Section 3 Machinery Requirements for Polar Class Ships

301. Application

The contents of this Section apply to main propulsion, steering gear, emergency and essential auxil- iary systems essential for the safety of the ship and the survivability of the crew.

302.

Drawings & particulars to be submitted and system design

1. Drawings & particulars to be submitted

(1) Details of the environmental conditions and the required ice class for the machinery, if different from ship's ice class.

(2) Detailed drawings of the main propulsion machinery. Description of the main propulsion, steer- ing, emergency and essential auxiliaries are to include operational limitations. Information on es-

sential main propulsion load control functions.

(3) Description detailing how main, emergency and auxiliary systems are located and protected to prevent problems from freezing, ice and snow and evidence of their capability to operate in in-

tended environmental conditions.

(4) Calculations and documentation indicating compliance with the requirements of this Section.

2. System design

(1) Machinery and supporting auxiliary systems shall be designed, constructed and maintained to comply with the requirements of "periodically unmanned machinery spaces" with respect to fire safety. Any automation plant (i.e. control, alarm, safety and indication systems) for essential sys- tems installed is to be maintained to the same standard.

(2) Systems, subject to damage by freezing, shall be drainable.

(3) Single screw ships classed PC1 to PC5 inclusive shall have means provided to ensure sufficient vessel operation in the case of propeller damage including CP-mechanism.

303. Materials

1. Materials exposed to sea water

Materials exposed to sea water, such as propeller blades, propeller hub and blade bolts shall have an elongation not less than 15% on a test piece the length of which is five times the diameter.

Charpy V impact test shall be carried out for other than bronze and austenitic steel materials. Test pieces taken from the propeller castings shall be representative of the thickest section of the blade. An average impact energy value of 20 J taken from three Charpy V tests is to be obtained at

minus 10℃.

2.

3.

304.

Materials exposed to sea water temperature

Materials exposed to sea water temperature shall be of steel or other approved ductile material. An average impact energy value of 20 J taken from three tests is to be obtained at minus 10℃.

Material exposed to low air temperature

Materials of essential components exposed to low air temperature shall be of steel or other approved ductile material.

An average impact energy value of 20 J taken from three Charpy V tests is to be obtained at 10℃

below the lowest design temperature.

Ice interaction load

1. Propeller ice interaction

These Rules cover open and ducted type propellers situated at the stern of a vessel having control- lable pitch or fixed pitch blades. Ice loads on bow propellers and pulling type propellers shall receive special consideration. The given loads are expected, single occurrence, maximum values for the whole ships service life for normal operational conditions. These loads do not cover off-design operational conditions, for example when a stopped propeller is dragged through ice. These Rules apply also for azimuth(geared and podded) thrusters considering loads due to propeller ice interaction. However, ice loads due to ice impacts on the body of azimuth thrusters have to be es- timated with suitable methods, but ice load formulae are not available in this Section.

The loads given in section 304. are total loads (unless otherwise stated) during ice interaction and are to be applied separately (unless otherwise stated) and are intended for component strength cal- culations only. The different loads given here are to be applied separately.

is a force bending a propeller blade backwards when the propeller mills an ice block while rotating ahead.

is a force bending a propeller blade forwards when a propeller interacts with an ice block while rotating ahead.

2. Ice class factors

The Table below lists the design ice thickness and ice strength index to be used for estimation of the propeller ice loads.

Table 2.10 Ice class factors

3. Design ice loads for open propeller

(1) Maximum backward blade force,

when lim, · · ·

· (kN)

when ≥ lim , · · ·

· · (kN)

where

lim ·

is the nominal rotational speed(at MCR free running condition) for CP-propellers and 85% of the nominal rotational speed(at MCR free running condition) for a FP-pro- peller (regardless driving engine type).

is to be applied as a uniform pressure distribution to an area on the back(suction) side of the blade for the following load cases.

(A) Load case 1 : from 0.6 to the tip and from the blade leading edge to a value of 0.2

chord length,

(B) Load case 2 :

(C) Load case 5 :

a load equal to 50 % of the is to be applied on the propeller tip area outside of 0.9 ,

for reversible propellers a load equal to 60% of the , is to be applied from 0.6 to the tip and from the blade trailing edge to a value

of 0.2 chord length.

See load cases 1, 2, and 5 in Table 2.1

(2) Maximum forward blade force,

of Annex 2.

when lim, · ·

when ≥ lim ,

· · ·

· (kN)

where

lim · (m)

= propeller hub diameter (m)

= propeller diameter (m)

= expanded blade area ratio

= number of propeller blades

is to be applied as a uniform pressure distribution to an area on the face(pressure) side of the blade for the following load cases.

(A) Load case 3 : from 0.6 to the tip and from the blade leading edge to a value of 0.2 chord length,

(B) Load case 4 :

(C) Load case 5

a load equal to 50 % of the is to be applied on the propeller tip area outside of 0.9 ,

: for reversible propellers a load equal to 60% of the , is to be applied from 0.6 to the tip and from the blade trailing edge to a value of 0.2 chord length.

See load cases 3, 4, and 5 in Table 2.1 of Annex 2.

(3) Maximum blade spindle torque

Spindle torque around the spindle axis of the blade fitting shall be calculated both for the

load cases described in (1) & (2) for , . If the spindle torque fault value given below, the default minimum value shall be used.

values are less than the de-

Default Value ㆍ ㆍ

where

= the length of the blade chord at 0.7 radius (m)

is either or which ever has the greater absolute value.

(4) Maximum propeller ice torque applied to the propeller

When lim ,

· · ·

max · · ·

(kNm)

When ≥ lim,

·

max · · · · (kNm)

where

lim

= Ice strength index for blade ice torque

= propeller pitch at 0.7 (m)

= max thickness at 0.7 radius

is the rotational propeller speed, [rps], at bollard condition. If not known, n is to be taken as follows:

Table 2.11 The rotational propeller speed at bollard condition value

Where is the nominal rotational speed at MCR, free running condition.

For CP propellers, propeller pitch, shall correspond to MCR in bollard condition. If not

known, is to be taken as · , is propeller pitch at MCR free running condition.

(5) Maximum propeller ice thrust applied to the shaft

(kN)

(kN)

4. Design ice loads for ducted propeller

(1) Maximum Backward Blade Force,

when

lim

, · · ·

· (kN)

when ≥ lim, · · ·

· (kN)

where

lim ·

is to be taken as in 304. 3 (1)

is to be applied as a uniform pressure distribution to an area on the back side for the lowing load cases(See Table 2.2 of Annex 2) :

(A) Load case 1 : On the back of the blade from 0.6 to the tip and from the blade edge to a value of 0.2 chord length,

fol- leading

(B) Load case 5 : for reversible rotation propellers a load equal to 60% of the is

applied on the blade face from 0.6 to the tip and from the blade trailing edge to a value of 0.2 chord length,

(2) Maximum forward blade force,

when ≤ lim,

when lim ,

· · (kN)

· · ·

(kN)

where

lim

· (m)

is to be applied as a uniform pressure distribution to an area on the face (pressure) side for the following load case (see Table 2.2 of Annex 2) :

(A) Load case 3 : On the blade face from 0.6 to the tip and from the blade leading edge to a value of 0.5 chord length

(B) Load case 5 : a load equal to 60% is to be applied from 0.6 to the tip and from

the blade leading edge to a value of 0.2

(3) Maximum propeller ice torque applied to the propeller

chord length.

max

is the maximum torque on the propeller due to ice-propeller interaction.

When ≤ lim,

· ·

max ·

· · · (kNm)

When lim ,

max · ·

· · · ·

(kNm)

where

lim · (m)

is the rotational propeller speed [rps] at bollard condition. If not taken as follows:

known, n is to be

Table 2.12 The rotational propeller speed at bollard condition value

Where is the nominal rotational speed at MCR, free running condition.

For CP propellers, propeller pitch, shall correspond to MCR in bollard condition. If not

known, is to be taken as · , is propeller pitch at MCR free running condition.

(4) Maximum blade spindle torque for CP-mechanism design,

Spindle torque around the spindle axis of the blade fitting shall be calculated for the load

case described in 304. 1. If the spindle torque values are less than the default value given be- low, the default value shall be used.

Default Value (kNm)

where

= the length of the blade section at 0.7R radius (m)

is either or which ever has the greater absolute value.

(5) Maximum propeller ice thrust (applied to the shaft at the location of the propeller)

·

5. Design loads on propulsion line

(1) Torque

The propeller ice torque excitation for shaft line dynamic analysis shall be described by a sequence of blade impacts which are of half sine shape and occur at the blade. The torque due

to a single blade ice impact as a function of the propeller rotation angle is then

· max·

when

when

where and parameters are given in table below.

Table 2.13 and parameters

The total ice torque is obtained by summing the torque of single blades taking into account the phase shift 360 deg./Z. The number of propeller revolutions during a milling sequence shall be obtained with the formula :

·

The number of impacts is ·

See Fig 2.1 of Annex 2.

Milling torque sequence duration is not valid for pulling bow propellers, which are subject to special consideration. The response torque at any shaft component shall be analysed considering excitation torque at the propeller, actual engine torque, , and mass elastic system

= actual maximum engine torque at considered speed

Design torque along propeller shaft line

The design torque ( ) of the shaft component shall be determined by means of torsional vibration analysis of the propulsion line. Calculations have to be carried out for all excitation cases given above and the response has to be applied on top of the mean hydrodynamic torque in bollard condition at considered propeller rotational speed.

(2) Maximum response thrust

Maximum thrust along the propeller shaft line is to be calculated with the formula below. The factors 2.2 and 1.5 take into account the dynamic magnification due to axial vibration. Alternatively the propeller thrust magnification factor may be calculated by dynamic analysis.

Maximum Shaft Thrust Forwards · (kN) Maximum Shaft Thrust Backwards · (kN)

= propeller bollard thrust (kN)

= maximum forward propeller ice thrust (kN)

If hydrodynamic bollard thrust, is not known, is to be taken as follows:

Table 2.14 Propeller bollard thrust

= nominal propeller thrust at MCR at free running open water conditions

(3) Blade failure load for both open and nozzle propeller

The force is acting at 0.8 in the weakest direction of the blade and at a spindle arm of 2/3 of the distance of axis of blade rotation of leading and trailing edge which ever is the greatest. The blade failure load is:

ㆍ ㆍ

ㆍ ㆍ (kN)

where

·

where and are representative values for the blade material.

, and (see Fig 1.7) are respectively the actual chord length, thickness and radius of

the cylindrical root section of the blade at the weakest section outside root fillet. And typi-

305.

Design

1. Design principle

The strength of the propulsion line shall be designed for maximum loads in 304. such that the plastic bending of a propeller blade shall not cause damages in other propulsion line components with sufficient fatigue strength.

2. Azimuth main propulsors

In addition to the above requirements special consideration shall be given to the loading cases which are extraordinary for propulsion units when compared with conventional propellers. Estimation of the loading cases must reflect the operational realities of the ship and the thrusters. In this respect, for example, the loads caused by impacts of ice blocks on the propeller hub of a pulling propeller must be considered. Also loads due to thrusters operating in an oblique angle to the flow must be considered. The steering mechanism, the fitting of the unit and the body of the thruster shall be designed to withstand the loss of a blade without damage. The plastic bending of a blade shall be considered in the propeller blade position, which causes the maximum load on the studied component.

Azimuth thrusters shall also be designed for estimated loads due to thruster body/ice interaction as per Sec.2 211.

3. Blade design

(1) Maximum blade stresses

Blade stresses are to be calculated using the backward and forward loads given in section 304.

3 & other

4. The stresses shall be calculated with recognised and well documented FE-analysis or acceptable alternative method. The stresses on the blade shall not exceed the allowable

stresses for the blade material given below.

Calculated blade stress for maximum ice load shall comply with the following:

is reference stress, defined as:

ㆍ or

ㆍ ㆍ which

Where and are representative values for the blade material.

(2) Blade edge thickness

The blade edge thicknesses and tip thickness are to be greater than given by the following formula:

≥

= distance from the blade edge measured along the cylindrical sections from the edge and shall be 2.5% of chord length, however not to be taken greater than 45 mm.

In the tip area (above 0.975 radius) x shall be taken as 2.5% of 0.975 section length and is to be measured perpendicularly to the edge, however not to be taken greater than 45 mm.

= safety factor

= 2.5 for trailing edges

= 3.5 for leading edges

= 5 for tip

according to 304. 2

= ice pressure

16 MPa for leading edge and tip thickness according above Par. 3 (1)

The requirement for edge thickness has to be applied for leading edge and in case of reversible rotation open propellers also for trailing edge. Tip thickness refers to the maximum measured thickness in the tip area above 0.975 radius. The edge thickness in the area between position of maximum tip thickness and edge thickness at 0.975 radius has to be interpolated between edge and tip thickness value and smoothly distributed.

4. Prime movers

(1) The Main engine is to be capable of being started and running the propeller with the CP in full pitch.

(2) Provisions shall be made for heating arrangements to ensure ready starting of the cold emer- gency power units at an ambient temperature applicable to the polar class of the ship.

(3) Emergency power units should be equipped with starting devices with a stored energy capability of at least three consecutive starts at the design temperature in (2) above. The source of stored

energy shall be protected to preclude critical depletion by the automatic starting system, unless a second independent means of starting is provided. A second source of energy shall be provided for an additional three starts within 30 min., unless manual starting can be demonstrated to be

effective.

306. Machinery fastening loading accelerations

1. Essential equipment and main propulsion machinery supports shall be suitable for as indicated in as follows. Accelerations are to be considered acting independently.

2. Longitudinal impact accelerations,

Maximum longitudinal impact acceleration at any point along the hull girder,

the accelerations

2

△ tan

3. Vertical acceleration,

Combined vertical impact acceleration at any point along the hull girder,

2

△ (m/s )

= 1.3

= 0.2

= 0.4

= 1.3

at FP

at midships at AP

at AP for ships conducting ice breaking astern intermediate values to be interpolated linearly

4. Transverse impact acceleration,

Combined transverse impact acceleration at any point along hull girder,

(m/s2)

= 1.5 at FP

= 0.25 at midships

= 0.5 at AP

= 1.5 at AP for ships conducting ice breaking astern intermediate values to be interpolated linearly

where

: maximum friction angle between steel and ice, normally taken as 10˚ [deg.]

: bow stem angle at waterline [deg.]

△ : displacement

: length between perpendiculars (m)

: distance in meters from the water line to the point being considered (m)

: vertical impact force, defined in 209. 2

: total force normal to shell plating in the bow area due to oblique ice impact,

209. 3

defined in

307.

Auxiliary systems

1. Machinery shall be protected from the harmful effects of ingestion or accumulation of ice or snow.

Where continuous operation is necessary, means should be provided to purge the system of accu- mulated ice or snow.

2. Means should be provided to prevent damage due to freezing, to tanks containing liquids.

3. Vent pipes, intake and discharge pipes and associated systems shall be designed to prevent block- age due to freezing or ice and snow accumulation.

308.

Sea chest and cooling water systems

1. Cooling water systems for machinery that are essential for the propulsion and safety of the vessel, including sea chests inlets, shall be designed for the environmental conditions applicable to the ice class.

2. At least two sea chests are to be arranged as ice boxes for class PC1 to PC5 inclusive where. The calculated volume for each of the ice boxes shall be at least 1 m3 for every 750 kW of the total installed power. For PC6 and PC7 there shall be at least one ice box located preferably near center

line.

3. Ice boxes are to be designed for an effective separation of ice and venting of air.

4. Sea inlet valves are to secured directly to the ice boxes. The valve shall be a full bore type.

5. Ice boxes and sea bays are to have vent pipes and are to have shut off valves connected direct to the shell.

6. Means are to be provided to prevent freezing of sea bays, ice boxes, ship side valves and fittings above the load water line.

7. Efficient means are to be provided to re-circulate cooling seawater to the ice box. Total sectional area of the circulating pipes is not to be less than the area of the cooling water discharge pipe.

8. Detachable gratings or manholes are to be provided for ice boxes. Manholes are to be located above the deepest load line. Access is to be provided to the ice box from above.

9. Openings in ship sides for ice boxes are to be fitted with gratings, or holes or slots in shell plates.

The net area through these openings is to be not less than 5 times the area of the inlet pipe. The diameter of holes and width of slot in shell plating is to be not less than 20 mm. Gratings of the ice boxes are to be provided with a means of clearing. Clearing pipes are to be provided with screw-

down type non return valves.

309.

Ballast tanks

1. Efficient means are to be provided to prevent freezing in fore and after peak tanks and wing tanks located above the water line and where otherwise found necessary.

310.

Ventilation systems

1. The air intakes for machinery and accommodation ventilation are to be located on both sides of the ship.

2. Accommodation and ventilation air intakes shall be provided with means of heating.

3. The temperature of inlet air provided to safe operation of the machinery.

machinery from the air intakes shall be suitable for the

311.

Alternative design

1. As an alternative a comprehensive design lidated by an agreed test programme.

study may be submitted and may be requested to be va-