Section 1 Standard load scenarios

1.1 General

1.1.1 This Section provides further background on the standard load scenarios used for developing requirements for Stern First Ice Class Ships.

1.2 Hull standard load scenarios

1.2.1 The hull standard load scenarios have been developed from considering the ice conditions and operational mode combinations for likely operating conditions for Stern First Ice Class Ships.

1.2.2 A combination case of crossing ridges and turning in ice is considered to be the standard load scenario for developing loads and identifying load areas. Crossing of ridges going stern first gives rise to additional loads at the stern due to the structure meeting unbroken ice when going stern first.

1.2.3 Turning in ice using the enhanced directional thrust of the propulsion unit gives rise to additional loads along the ice belt, at the aft shoulder (flat of side) and forward of the flat of side.

1.2.4 For the combination case, the ice condition considered to give the highest load on the hull is contact with the consolidated layer in a ridge, or at the edge of an old ice channel.

1.2.5 Supporting illustrations for the scenarios described are given in Table 2.1.3 Hull scenarios.

1.2.6 Additional strengthening areas indicated in the Rules have been derived from the reasoning given in Table 2.1.1 Reasoning of hull area distribution for hull standard load scenario.

1.2.7 Assumed speeds for operating stern first in ice, considered by the standard load scenarios, are indicated in Table 2.1.2 Assumed speeds for operating stern first in ice. The assumed speed is related to the achievable open water speed Vow.

1.2.8 Typical hull loading locations associated with the Table 2.1.3 Hull scenarios are conceptually shown in Figure 2.1.1 Example hull loading areas.

Table 2.1.1 Reasoning of hull area distribution for hull standard load scenario

Area	Operational Scenario Consideration
Existing ice belt	Going stern first the ship will experience ice impacts in the stern ice belt region as though the stern were a bow of a conventional ice class vessel
Below the lower ice waterline	The skeg will not be entirely protected by the flushing effects of the podded propulsion unit. Additionally, ice pieces may travel forward below the ice belt. This also accounts for the increased potential of lateral movement afforded to directional propulsion unit equipped ships
Propulsion unit strut	The strut will experience ice loads due to contact with level ice consolidated layer (see propulsion unit scenarios)
Forward of aft flat of side	Owing to the shallower flat of side angle for most large Stern First Ice Class Ships, the shoulder region forward of the flat of side will experience some additional ice load when turning and manoeuvring. This also accounts for the increased potential of lateral movement afforded to directional propulsion unit equipped ships

Table 2.1.2 Assumed speeds for operating stern first in ice

Operational scenario	Level ice	Broken lead		Ridges
Operational scenario	Level ice	New	Old	Ridges
Stern First (straight ahead)	0,7Vow	0,75Vow	0,6Vow	Not applicable
Stern First (oblique to ice)	0,7Vow	0,75Vow	0,6Vow	Not applicable
Stern First (continuous turning)	<<Vow	0,7Vow	0,4Vow	Not applicable
Stern First into ridges	Not relevant	Not relevant	Not relevant	0,3Vow

Table 2.1.3 Hull scenarios

Orientation	Description
	The vessel proceeds through the ice stern first with a constant speed
	The vessel proceeds at an angle through the ice stern first with a constant speed
	The vessel proceeds through the ice stern first with a constant rate of turn

Figure 2.1.1 Example hull loading areas

1.3 Propulsion unit standard operational scenario

1.3.1 Details of the consolidated ridge combination scenario that forms the basis of the propulsion unit standard load scenario are given in Figure 2.1.2 Consolidated ridge combination scenario. Figure 2.1.2 Consolidated ridge combination scenario illustrates the combination of the keel consolidated layer impacting on the strut and the propeller collecting the load from the unconsolidated keel. These are the standard load scenarios for the propulsion unit. Supporting illustrations for other scenarios considered during the development of the standard load scenarios are given in Table 2.1.4 Propulsion unit scenarios.

Figure 2.1.2 Consolidated ridge combination scenario

1.3.2 For the propeller and propulsion shafting the standard load scenario is associated with a blade break on a thick ice sheet. See Figure 2.1.3 Blade break scenario. This standard load scenario may be adopted for initial dimensioning purposes for the propeller and propulsion shafting. In addition, it is a requirement that the relevant requirements of the PC Rules and FS Rules be met with regards to propulsion shafting. These Rules assume an ice block impact scenario.

Figure 2.1.3 Blade break scenario

1.3.3 Figure 2.1.2 Consolidated ridge combination scenario and Figure 2.1.3 Blade break scenario have been combined in the Rules.

Table 2.1.4 Propulsion unit scenarios

Scenario	Prevailing ice conditions	Load area Items in () indicate non-significant load
		Propulsion unit	Propeller
	Broken channel Ridges/rubble field	(Upper strut)	Blade tip
Ice block-propeller impact
	Ridges/rubble field	(Upper strut)	Propeller hub
Ice block – crushing at propulsion unit level
	Ice floes Thick level ice	Upper strut	Blade tip
Ice milling (floe)
	Ice floes Thick level ice	Lower strut	(Blade tip)
Ice crushing at strut
	Ridges/rubble field	(Strut)	Entire blade
Stopped propeller in ridge keel
	Ridges/rubble field Broken channels	(Strut)	Propeller hub
Ice crushed against propeller
	Floes Thick level ice	(Strut)	Upper blade tip
Blade breaking on thick ice sheet
	Ice massive Ground	(Strut)	Lower blade tip (May be taken as similar loading to upper blade tip)
	Ridges/rubble fields	Upper strut	Entire blade
Consolidated ridge combination