Masters of icebreakers are highly skilled and experienced in the specialist fields of ice navigation, icebreaking and ice escorting. It is therefore the Master of the icebreaker who directs any ice escorting operation.
Icebreakers use air reconnaissance, when available, to locate leads and open water. Some carry helicopters which are able to guide ships, by direct communication, along the best routes through the ice.
Escorted vessels must:
Follow the path cleared by the icebreaker and not venture into the ice on their own;
Have towing gear rigged at all times.
Have Officers on the bridge thoroughly acquainted with the Icebreaker Signals given in The International Code of Signals.
Acknowledge and execute promptly signals made by the icebreaker, whether by RT, light or sound.
After requesting icebreaker assistance, a ship must maintain continuous radio watch, and keep the icebreaker informed of any change in her ETA at the position where escorting is to commence.
When an icebreaker is breaking a channel through large heavy floes at slow speed, the channel will be about 30-40 per cent wider than the beam of the icebreaker. If, however, the ice is of a type which can be broken by the stern wave of the icebreaker proceeding at high speed, the width of the channel may be as much as three times the icebreaker’s beam.
In the channel there may be pieces of ice and small floes which the icebreaker has broken off the floes at the sides of the channel. These may greatly reduce the speed of a ship following the icebreaker, or may even block the channel.
Rams sometimes project into the channel from old ice. A ship unable to keep off the ice should request the icebreaker to widen the channel. But in the narrow channel left by an icebreaker in heavy ice, rams are less likely to be encountered.
Distance between ships
The Master of the icebreaker decides on the minimum and maximum distances that a ship should keep from the icebreaker. The minimum distance is determined by the distance the ship requires to come to a complete stop after reversing her engines from full ahead to full astern. The maximum distance depends on the ice conditions and the distance the channel will remain open in the wake of the icebreaker.
If the escorted ship, cannot maintain the distance ordered, the icebreaker should be informed at once. In ice concentrations of 7/10 and less, a ship can usually keep station on the icebreaker with little difficulty. With an ice concentration of 10/10, however, the track will tend to close quickly behind the icebreaker necessitating a very close escort distance. If such ice is under pressure, the distance must be reduced to a few metres since the channel will be quickly covered with ice, leaving only a small lead astern of the icebreaker narrower than her beam. If there is considerable pressure, progress may be impossible.
To force a passage through large floes and ice fields, the icebreaker may require to increase speed to strike the ice and crush and break it ahead of her. A ship following her must then watch the distance carefully and try to enter the channel made up the icebreaker before it closes.
Before entering the ice the Master of the icebreaker will decide on the route to be taken. When course is altered, an escorted ship must follow precisely in the wake of the icebreaker. Alterations of course by the icebreaker are made as gradually as practicable. When sharp turns are made, a ship following the icebreaker is liable to swing into floes at the side of the channel, or to get beset.
The speed of an escorted ship is ordered by the icebreaker. In open ice a speed of 6-7 knots can be expected to be maintained, but only if it is certain that the ship will not collide with the floes. A useful rule of thumb is that 8 knots can be maintained in an ice concentration of 4/10 and that the speed will be reduced by 1 knot for each additional 1/10 of concentration. However, thickness and hardness of the ice, snow cover, puddling and ice under pressure may need to be taken into consideration in addition to the ice concentration. In close ice, when the escorting distance is reduced, a speed of no more than 5 knots should be attempted.
When an icebreaker comes to a standstill and is unable to make farther progress without coming astern, she shows and sounds the appropriate signals. These signals should be treated with extreme urgency. Engines should immediately be put astern and the rudder used to reduce headway.
If a single-screw ship suddenly goes astern while passing through a narrow channel through ice, she may slew and damage her propeller and rudder on the ice.
To avoid collision with a ship ahead it is often preferable to ram the ice on one side of the channel if it is sufficiently thin to embed the bow without damage rather than risking going astern.
Caution. Due to unexpected conditions or in emergency an icebreaker may stop or manoeuvre ahead of an escorted ship without any warning signal.
All icebreakers are fitted with towing winches with a towing wire reeled on each winch drum. Each towing wire, which has at it end an eye and a hauling-in pendant, is led over an indentation in the stern. The winches are sited as far forward as possible to minimise the vertical angle of tow, and to allow the stem of the ship being towed to be hove close into the indentation in the icebreaker’s stern.
Icebreakers tow at either long or short stay. When certain icebreakers tow at short stay, the towed vessel is hauled close-up into an indentation or yoke at the icebreakers stern, and for them, this is the most usual method, particularly when the ice is uneven and the icebreaker’s speed varies. Certain vessels, however, because of their size or the construction of their stem, can only be towed at long stay.
When an icebreaker decides to tow, the assisted ship must immediately prepare to take on board and secure quickly the towing wires, particularly if there is ice screwing or ice pressure. Heaving lines passed to the after deck of the icebreaker are used to bring inboard the hauling-in pendants of the towing wires. These are brought to the escorted ship’s capstan, so that the eyes of the towing wires can be hauled aboard and secured. When the towing wires are fast, the icebreaker is informed and the forecastle cleared of all personnel.
When towing, the icebreaker decides at what speed the towed ship’s engines should be run. The towed ship’s rudder must be used to assist the icebreaker in holding her course and in her other manoeuvres.
Casting off the tow must be done without delay, particularly if towing from the ice into a heavy sea.
Breaking ships out
Then an escorted ship becomes beset, she should normally keep her engines moving slowly ahead to keep ice away from the propellers. In thin ice, the icebreaker usually comes astern along the channel and cuts out ice on. either bow of the ship. The icebreaker then goes astern close along the whole length of the lee side of the beset ship, and then goes ahead, simultaneously ordering the ship to follow her.
In heavier ice, ships can usually be broken out by the icebreaker turning through 180°, going back to the beset ship and passing close aboard her leeward side. The icebreaker then turns through 180° astern of her, and returns along either, her leeward side to thin out the ice or her windward side to relieve pressure on that side, at the same time ordering the ship to follow her.
An alternative method, also used for a ship beset when proceeding independently, is as follows. The icebreaker approaches the beset ship on either quarter, passes along her side, and crosses ahead of her at an angle of between 20° and 30° to the beset ship’s course. In moderate winds, the manoeuvre may be made on either side: in strong winds, the side will be determined by which vessel is most influenced by the wind. Having crossed ahead of the ship, the icebreaker goes astern to crack any floe fragments left near the beset ship’s stem, and then goes ahead ordering the beset ship to follow, keeping in her propeller wash.
If several vessels are to be assisted at the same time, a convoy will be formed. The sequence of ships in the convoy and their distance apart will be ordered before entering the ice by the Master of the icebreaker. Particular attention must be paid to maintaining the distance ordered: it will vary with the ice conditions. If a ship’s speed is reduced, the ship astern must be informed immediately. Ships ahead and astern, as well as the ice, must be carefully watched. Light and sound signals made by the icebreaker must be promptly and correctly repeated by ships in the column in succession.