The Arctic Ice Regime Shipping System (AIRSS)

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3.1 The Ice Regime System

The Arctic Ice Regime Shipping System involves comparing the actual ice conditions along a route to the structural capability of the ship. The basic definition of an ice regime is as follows:

“An ice regime is composed of any mix or combination of ice types, including open water. An ice regime occurs as a region in navigable waters covered with generally consistent ice conditions; i.e. the distribution of ice types and concentrations does not change very much from point to point in this region.” Page 23, TP 9981

Under this system, the decision to enter a given ice regime is based on the quantity of dangerous ice present, and the ability of the vessel to avoid the dangerous ice along the route to (and from) its destination.

Every ice type (including Open Water) has a numerical value which is dependent on the ice category (Class or Type) of the vessel. This number is the Ice Multiplier (IM). The value of the Ice Multiplier reflects the level of danger that the ice type poses to the particular category of vessel.

3.2 Ice Numeral Calculations

For any ice regime, an Ice Numeral (IN) is the sum of the products of:

  1. the concentration in tenths of each Ice Type, and
  2. the Ice Multipliers relating to the Type or Class of the ship in question.

Equation: IN = (Ca x IMa) + (Cb x IMb) + ...


  • IN - Ice Numeral
  • Ca - concentration in tenths of ice type "a"
  • IMa - Ice Multiplier for ice type "a" (refer to the Ice Multiplier Table on either page 11 or page 5 in the AIRSS Standards)

The term(s) on the right hand side of the equation (a, b, c, etc.) are repeated for as many Ice Types and each of their respective concentrations that may be present, including Open Water. Ice Numerals can be calculated from ice conditions as shown in the Canadian Ice Service’s, MANICE / WMO ice “eggs” or data obtained from other sources.

The Ice Numeral is therefore unique to the particular ice regime and ship operating within its boundaries. To use the system, the master or ice navigator needs to identify the ice types and concentrations along the route - information sources are also outlined in Section 4.0.

Note: While doing any Ice Numeral calculation remember that every regime is composed of an aggregate 10/10th’s concentration of various ice types. As an example, if an ice “egg” shows a total concentration of 6/10th’s, remember that the other 4/10th’s is Open Water and should be accounted for in the IN calculation. (Examples are on page 15)

3.3. Linking the Canadian Ice Service Charts to the ‘Ice Multipliers’

The principal concept upon which the Ice Regime System has been developed is that:

“Every ice type (including open water) has a numerical value which is dependent on the ice category of the vessel. This number is called an Ice Multiplier (IM). The value of the Ice Multiplier reflects the level of risk or operational constraint that the particular ice type poses to each category of vessel.” (TP 12259, Page 7)

The Canadian Ice Service’s products, in particular their Tactical, Daily and Weekly Ice Analysis Charts can be used for geographically defining “Ice Regimes” together with actual visual observations. Their ice Codings, or descriptions comply with the World Meteorological Organization (WMO) nomenclature. While using the Arctic Ice Regime Shipping System, a mariner can use an ice analysis chart to calculate an Ice Numeral based upon the ice types, as shown by the codes within the ice ovals or ice “eggs”.

The complete WMO coding, from MANICE (Pages 3-6) has been included below, explaining how the codes from within the ice eggs relate to the Ice Regime System. The following table combines the MANICE material with the Ice Multiplier Table from the AIRSS Standards to clarify how ice chart information can be used to define an ice regime.

Coding for Sea Ice Stages of Development

Description Thickness Code Ice Regime System Comments
Bergy Water, Brash & New Ice < 10 cm 1 Consider it 'Open Water'
Nilas, Ice Rind < 10 cm 2 Consider it 'Open Water'
Young Ice 10-30 cm 3 May appear on Tactical Ice Charts, but never on Daily or Weekly Charts
Grey Ice 10-15 cm 4  
Grey-White Ice 15-30 cm 5  
First-Year Ice ≥30 cm 6 May appear on Tactical Ice Charts, but never on Daily or Weekly Charts (If seen, must assume it's 4• ice.)
Thin First-Year Ice 30-70 cm 7 The code "7" must be considered to be Thin First-Year Second Stage. (This will only affect Type C ships)
First Stage Thin First-Year 30-50 cm 8 Only used in the Baltic Sea
Second Stage Thin First-Year 50-70 cm 9 Only used in the Baltic Sea
Medium First-Year Ice 70-120 cm 1•  
Thick First-Year Ice > 120 cm 4•  
Old Ice   7• A 7• must be considered to be Multi-Year Ice until September 30th
Second-Year Ice   8• Will only appear on ice charts 01 October to the 31st of December
Multi-Year Ice   9• Will only appear on ice charts 01 October to the 31st of December
Ice of land origin   Δ• N/A to Ice Numerals
Undetermined or unknown   X N/A to Ice Numerals

Ice Multiplier Table

Ice Codes
  Ice Multipliers for each Ship Category
Ice Types Thickness Type E Type D Type C Type B Type A CAC 4 CAC 3
7• or 9• Old/Multi-Year Ice   -4 -4 -4 -4 -4 -3 -1
8• Second-Year Ice   -4 -4 -4 -4 -3 -2 1
6 or 4• Thick First-Year Ice > 120 cm -3 -3 -3 -2 -1 1 2
1• Medium First-Year Ice 70-120 cm -2 -2 -2 -1 1 2 2
7 Thin First-Year Ice 30-70 cm -1 -1 -1 1 2 2 2
9 Thin First-Year Ice - 2nd stage 50-70 cm              
8 Thin First-Year Ice - 1st stage 30-50 cm -1 -1 1 1 2 2 2
3 or 5 Grey-White Ice 15-30 cm -1 1 1 1 2 2 2
4 Grey Ice 10-15 cm 1 2 2 2 2 2 2
2 Nilas, Ice Rind < 10 cm 2 2 2 2 2 2 2
1 New Ice < 10 cm " " " " " " "
  Brash (Ice fragments < 2 m across)   " " " " " " "
Bergy Water   " " " " " " "
| | | | Open Water   " " " " " " "
Decayed Ice:
For the following ice types: MY, SY, TFY, and MFY that are Decayed, add +1 to the Ice Multiplier.
Ridged Ice:
For ice floes that are over 3/10ths ‘Ridged’ and in an overall ice concentration that is greater than 6/10ths, subtract 1 from the Ice Multiplier.
Ice Codes:
7•, 6 & 3 are additional Ice Codes, of a more general nature. Code 7• represents Old Ice, which is used until Sept. 30th. Code 6 is First Year Ice, and 3 represents Young Ice, both of which may only appear on Tactical Ice Charts and rarely on the Daily Ice Analysis or Weekly Regional Ice Charts. These three Ice Codes are used when the resolution of digital images or data sets does not distinguish the exact ice thickness. For example; an Ice Type 6 would mean that there could be Ice Types: 4•, 1•, 9, 8 or 7 present in that location in any combination / mixture. 8 and 9 are not used in Canada, (originated in the Baltic Sea) except if ice thickness measurements have been taken. These two rows have been primarily kept on the Table to facilitate an international Ice Regime System in future years. 7 is a popular code that has a thickness of up to 70 cm and must be considered equivalent to Thin First-Year Ice, 2nd Stage as a safety measure. 8• and 9• shall normally appear on ice charts only from 01 October to 31 December.
CAC 1 / CAC 2:
The two highest ship categories, CAC 1 & CAC 2, are designed for unrestricted navigation in the Canadian Arctic.

*Another version of this table can be found in TP 12259.

3.4 Ice Features and Other Factors that Affect Ice Multipliers

3.4.1 Decayed Ice

Currently there is no WMO or MANICE definition of Decayed Ice, however for the purpose of the Ice Regime System, the definition that is in place states:

“Decayed ice: means

  1. Multi-Year ice,
  2. Second-Year ice,
  3. Thick First-Year ice, or
  4. Medium First-Year ice

which has thaw holes formed or is Rotten ice.1

In the past Decayed Ice, because of its difficulty in satellite detection, didn’t appear on any ice chart, other than Tactical Ice Charts that were based upon visual observations. Currently there is research being conducted in this area and during the summer of 1999 Decayed Ice will appear on Daily Ice Analysis Charts and a formal definition is being developed internationally for insertion into the WMO nomenclature.

For Decayed Ice +1 may be added to that ice type’s Ice Multiplier. As an example, if a Type B ship encounters decayed Thick First-Year ice, the Ice Multiplier changes from -2 to -1.

3.4.2 Ridged Ice

Where the total ice concentration in a particular regime is 6/10th’s or greater, and at least 3/10th’s of the area of an ice type (other than Brash Ice2) is deformed by Ridges, Rubble or Hummocking, the Ice Multiplier for that ice type, shall be decreased by 1. The basis for this numeric adjustment is that ridged ice is thicker. If, as an example a Type E ship finds a regime with Ridged Thin First-Year ice, the Ice Multiplier changes from -1 to -2.

3.4.3 Brash Ice

As a result of research obtained during validation studies, loose Brash Ice (not Jammed Brash Barrier or Agglomerated Brash) has been given the same weighting as Open Water i.e. a +2 Ice Multiplier. Within the concept of the Ice Regime System, this form of ice is intended to account for the ice predominately found in well defined icebreaker tracks and because the Ice Regime System is based on safety and not performance, it is possible to have a positive Ice Numeral, while surrounded by Brash and not be able to move.

3.4.4 Trace of Old Ice

On occasion, traces of ice may be reported in ice forecasts or indicated on the left side (outside) of an ice egg. A trace means less than 1/10th ice concentration (MANICE, Page 3-5) and is not required to form part of the Ice Numeral calculation process. If a trace of Old Ice is encountered within a regime, extra caution should be exercised when navigating due to the risk that this form of ice creates. As an illustration of a trace of Multi-Year ice, an Ice Numeral is calculated in Example 3 on page 16.

3.4.5 Strips & Patches

A common notation found on Canadian Ice Service ice charts is the symbol placed either in the top or bottom of an ice egg or if the floe sizes are significant, connecting two eggs indicating Strips & Patches. When using the Ice Regime System, the ice within the Strips or Patches actually forms smaller regimes and they should be treated as such. From a tactical Ice Navigator’s perspective, this type of regime would have to be visually assessed to see if it is possible to transit the area without encountering a negative Ice Numeral. If the orientation of the ice within the regime generally parallels the ship’s base course there should be little difficulty. However, if these features lie across the intended track, depending upon their extent, a transit of this ice regime may not be possible. Particular care may be required in planning a route through this regime. Below is a realistic example:

3/10ths total ice concentration in strips and patches of 9+/10sths concentration. In the strips or patches there will be 6/10ths Old ice in vast floes and 4/10ths thick First-year ice in big floes. These sizes are significant and warrant the uses of two ovals.

A Strips and Patches Example

For more information on Strips and Patches, pages 3-8 and 3-19 of MANICE should be consulted.

3.4.6 Floe Size

The Ice Numeral calculation does not account for floe size3. Depending upon a ship’s size and manoeuvrability, an experienced mariner may know that it is easier to pick a route and safe speed in an ice regime composed of Small Ice Floes (20-100 m) and Very Open / Open Pack ice (1/10th to 6/10th’s) concentrations, compared to a regime with larger floes that may offer a similar Ice Numeral. At this time there is no direct way of quantifying this relationship numerically4 within the Ice Regime System.

3.4.7 CAC 1 and CAC 2 Ships

The two highest ship categories, CAC 1 and CAC 2, are designed to withstand impacts with all Ice Types, and therefore have been excluded from the Ice Multiplier (IM) Table. (TP 12259, Page 4 and TP 9981, Page 25)

3.4.8 Safe Speed

The ship’s speed is a critical aspect of safe ice navigation. At this time speed has not been numerically incorporated as part of the aggregate Ice Numeral calculations within the Arctic Ice Regime Shipping System, but it must be an important consideration for a mariner operating with due caution in ice-infested waters.

A vessel navigating in a regime composed of either Bergy Water or a trace of Old Ice could have an Ice Numeral that is +18 to +20. This high, positive number could create a false sense of security and in turn, create a high risk transit.4 In many ice regimes to which entry is permitted, mariners must be aware that the vessel’s operating speed should cautiously be selected to avoid damaging impacts with dangerous ice, preferably by avoiding it altogether. A ship operated conservatively at low speed will run little risk, while another operated at a higher speed through inexperience could be at significant risk.

Safe speed is a function of the crew’s ability to incorporate: the ship's capability, weather, visibility, radar information, ice pressure and the availability and or lack of other navigational or ice information.

Type D Carrier Damaged in Hudson Strait

This Type D Bulk Carrier was Damaged in Hudson Strait

3.4.9 Ship Under Escort

When under the escort of another vessel, the Master of the escorted ship when calculating the Ice Numeral can take into consideration the track ahead, together with the prevailing conditions in assessing the ice regime for the ship. Section 7.2 contains more information about following in the track of an icebreaker.

3.4.10 Ice Chart Symbols - Chart Scale

While reading a Daily Ice Analysis Chart or a Weekly Regional Ice Chart produced by the Canadian Ice Service, a mariner will never encounter the following notations: Snow cover, Ridging, Compacting, Pressure, Cracks, Leads, Shear lines, Puddling, or possibly Stages of melting (See 3.4.1). The reason for this lack of information on ice charts is linked to the physical size of the ice charts and the ability to place data on a chart and still make it legible after being transmitted by radio facsimile. The air reconnaissance aircraft, Can Ice 3 is permitted more latitude, due to its tactical nature. The 1:1,000,000 chart scale used to report the ice and visual observations allow the crew to use the full range of the MANICE symbols.

Mariners should know that the Canadian Ice Service of Environment Canada now has the ability to tailor Ice Analysis Charts to an individual ship’s operational area or geographic region in varying degrees of detail. An array of possibilities exist now that Radarsat is in full operation. For more information refer to Section 4.5.

3.5 Examples: Ice Regimes and their Ice Numeral Calculations

In this User Assistance Package two slightly Ice Multiplier Tables are provided to permit the calculation of Ice Numerals. The version on page 11 provides explanatory notes that link the Ice Codes to the Ice Types. The second table is the plasticized version that is larger in scale and designed to be left on the chart table. Either of these tables allows the user to look at an ice egg and quickly calculate Ice Numerals.

The following examples are of realistic Ice Numeral calculations based on ice “eggs” from Daily Ice Analysis Charts or in the case of Example 4, a Tactical Ice Reconnaissance Chart. For each case, two different ships were used to illustrate how the Ice Numerals fluctuate for the same ice with structurally different vessels.

Example 1

Ice Egg
This mid-summer’s Ice Regime consists of 8/10th’s total ice concentration of
1 7
which: 1/10th is Old ice and 7/10th’s Thick First-Year ice. While doing the
7 4•
calculation remember to incorporate the 2/10th’s of Open Water.
4 3
Ice Numeral calculations: Type A ship: (1 x -4) + (7 x -1) + (2 x 2 for open water) = -7 [A Negative Regime] CAC 4 ship: (1 x -4) + (7 x +1) + (2 x 2 for open water) = +7 [A Positive Regime] or If this regime happened to be Ridged: With Ridged thick first-year ice the Ice Numeral calculations are:
Type A ship: (1 x -4) + (7 x -2) + (2 x 2 for open water) = -14 [A Negative Regime] CAC 4 ship: (1 x -4) + (7 x 0) + (2 x 2 for open water) = 0 [A Positive Regime]

Example 2

Ice Egg
This July 9th Ice Regime consists of 6/10th’s total concentration of ice of which:
1 4 1
1/10th is Old ice, 4/10th’s is Thick First-Year and 1/10th of Medium First-Year ice.
7 4 1•
6 3 3
Ice Numeral Calculations: Type E ship: (1 x -4) + (4 x -3) + (1 x -2) + (4 x +2 for open water) = -10 [A ‘Negative’ Regime] Type A ship: (1 x -4) + (4 x -1) + (1 x +1) + (4 x +2 for open water) = +1 [A ‘Positive’ Regime] or If this regime happened to be Decayed based upon data on an ice chart:
With Decayed ice (all Ice Types) the Ice Numeral calculations are: Type E ship: (1 x -3) + (4 x -2) + (1 x -1) + (4 x +2 for open water) = -4 [A Negative Regime] Type A ship: (1 x -3) + (4 x 0) + (1 x +2) + (4 x +2 for open water) = +7 [A Positive Regime]

Example 3

Ice Egg
This Nov. 11th Ice Regime consists of 9/10th’s plus total concentration1 of ice in which:
7 3
there is a trace of Multi-Year ice, 7/10th’s Thin First-Year and 3/10th’s of Grey-White ice.
9• 7 5
(Note: A trace of Multi-Year or Old ice creates a high risk transit.)
6 5
Ice Numeral Calculations: CAC 4 ship: (7 x 2) + (3 x 2) = +20 [A Positive Regime] (Traces of ice are not factored in Type C ship: (7 x -1) + (3 x 1) = -4 [A Negative Regime] the calculation, i.e. under 1/10th)

Example 4

Ice Egg
This data that has been interpreted from remote sensing imagery (Radar / NOAA etc.)
3 4 3
indicates that this regime of 9/10th’s plus1 ice, consists of: 3/10th’s Old ice, 4/10th’s
7• 6 3
of First-Year (considered thick) and 3/10th’s of Young ice (considered Grey-White).
5 4 X
Ice Numeral calculations: Type B ship: (3 x -4) + (4 x -2) + (3 x +1) = -17 [A Negative Regime] CAC 3 ship: (3 x -1) + (4 x +2) + (3 x +2) = +11 [A Positive Regime] 1. “Total ice concentrations of 9/10th’s plus (9+) are considered 10/10th’s for the purposes of Ice Numeral calculations”. (ASPPR Ice Regime Project - Case Studies of the IN Concept, TP 8890 page 5)

1. Page 2 of Arctic Ice Regime Shipping System (AIRSS) Standards, June 1996, TP12259

2. Experience With The Proposed Ice Regime Shipping Control System, Oct. 90, TP 10612

3. Proposed CASPPR 1990 Ice Regime Shipping Control System Seminar / Workshop, June 90

4. Implementation Meeting On The Ice Regime System - Summary Minutes, September 94

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