted on the rudder post will be much greater than if the rudder is centred. In the centre position, the rudder will be protected by an ice horn if fitted.
If ice starts to build up under the stern, a short burst of power ahead should be used to clear away the ice. Using this technique of backing up to the ice and using the burst ahead to clear the ice can be very effective, but a careful watch must be kept of the distance between the stern and the ice edge.
If a good view of the stern is not possible from the bridge, post a reliable lookout aft with access to a radio or telephone. Avoid backing in ice whenever possible. If you must move astern, do so with extreme caution at dead slow. The easiest way to avoid being beset is to avoid areas of ice under pressure.
Ice can be put under pressure in several ways. The most common pressure situation occurs when open pack ice closes because of prevailing winds, but it may also occur when tides, currents, or on-shore breezes blow ice onto the shore. Pack ice that has been under pressure for some time will deform, overriding as rafts or piling up as ridges or hummocks. Appearances are deceiving as the sail on a ridge or hummock may be only 1 to 2 metres above the ice cover but the keel could be several metres below.
Any ship that is not strengthened for operating in ice should avoid floes that are rafted or ridged. The danger from becoming beset is increased greatly in the presence of old or glacial ice, as the pressure on the hull is that much greater. When in pack ice, a frequent check should be made for any signs of the track closing behind the ship. Normally there will be a slight closing from the release of pressure as the ship passes through the ice, but if the ice begins to close up completely behind the ship it is a strong sign that the pressure is increasing Figure Similarly, if proceeding along an open water lead between ice and shore, or ice in motion and fast ice, watch for a change in the wind direction or tide as the lead can close quickly.
To free a beset vessel, it is necessary to loosen the grip of ice on the hull, which may be accomplished in several ways, or it may be necessary to wait for conditions to improve:. Ramming is particularly effective when attempting progress through ice that is otherwise too thick to break continuously.
Ramming should not be undertaken by vessels that are not ice-strengthened and by vessels with bulbous bows. Ice-strengthened vessels, when undertaking ramming, should do so with extreme caution. For ships that can ram the ice it is a process of trial and error to determine the optimum distance to back away from the ice edge to build up speed. The optimum backing distance will be that which gives the most forward progress with the least travel astern.
It is always necessary to start with short rams to determine the thickness and hardness of the ice. All ships must pay close attention to the ice conditions, to avoid the possibility of lodging the ship across a ridge on a large floe. Floes of old ice which may be distributed throughout the pack in northern waters, must be identified and avoided while ramming.
Ramming must be undertaken with extreme caution because the impact forces caused when the vessel contacts the ice can be very high.
For ice-strengthened vessels these forces may be higher than those used to design the structure and may lead to damage. However, if the ramming is restricted to low speeds, the risk of damage will be greatly reduced. Abandoning ship in ice-covered waters is possible, if necessary, by landing lifeboats or life rafts on the ice, if the ice is thick enough to take their weight.
Vessels fitted with quick-release drop-lifeboats without davits should never attempt to launch them into ice, but should lower them gently to the ice-surface by using the recovery equipment in reverse.
If the ship can be made sufficiently seaworthy to proceed, an assessment will have to be made of the demands that will be placed on the ship by breaking ice during the remainder of the voyage, as opposed to any risks in waiting for escort. The damaged area should be protected from further impacts by trimming the vessel, although this will have an effect on its ability to break ice.
In ice-strengthened ships, ballasting to minimize flooding can expose the hull above or below the ice belt. Care should be taken that the change in trim does not expose the rudder and propeller s to the ice, but, if it is unavoidable, that any subsequent decision is made with the knowledge of this exposure.
Berthing in ice-covered waters can be, and usually is, a long process, particularly in the Arctic where normally there are no tugs. When approaching a berth in ice-covered waters it is desirable even if this is not the normal practice to have an officer stationed on the bow to call back the distance off the wharf or pier because a variation in ice thickness not observed from the bridge can result in a sudden increase or decrease in the closing speed of the bow and the wharf.
There are a multitude of considerations depending on ship size and berth type, but the aim should be to bring the ship alongside with as little ice as possible trapped between the ship and the dock face.
It may be accomplished by landing the bow on the near end of the dock and sliding along the face similar to landing the bow on the wall entering a lock in the Seaway , or by bringing the bow in to the desired location, passing a stout spring line, and going ahead slowly so that the wash flushes the ice out from between the dock and the ship Figure Frequently it is necessary to combine the two techniques in ships of sufficient manoeuvrability it is possible to clear ice away from the wharf prior to berthing.
Care must be exercised not to damage the wharf by contact with the vessel, or by forcing ice against pilings. The ship itself can be damaged by forcing unbroken floes of hard ice against the unyielding facing of a solid berth. Once the ship is secured, all efforts must be made to keep the ship alongside and not to allow ice to force its way between the ship and the dock.
If the dock is in a river or in a strong tidal area there is nothing that will keep the ship alongside if the ice is moving. The prudent thing to do is to move the ship off the dock before the situation deteriorates. The ice conditions can change quickly when alongside a wharf and, for this reason, it is desirable to keep the engine s on standby at all times. The situation can be alleviated somewhat if there is an icebreaker making a track ahead of the towing icebreaker. The Canadian Coast Guard does not usually engage in towing operations except in emergency situations.
There is a long tradition of this sort of work in the Baltic, though, where icebreakers are specially designed with a notch in the stern and heavy winches and cables to enable the bow of the towed ship to be brought up against the stern of the icebreaker and secured. This towing method is known as close coupled towing and is considered an efficient method of towing in uniform ice conditions. Close-coupled towing techniques which are commonly used by European icebreakers in the Baltic Sea and in Russian waters of the Northern Sea Route, are not used in Canadian waters.
Towing in ice was common in the s and early s in the Beaufort Sea, by anchor-handling supply boats or icebreakers when repositioning drill ships and platforms. Experience has shown that towing in ice requires specialized skills in towing and ice navigation, coupled with appropriate purpose-designed equipment.
The towing equipment must be robust and must allow frequent changes in towline length. The use of shock-absorbing springs or heavy surge chains is recommended.
Bridle arrangements must optimise manoeuvrability to allow the towing vessel and tow to be navigated around heavy ridges and ice floes. It is the recommended practice that the connection between vessels should incorporate a weak link, usually a lighter pendant, which will fail before the tow-line or bridle.
In difficult ice conditions the towline should be kept as short as possible to avoid having the towing-wire pass under the ice floes, due to the weight of the wire and the catenary formed by a longer line.
In freeing a beset tow, the towing vessel can shorten the tow-line to provide some propeller wash to lubricate the tow, but care must be exercised to avoid damaging the tow with heavy ice wash. Towing in ice is a special application not to be undertaken without the benefit of training and experience.
In all attempts at manoeuvring or avoiding ice, it must be remembered that the force of impact varies as the square of the speed. Thus, if the speed of the ship is increased from 8 to 12 knots, the force of impact with any piece of ice has been more than doubled. Nevertheless, it is most important when manoeuvring in ice to keep moving.
The prudent speed in a given ice condition is a result of the visibility, the ice type and concentration, the ice class, and the manoeuvring characteristics of the ship how fast it can be stopped. In situations where an icebreaker is used to prevent ice from colliding with fixed structures, such as drilling platforms, the technique of ice management comes into force.
The icebreaking and offshore supply fleet in the Canadian and U. Arctic has been involved with work to support drilling operations. Icebreakers either try to break up drifting ice before it arrives at the structure or to push and divert the dangerous floes out of the way so that they by-pass the structure.
In ice management, obtaining information about the present and predicted ice conditions is very important, to ascertain the best deployment of the icebreakers. Although a careful lookout will help the ship avoid large ice hazards such as icebergs , there is still a need for the close-range detection of ice hazards, such as small icebergs and old ice floes.
Close-range ice navigation is an interactive process, which does not lend itself to traditional passage planning techniques. Two groups of equipment aid in close-range hazard detection: visual searchlights and binoculars and radar both X- and S-band marine radars and the newer enhanced ice radar systems. Radar can be a great asset in ice navigation during periods of limited visibility, but only if the display is properly interpreted. Ice makes a poor radar target beyond 3 to 4 nautical miles and the best working scale is in the 2 to 3 nautical mile range.
Radar signal returns from all forms of ice even icebergs are much lower than from ship targets, because of the lower reflectivity of radar energy from ice, and especially snow, than from steel. Detection of ice targets with low or smooth profiles is even more difficult on the radar screen, although the radar information may be the deciding factor when attempting to identify the location of these targets under poor conditions, such as in high seas, fog, or in heavy snow return.
For example, in close ice conditions the poor reflectivity and smooth surface of a floe may appear on the radar as a patch of open water, or signal returns from sea birds in a calm sea can give the appearance of ice floes. In an ice field, the edge of a smooth floe is prominent, whereas the edge of an area of open water is not.
The navigator must be careful not to become over-confident in such conditions. In strong winds the wave clutter in an area of open water will be distributed uniformly across the surface of the water, except for the calm area at the leeward edge. Ice within one mile of, and attached to, the shore may appear on the radar display as part of the land itself. The operator should be able to differentiate between the two if the receiver gain is reduced.
Mariners are advised not to rely solely on radar for the detection of icebergs because they may not appear as clearly defined targets. In particular, mariners should exercise prudence when navigating in the vicinity of ice or icebergs. The absence of sea clutter also may indicate that ice is present. Although ridges may show up well on the radar display, it is difficult to differentiate between ridges, closed tracks of ships and rafted ice, as all have a similar appearance on radar.
The effectiveness of marine radar systems will vary with power and wavelength. The optimum settings for the radar will be different for navigating in ice than for open water.
As the radar reflectivity of ice is much lower than for ships or land, the gain will have to be adjusted to detect ice properly.
Generally, high-power radars are preferred and it has been found that radars with 50 kW output provide much better ice detection capability than 25 kW radars. Similarly, 3-centimetre radars x-band provide better ice detail while centimetre radars s-band show the presence of ice and ridging at a greater distance - it is therefore recommended that both wavelengths be used.
Marine radar provides an important tool for the detection of sea ice and icebergs. However, do not rely solely on your radar in poor visibility as it is not certain that radar will detect all types and sizes of ice and it will not differentiate old ice from first year ice. Conventional marine radars are designed for target detection and avoidance. Enhanced marine radars provide a higher definition image of the ice that the vessel is transiting through and may help the user to identify certain ice features.
There are various shipboard marine radar systems enhanced and optimized for ice navigation. Figures 55 to 58 compare images from a conventional x-band radar and an enhanced x-band ice navigation radar used on board a Canadian Coast Guard icebreaker. In the ice navigation radar, the analog signal from the x-band radar azimuth, video, trigger is converted by a modular radar interface and displayed as a bit digital video image x In the enhanced marine radar, the coastline is more clearly defined; icebergs are visible at greater distances, as are the smaller bergy bits and growlers.
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