PREVIOUS |  TABLE OF CONTENTS |  NEXT

29. Ice horns and other exterior appendages

29.1 An ice horn is a device fitted aft of a rudder that is designed to protect it from ice impact when the ship is moving astern.

29.2 Ice horns must be fitted on all ships unless other means are provided to protect the rudder and entire steering system from ice loads when going astern.

29.3 Ice horns must be designed to provide protection to the rudder for two degrees either side of the centreline.

29.4 Ice horns must project below the top of the rudder for a distance of 0.5 ´ VP or 0.5 metres whichever is the greater, where VP is the vertical height of the design ice load from section 14.2.

29.5 The ice horn must be designed to withstand within the elastic range, the design loads determined in this paragraph at all vertical levels.

29.6 The lateral design loads (IKTDL) for an ice horn is determined from the formula:

meganewtons

where:
"CF" is a factor for the Arctic Class from Table 3,

"AF" is a factor equal to 0.5 ,

"VP" is the vertical height of the design ice load from paragraph 14.2 but not greater than the depth of the ice horn,

"IKL" is the length of the ice horn at the level in question, and

"PAV" is the design pressure obtained from Table 6, with the design parameter (DPT) obtained from the formula:-

where
"C" is the chord of the ice horn at the level in question, and

"LDL" is the horizontal length of the design load determined according to section 14.

29.7 The longitudinal design load (IHLDL) for an ice horn is determined from the formula:

where:
"CF" is a factor for the Arctic Class from Table 3,

"AF" is a factor equal to 1.0 ,

"VP" is the vertical height of the design ice load from section 14.2 but not less than the depth of the ice horn,

"IHT" is the thickness of the horn, and

"PAV" is the design pressure obtained from Table 6, with the design parameter (DPH) obtained from the formula:-

where
"IHT" is the thickness of the ice horn and

"LDL" is the horizontal length of the design load determined according to section 14.1.

29.8 Any other exterior appendage such as ice knives, bilge keels etc. must be designed such that if they are damaged that they do not rupture the shell plating or otherwise damage the internal stiffening. They must be designed to safely resist the same ice loads as the area supporting them. Additional local stiffening of the shell and supporting structure is to be arranged to absorb the concentrated loads that can be applied when the design ice load is applied to the appendage.

30. Steering systems ^

30.1 The entire steering system, comprising rudder, pintles, rudder stock, steering gear and steering gear mounts must be designed so that the largest load that may be applied to the rudder from the ice loads developed in section 27 will not exceed the elastic material yield level. The design conditions must include the case where the rudder is forced hard over against the stops, and the rudder stops shall be designed to be within their elastic limits.

30.2 Steering systems must be fitted with physical rudder stops to protect the steering gear and rudder stock when the rudder is forced hard over by ice.

30.3 The physical stops required in paragraph 30.2 must be fitted such that protection is provided two degrees before maximum travel of the steering gear, both Port and Starboard.

30.4 Hydraulic steering systems must be designed for the pressures created when

• the pressure created when the rudder is forced over by ice from the centreline position against the physical stops in 0.1 seconds, and
• a pressure 1.2 times the pressure at which
• the quick acting pressure relief valve required under paragraph 30.5 is set, or
• the bursting pressure of the bursting disc fitted according to paragraph 30.8.

30.5 Except where a bursting disk is fitted complying with paragraph 30.9, every hydraulic steering system must be fitted with a quick acting pressure relief valve having a response time of not more than 10 milliseconds.

30.6 The rudder stock must be designed for a torque of not less than 1.2 times the torque that occurs at

• the setting of the quick acting pressure relief valve required under paragraph 30.5, or
• the bursting pressure of the bursting disc fitted according to paragraph 30.9.

30.7 Where one pressure relief valve is fitted it must be set to not less than 1.25 times the normal working pressure of the system.

30.8 Where the fast acting pressure relief valve required in paragraph 30.5 is fitted in parallel with a relief valve fitted according to Recognized Standards for open water navigation the fast acting relief valve should be set at a pressure 15% higher.

30.9 A bursting disc system may be fitted in lieu of a fast acting relief valve if

• it is fitted in parallel with a relief valve fitted in accordance with Recognized Standards for open water navigation,
• the system is installed in duplicate on each steering gear,
• with isolation valves installed so that only one disk will rupture at any one occasion
• two spare disks are available for installation, and
• means are provided for quick repriming of the system.

30.10 Where an ice horn is fitted, the steering system must be designed such that the rudder is centered automatically immediately before the ship goes astern when the ship is operating in the ice breaking mode. An audible and visual alarm is to be fitted in the wheel house to indicate that the rudder is moving automatically to the central position. An emergency override of the automatic centring mechanism must be fitted.

30.11 Where multiple rudders are fitted, they shall be operated by independent steering mechanisms, and shall not be mechanically connected together.

31. Structural monitoring system ^

A structural monitoring system is required for category 2, 3 and 4 ships. To provide the necessary information to the crew and to record it, the following minimum system is required. The purpose of the information provided to the crew is to enable them to restrict the ramming process so the loads developed are within the structural capability of the ship.

31.1 Each ship required to be fitted with a structural monitoring system (system) shall have the system designed and engineered for operation in the worst anticipated environmental conditions .

31.2 The system must be self contained, and arranged to operate from both the main and emergency electrical supplies.

31.3 The system must maintain a permanent record of all events that approach within 10 per cent of the warning and alarm limits with a window from 5 seconds before to 10 seconds after the event being recorded. The record of all events recorded shall be sent to Ship Safety - Prairie & Northern Region, not less than 30 days before the expiry of the Arctic Pollution Prevention Certificate. Together with each record of events supplied there must be a summary voyage log, giving details of the approximate geographical location, weather, sea and ice conditions at the time of each main event recorded. A statistical and structural analysis may be required to be provided for those alarm events recorded.

31.4 The determination of the warning and alarm limits and the exact location of monitoring gauges must be carried out for each vessel by means of a finite element analysis of the structure or other suitable means. Audible and visual signals giving indication of warning and alarm levels must be given on the navigating bridge.

31.5 Each system must be calibrated on initial installation, yearly, and as necessary between the yearly calibrations. Each system must always be maintained in an operating condition.

31.6 The system must contain as a minimum, two accelerometers in the bow, four long-base deck gauges to measure hull girder loads, and four local plate or frame strain gauges in the shoulder area of the bow area. The hull girder strain gauges are to be arranged to measure the longitudinal bending stress at a position as close as possible to that where it can be expected to be a maximum.

31.7 The system should comply with the requirements for classification society notations such as Lloyd's Register of Shipping - SEA.

32. Submission and approval of plans etc. ^

32.1 Plans shall be submitted for examination for each ship, or series of sister ships, in not less than four copies each, of which one copy of each plan will be returned. Plans shall be submitted for examination for any modifications.

32.2 All plans must be accompanied by copies of the necessary engineering calculations to demonstrate compliance with the Standards.

32.3 Plans must be in adequate detail to fully describe the intended structure. They shall be submitted in either English or French. They shall be of adequate clarity for micro-filming. They must fully detail the size of all welds or other means of connection.

32.4 Mill certificates for all structural steel shall be made available to the pollution prevention officer during construction, and for any new material incorporated at the time of any subsequent repairs or changes to the structure.

32.5 Special care is to be taken during the design and construction process to ensure that fatigue will not lead to premature failure of any part of the structure under the design loads in this Standard.

32.6 Special attention to fatigue is to be given where scantlings are reduced by the use of higher tensile steels. Detail design particulars are to ensure that notches, and other such stress risers are eliminated, by means of having adequate radii at edges or similar techniques.

33. Inspection and construction standards ^

33.1 The owner must ensure during construction that adequate quality control measures are carried out. Compliance with the International Standards Organization (ISO) 9000 series of standards will be accepted as demonstrating that adequate quality control measures are in place. An assessment of the yard standards used may be required to verify that the workmanship is acceptable.

33.2 The owner must make adequate arrangements for the structure to be inspected by a pollution prevention officer or an authorised surveyor of a recognized classification society during construction, repair or modifications.

33.3 On completion of construction, the owner must make arrangements for a pollution prevention officer to inspect the structure and make such tests as are necessary to verify the quality of the structure. All defects found shall be repaired before any certification may be issued.

33.4 After any damage affecting the structural capability of the ship to resist ice loads or other systems required by this Standard, and on completion of repairs to damage or modifications to the structure or any other system required by this Standard, the owner must make arrangements for their inspection, and re-issuance or re-validation of any certification or other documentation.

33.5 All welding must be carried out by qualified welders, and in accordance with approved procedures .

33.6 The final layer of the internal coating of all tanks, and the final layer of all external coatings of the hull should be of a light colour in order to facilitate in-service inspections. It is recommended that the different layers of such coatings are made in contrasting colours so that holidays in the application of the coatings and any breakdowns in service can readily be detected.

34. Maintenance of the structure ^

34.1 The continuing certification of the structure in the original category is contingent on the structure being maintained in good condition. The condition of internal and external coatings protecting against corrosion will also be inspected.

35. Maintenance of certification ^

35.1 If in practice, the ship is found to be inadequately powered, or otherwise unsuitable for operation at the class designated, Ship Safety may reduce the classification, or require such other measures as are necessary to obtain an equivalent level of safety.

36. Design for accessibility ^

36.1 All spaces shall be arranged for their safe inspection and accessibility. Hand rails and guard rails shall be provided as necessary to prevent falls. Ladders, rungs or stairways shall be provided when a vertical access in excess of 600 mm is required.

36.2 For access through horizontal openings, hatches or manholes, the dimensions should be sufficient to allow a person wearing a self-contained air-breathing apparatus and protective equipment to ascend or descend any ladder without obstruction and also to provide a clear opening to facilitate the hoisting of an injured person from the bottom of the space. The minimum clear opening should be not less that 600 mm by 600 mm. In all spaces, ladders or other arrangements as necessary shall be provided to allow a safe vertical ascent and descent below the access openings.

36.3 For access through vertical openings or manholes, providing passage through the length and breadth of the space, the minimum clear opening should be not less than 600 mm by 800 mm at a height of not more than 600 mm from the bottom shell plating unless gratings or other footholds are provided. All opening in vertical openings or manholes shall have hand grips above the openings on each side, where the opening is located more than 600 mm above the horizontal surface from which passage is made.

36.4 Smaller openings may by accepted in special circumstances .

36.5 Plans indicating access routes through all tanks and void spaces are to be kept on board the vessel, and special care is to be taken during construction to ensure that the installations of pipes, conduits or other items does not render any part of the structure inaccessible for inspection.

36.6 Where the space permits, the vertical access in tanks, voids and other compartments shall be arranged by means of sloping stairways and not vertical ladders.

PREVIOUS |  TABLE OF CONTENTS |  NEXT