Section
2 General requirements
2.1 Pod arrangement
2.1.1 In general,
for a ship to be assigned an unrestricted service notation, a minimum
of two podded propulsion units are to be provided where these form
the sole means of propulsion. For vessels where a single podded propulsion
unit is the sole means of propulsion, an evaluation of a detailed
engineering and safety justification will be conducted by LR, see
Pt 5, Ch 9, 2.2 Plans and information to be submitted 2.2.2 This evaluation process will
include the appraisal of a Failure Modes and Effects Analysis (FMEA)
to verify that sufficient levels of redundancy and monitoring are
incorporated in the podded propulsion unit's essential support systems
and operating equipment.
2.2 Plans and information to be submitted
2.2.1 In addition to the plans required by Pt 5, Ch 5 Gearing, Pt 5, Ch 6 Main Propulsion Shafting, Pt 5, Ch 7 Propellers, Pt 5, Ch 8 Shaft Vibration and Alignment, Pt 5, Ch 14 Machinery Piping Systems and Pt 5, Ch 19 Steering Systems, and Pt 6, Ch 1 Control Engineering Systems and Pt 6, Ch 2 Electrical Engineering, the following plans and information are required to be submitted
for appraisal:
-
Description of
the ship’s purpose/capabilities together with the pod’s
intended operational modes in support of these capabilities.
-
Power transmitted
at MCR condition (shaft power and rpm) and other maximum torque conditions,
e.g. bollard pull.
-
Maximum transient
thrust, torque and other forces and moments experienced during all
envisaged operating modes as permitted by the steering and propulsor
drive control systems.
-
Details of the
electric propulsion motor short-circuit torque and motor air gap tolerance.
-
Sectional assembly
in the Z-X plane, see
Figure 9.2.1 Pod co-ordinate system.
-
Specifications
of materials and NDE procedures for components essential for propulsion
and steering operation to include propulsion shaft and slewing ring
bearings, gearing and couplings, see
Pt 5, Ch 9, 3.1 General.
- The declared steering angle limits are to be stated by manufacturer for each podded
propulsion unit;
-
Details of intended manoeuvring capability of the ship in each
operating condition. (To be declared by the shipyard, see also
Pt 5, Ch 9, 5.6 Steering system 5.6.2)
-
Design loads for
both the pod structure and propeller together with podded propulsion
unit design operating modes (see
Pt 5, Ch 9, 2.4 Global loads 2.4.1, Pt 5, Ch 9, 5.3 Propulsion shafting 5.3.7, Pt 5, Ch 9, 5.6 Steering system 5.6.10 and Pt 5, Ch 9, 5.6 Steering system 5.6.11).
-
Supporting data
and direct calculation reports. This is to include, where applicable,
an assessment of anticipated global accelerations acting on the ship's
machinery and equipment which may potentially affect the reliable
operation of the propulsion system for all foreseeable seagoing and
operating conditions. Typically, this may include response to slamming,
extreme ship motions and pod interaction. See also
Pt 5, Ch 9, 1.1 General 1.1.5.
-
Structural component
details including: strut, pod body, bearing supports, bearing end
caps, ship's structure in way of podded propulsion unit integration
and a welding Table showing a key to weld symbols used on the plans
specifying weld size, type, preparation and heat treatment. The information
should include the following:
- Detailed drawings showing the structural arrangement, dimensions
and scantlings.
- Welding and structural details.
- Connections between structural components (bolting).
- Casting's chemical and mechanical properties.
- Forging's chemical and mechanical properties.
- Material grades for plate and sections
-
Nozzle structure,
its support arrangements, together with related calculations for all
permitted operating conditions where the propeller operates in a nozzle
(duct), see
Pt 3, Ch 13, 3 Fixed and steering nozzles.
-
Propeller shaft
bearing mounting and housing arrangement details, see also
Pt 5, Ch 9, 5.3 Propulsion shafting 5.3.6
-
Details of propeller
shaft and steering bearings, where roller bearings are used supporting
calculations are to be submitted, see
Pt 5, Ch 9, 5.3 Propulsion shafting 5.3.7 and Pt 5, Ch 9, 5.6 Steering system 5.6.11.
-
Propeller shaft
seal details.
-
Details of propeller
shaft and pod steering securing/locking and means of aligning the
securing/locking arrangements.
-
Cooling systems
piping system schematic.
-
Details of any
lubricating oil conditioning systems (filtering/cooling/heating) and
control arrangements necessary to ensure the continuous availability
of the required lubricating oil quality to the propeller shaft bearings.
-
Details of installed
condition monitoring equipment.
-
Details of the
derivation of any duty factor used in the design of the steering gears.
-
Identification
of any potentially hazardous atmospheric conditions together with
details of how the hazard will be countered, this should include a
statement of the maximum anticipated air temperature within the pod
during full power steady state operation, see
Pt 5, Ch 9, 2.3 Pod internal atmospheric conditions
-
Where provided,
access and closing arrangements for pod unit inspection and maintenance.
-
Heat balance calculations
for pods having an electric propulsion motor but no active cooling
system, see
Pt 5, Ch 9, 5.7 Ventilation and cooling systems 5.7.4.
-
Details of proposed
testing and trials required by Pt 5, Ch 9, 8 Testing and trials.
-
Details of emergency
steering and pod securing arrangements. See
Pt 5, Ch 9, 5.3 Propulsion shafting 5.3.11.
-
Quality plan for
electronic control systems and electrical actuating systems.
Figure 9.2.1 Pod co-ordinate system
2.2.2 Where an engineering and safety justification report is required,
the following supporting information is to be submitted:
2.3 Pod internal atmospheric conditions
2.3.1 Machinery
and electrical equipment installed within the pod unit are to be suitable
for operation, without degraded performance, at the maximum anticipated
air temperature and humidity conditions within the pod unit with the
pod operating at its maximum continuous rating in sea water of not
less than 32°C after steady state operating conditions have been
achieved.
2.3.2 Precautions
are to be taken to prevent as far as reasonably practicable the possibility
of danger to personnel and damage to equipment arising from the development
of hazardous atmospheric conditions within the pod unit. Circumstances
that may give rise to these conditions are to be identified and the
counter measures taken are to be defined.
2.4 Global loads
2.4.1 The overall strength of the podded propulsion unit structure is to be based
upon the maximum anticipated in-service loads, including, the effects of ship
manoeuvring and of ship motion (see
Pt 3, Ch 14, 1.7 Symbols and definitions, in Pt 3, Ch 14 Cargo Securing Arrangements). This is to include the effects of any pod to pod and/or
pod to ship hydrodynamic interference effects. The designer is to supply the following
maximum load and moment values to which the unit may be subjected with a description of
the operating conditions at which they occur.
-
F
x, Force in the longitudinal direction;
-
F
y, Force in the transverse direction;
-
F
z, self weight, in water, augmented by
the ship’s pitch and heave motion and flooded volume where applicable, see
Pt 3, Ch 14 Cargo Securing Arrangements;
-
M
x, moment at the slewing ring about the
pod unit’s global longitudinal axis;
-
M
y, moment at the slewing ring about the
pod unit’s global transverse axis;
-
M
z, moment at the slewing ring about the
pod unit’s vertical axis (maximum dynamic duty steering torque
on steerable pods).
The directions of the X, Y and Z axes, with the origin at the
centre of the slewing ring, are shown in Figure 9.2.1 Pod co-ordinate system.
2.4.2 Where
the maximum forces and moments defined in Pt 5, Ch 9, 2.4 Global loads 2.4.1 cannot be accurately calculated,
then, an estimate of these loadings is to be stated together with
an assessment of the associated error tolerances for the sequences
of permitted design manoeuvres, see
Pt 5, Ch 9, 1.1 General 1.1.7. Typically this will include
emergency astern manoeuvres, zig zag manoeuvres and pod interaction.
Such estimates are to be defined on a load versus pod angle basis.
In the case of pod to pod and/or pod to ship hydrodynamic interaction
effects these, must be defined for the most severely affected propulsor.
2.4.3 Where
control systems are installed to limit the operation of the podded
drive to defined angles at defined ship speeds, this information may
be taken into consideration when determining the pod unit loading.
2.4.4 Where
pod units are fixed about their Z axis, then maximum global loads,
to be used as the basis of the structural appraisal, are to be determined
for inflows in 5 degree increments between the extremes of anticipated
inflow angle during manoeuvring with ship at full speed and maximum
propeller thrust.
2.4.5 The
podded propulsor is to be capable of withstanding a blade root failure
due to fatigue occurring at the maximum rated output of the podded
propulsor without initiating a failure in other parts of the propulsor
system.
2.5 Failure Modes and Effects Analysis (FMEA)
2.5.1 An FMEA
is to be carried out where a single podded propulsion unit is the
vessel’s sole means of propulsion, see
Pt 5, Ch 9, 2.1 Pod arrangement 2.1.1. The FMEA is to identify components
where a single failure could cause loss of all propulsion and/or steering
capability and the proposed arrangements for preventing and mitigating
the effects of such a failure. The assessment required by Pt 6, Ch 2, 16.2 System design and arrangement 16.2.2 may be considered
for demonstrating the acceptability of the proposed design for propulsion
power purposes.
2.5.3 The
FMEA is to be organised in terms of equipment and function. The effects
of item failures at a stated level and at higher levels are to be
analysed to determine the effects on the system as a whole. Actions
for mitigation of the effects of failure are to be determined, see
Pt 5, Ch 9, 2.5 Failure Modes and Effects Analysis (FMEA) 2.5.1.
2.5.4 The
FMEA is to:
-
identify the equipment
or sub-system and mode of operation;
-
identify potential
failure modes and their causes;
-
evaluate the effects
on the system of each failure mode;
-
identify measures
for reducing the risks associated with each failure mode;
-
identify measures
for preventing failure; and
-
identify trials
and testing necessary to prove conclusions.
2.5.5 At sub-system
level it is acceptable, for the purpose of these Rules, to consider
failure of equipment items and their functions, e.g. failure of a
pump to produce flow or pressure head. It is not required that the
failure of components within that pump be analysed. In addition, their
failure need only be dealt with as a cause of failure of the pump.
2.5.6 Where
FMEA is used for consideration of systems that depend on software-based
functions for control or coordination, the analysis is to investigate
failure of the functions rather than a specific analysis of the software
code itself.
2.6 Ice Class requirements
2.7 Condition Monitoring
2.7.1 Where Thruster Condition Monitoring (ThCM) ShipRight descriptive note has been
requested, refer to ShipRight Procedure Machinery Planned Maintenance and
Condition Monitoring, Section 8.
|