General
Ice is an obstacle to any ship, even an icebreaker, and the inexperienced Navigation Officer is advised to develop a healthy respect for the latent power and strength of ice in all its forms. However, it is quite possible, and continues to be proven so, for well-found ships in capable hands to navigate successfully through ice-covered waters.
The first principle of successful ice navigation is to maintain freedom of manoeuvre. Once a ship becomes trapped, the vessel goes wherever the ice goes. Ice navigation requires great patience and can be a tiring business with or without icebreaker escort. The open water long way round a difficult ice area whose limits are known is often the fastest and safest way to port, or to the open sea when leaving a port.
Experience has proven that in ice of higher concentrations, four basic ship handling rules apply:
1. keep moving – even very slowly, but try to keep moving;
2. try to work with the ice movement and weaknesses but not against them;
3. excessive speed almost always results in ice damage; and
4. know your ship’s manoeuvring characteristics.
WARNING
EXCESSIVE SPEED IS THE MAJOR CAUSE OF DAMAGE TO SHIPS BY ICE.
Superstructure Icing
Superstructure icing is a complicated process which depends upon meteorological conditions, condition of loading, and behaviour of the vessel in stormy weather, as well as on the size and location of the superstructure and rigging. The more common cause of ice formation is the deposit of water droplets on the vessel’s structure. These droplets come from spray driven from wave crests and from ship-generated spray.
Ice formation may also occur in conditions of snowfall, sea fog, (including Arctic sea smoke) a drastic fall in ambient temperature, and from the freezing of raindrops on contact with the vessel’s structure. Ice formation may sometimes be caused or accentuated by water shipped on board and retained on deck.
Vessel icing is a function of the ship’s course relative to the wind and seas and generally is most severe in the following areas: stem, bulwark and bulwark rail, windward side of the super- structure and deckhouses, hawse pipes, anchors, deck gear, forecastle deck and upper deck, freeing ports, containers, hatches, aerials, stays, shrouds, masts, spars, and associated rigging. It is important to maintain the anchor windlass free of ice so that the anchor may be dropped in case of emergency. Constant spray entering the hawse pipes may freeze solid inside the pipe, also anchors stowed in recessed pockets may freeze in place, both conditions not letting the anchor go. It is good practice in freezing spray to leave anchors slightly lowered in the hawse pipe in order to free them from ice accretion when needed. It is also advisable to maintain securing claws in place in case of slippery brakes, so that the anchors can be readily released in the event of a power blackout.
Superstructure icing is possible whenever air temperatures are – 2.2°C or less and winds are 17 knots or more. It is very likely to take place when these conditions occur at the same time.
In fresh water such as the Great Lakes and St. Lawrence River superstructure icing will occur at 0°C and below, and accumulate faster than in salt water conditions.
Generally speaking, winds of Beaufort Force 5 may produce slight icing; winds of Force 7, moderate icing; and winds of above Force 8, severe icing. Under these conditions, the most intensive ice formation takes place when wind and sea come from ahead.
In beam and quartering winds, ice accumulates more quickly on the windward side of the vessel thus leading to a constant list which is extremely dangerous as the deck-immersion point could easily be reached with a loaded vessel.
The effects of freezing spray can be minimized by slowing down in heavy seas to reduce bow pounding, running with the sea, or seeking more sheltered sea conditions near-shore or in sea ice.
Signs Of Ice In The Vicinity
When steaming through open water, it may be possible to detect the approach of ice by the following signs:
(a) Ice blink: this is a fairly reliable sign and may be the first indication that an ice field is in the vicinity. It can usually be seen for some time before the ice itself is visible and appears as a luminous reflection on the underside of the clouds above the ice. Its clarity is increased after a fresh snowfall. On clear days, ice blink is less apparent but may appear as a light or yellowish haze which would indicate the presence of ice. Ice blink can sometimes be detected at night, either from the reflection of moonlight, or from the ambient starlight in clear weather.
(b) The sighting of small fragments of ice often indicates that larger quantities are not far away.
(c) Abrupt moderation of the sea and swell occur when approaching an ice field from leeward.
(d) The onset of fog often indicates the presence of ice in the vicinity.
(e) On a clear day there may be abnormal refraction of light causing distortion in the appearance of features. Although the ice field will be seen at a greater distance than would normally be possible without refraction, its characteristics may be magnified out of all proportion – it may even appear as giant cliffs of ice in the far distance, with breaks between them where the open water lies.
The following are signs of open water:
(a) Water sky: dark patches on low clouds, sometimes almost black in comparison with the clouds, indicate the presence of water below them. When the air is very clear this indication is less evident. When iceblink is visible at night, the absence of blink in some sectors of the horizon may indicate open water but cannot be assumed to be water sky.
(b) Dark spots in fog give a similar indication, but are not visible for as great a distance as thereflection on clouds.
(c) A dark bank on a cloud at high altitude indicates the presence of patches of open water below,which could lead to larger areas of open water in the immediate vicinity.
Navigation In Ice
Experience has shown that non-ice-strengthened ships with an open water speed of about 12 knots can become hopelessly beset in heavy concentrations of relatively light ice conditions, whereas ice strengthened ships with adequate power should be able to make progress through first-year ice of 6/10 to 7/10 concentrations. Such ships are often able to proceed without any assistance other than routing advice.
In concentrations of 6/10 or less, most vessels should be able to steer at slow speed around the floes in open pack ice without coming into contact with very many of them.
Entering the Ice
The route recommended by the appropriate reporting system is based on the latest available information and Masters are advised to adjust their course accordingly. The following notes on ship-handling in ice have proven helpful:
(a) Do not enter ice if an alternative, although longer, open water route is available.
(b) It is very easy and extremely dangerous to underestimate the hardness of ice.
(c) Enter the ice at low speed to receive the initial impact; once into the pack, increase speed gradually to maintain headway and control of the ship, but do not let the speed increase beyond the point at which she might suffer ice damage. Particular attention should be paid to applied power in areas of weak ice or open leads, pools, etc. where the speed might increase unnoticed to dangerous levels if power is not taken off.
(d) Be prepared to go “Full Astern” at any time.
(e) Navigation in pack ice after dark should not be attempted without high-power searchlights which can be controlled easily from the bridge; if poor visibility precludes progress, heave to in the ice and keep the propeller turning slowly as it is less susceptible to ice damage than if it were completely stopped, blocks of ice will also be prevented from jamming between the blades and the hull.
(f) Propellers and rudders are the most vulnerable parts of the ship; ships should go astern in ice with extreme care, and always with the rudder amidships. If required to ram ice when brought to a halt, ships should not go astern into unbroken ice, but should move astern only in the channel previously cut by their own passage.
(g) All forms of glacial ice (icebergs, bergy bits, growlers) in the pack should be given a wide berth, as they are current-driven whereas the pack is wind-driven. Large features of old ice may be moving in a direction up-wind or across wind according to the direction of the current.
(h) Wherever possible, pressure ridges should be avoided and a passage through pack ice under pressure should not be attempted. The ship may have to be stopped in the ice until the pressure event is ended.
(i) When a ship navigating independently becomes beset, it usually requires icebreaker assistance to free it. However, ships in ballast can sometimes free themselves by pumping and transferring ballast from side to side, and it may require very little change in trim or list to release the ship, especially in high-friction areas of heavy snow-cover.
SHIP HANDLING TECHNIQUES IN ICE
Manoeuvres in Different Ice Conditions
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.
Before Entering the Ice
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.
The following conditions must be met before a vessel enters an ice field:
(a) Follow the route recommended by the Ice Navigator. This route is based on the latest available information and Masters are advised to adjust their course accordingly if changes are recommended during the passage.
(b) Extra lookouts must be posted and the bridge watch may be increased, depending on the visibility.
(c) There must be sufficient light to complete the transit of the ice field in daylight or the vessel must be equipped with sufficient high-powered and reliable searchlights for use after dark.
(d) Reduce speed to a minimum to receive the initial impact of the ice.
(e) The vessel should be at right angles to the edge of the pack ice at entry to avoid glancing blows and the point of entering the ice must be chosen carefully (see Figure), preferably in an area of lower ice concentration.
(f) The engine room personnel should be briefed fully as to the situation and what may be required of them, as it may be necessary to go full astern at any time, and engine manoeuvres will be frequent as speed is constantly adjusted.
(g) The ship should be ballasted down to ice draft, if appropriate, or to such a draft that would offer protection to a bulbous bow, rudder, or propeller (as applicable).
(h) The ship should be fitted with an internal cooling system for use in the event that the main engine cooling water intake becomes clogged with slush ice.
After Entering the Ice
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.
When navigating in ice, the general rule is:
- Use the pack to its best advantage. Follow open water patches and lighter ice areas even if initially it involves large deviations of course.
- In limited visibility, beware following an open water lead at excessive speed, it may be the trail of an iceberg.
- 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.
Turning in Ice
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.
WARNING: AVOID TURNING IN HEAVY ICE – SEEK LIGHTER ICE OR OPEN WATER POOLS.
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 danger 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
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.
In recent years “double-acting” ice strengthened vessels have been developed which are designed to break ice while moving astern in order to protect their bulbous bows, but only this type of specially designed vessel should attempt such manoeuvres.
The ship should move at dead slow astern and the rudder must be amidships (See 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.
WARNING: AVOID BACKING IN ICE WHENEVER POSSIBLE. IF YOU MUST MOVE ASTERN, DO SO WITH EXTREME CAUTION AT DEAD SLOW.
Precautions to Avoid Becoming Beset
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.
WARNING: 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 (See 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.
Freeing a Ship Beset
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:
(a) Go ahead and astern at full power while alternating the helm from port to starboard, which has the effect of levering the ice aside. Care must be taken when going astern to ensure that no ice goes through the propeller(s), or if the vessel frees itself that it does not make sternway into any heavy ice. In vessels with twin propellers, they should be alternated with one ahead and one astern for a few minutes, then each changed to the opposite direction, slewing the stern from side to side to create a wider opening in the ice astern.
(b) Alternate the ballast to port and to starboard to list the ship and change the underwater shape. This method should only be done with knowledge of the possible consequences of an exaggerated list if the ship comes free quickly.
(c) Alternate filling and emptying of the fore and after peak tanks is a safer manoeuvre than using the ballast tanks, but it is usually only effective in changing the trim for the bow to get a better angle of attack on the ice ahead, or for the propellers to be given a better grip by greater submersion. It can also be effective in extracting from a ridge, by raising the bow so that the ship slides backwards as the bow is raised.
(d) In smaller ships it may be possible to swing weights over the side suspended on the ship’s cranes or lifting gear to induce a list and break the ship free. This method should only be used with knowledge of the possible consequences if the ship comes free quickly (see (b) above).
Berthing
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 ( See Figure).
Frequently it is necessary to combine the two techniques (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 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.
WARNING: KEEP THE ENGINE(S) ON STANDBY AT RIVER BERTHS OR STRONG TIDAL AREAS WHERE ICE IS IN MOTION