SMART COMBINATORS

SMART COMBINATORS

HZ University of Applied Sciences ‘De Ruyter Academy’, Vlissingen

Appendix 1: Literature Study

Course: CU05994 Date: 5 June 2014 Version: 2.0 1

SMART COMBINATORS

Appendix 1: Literature Study


1.1 Introduction

The literature study will be done to understand the combinator background and its

operating principles. These operating principles are vital to understand before one

can make a Combinator. To help make this case on how a combinator operates

some questions can be made to guide the process of the literature study.

What makes the ship move?

What is the function of a CPP?

How is the pitch regulated?

What is the purpose of a gearbox?

What is a combinator?

What types of engine and pitch control are available?

Where is a combinator of use?

What is the purpose of a combinator?

What is the engine power envelope?

What parameters influence the design of a combinator?

How can a combinatory diagram be designed?

Advantages and disadvantages of a combinator?

How is the ship affected by different conditions?

How is the propeller affected by different conditions?

What are Sea Margin and Engine Margin?

What parameters influence the operation point of a combinator?

What is the effect of propeller design conditions on the layout of the

combinator?

How is the dynamic response of the combinator of the complete power train?

How does the combinatory interact with the control system parts such as load

control and fuel rack?

How is the combinator curve affected by different drive train configurations?

Are there general guidance rules on the combinatory layout?

What are Ice Class Requirements?

Verification and validation

What makes the ship move?

The ship is propelled by means of a propeller; other propulsor types are out of scope

of this research. The propeller creates Thrust in the ships heading in order to

overcome the frictional resistance (Figure 1: Thrust and Resistance). The Resistance

will increase with speed and therefore the thrust becomes equal to the resistance at

a certain speed. The propeller inputs are torque and rotational speed. The outputs

are thrust and speed (and several losses).


Figure 1: Thrust and Resistance

Thrust

‘The propulsor converts the rotating mechanical power delivered by the engine into

translating mechanical power to propel the ship. The engine power is torque M times

an angular velocity ω: Pb=Mb*ωe’ (Klein Woud & Stapersma, 2008). It is converted

into the thrust force T at ship’s velocity Vs: Pt=T*Vs. The propeller can be seen by

means of the axial disc theory (Figure 2: Axial disc theory) T=A*Δp, A is the disc area

and Δp the pressure jump in the propeller disc. The increase of water pressure in the

disc area results that the water speed after the propeller will increase due to the

induced velocity. Bernoulli’s law: P+1/2*ρ*V2=Constant implies that the pressure in

the propeller disc is build up, and after the propeller disc the pressure will return to

original condition, resulting in an increase of water speed.

Figure 2: Axial disc theory

Torque

Torque can be defined mathematically as: the cross product of the lever-arm

distance and force. The torque is a measure for the force needed to rotate the

propeller at a certain speed. The propeller torque can be altered by means of adding

a gearbox Me/i=Ms. Changing the gear ratio ‘i’ to less than one will multiply the torque

by the same factor. However this implies that the rotational speed of the propeller

shaft will decrease with the same factor.


What is the function of a CPP?

The function of a Controllable Pitch Propeller (CPP) and a Fixed Pitch Propeller

(FPP) is to propel the ship. Distinctive of a CPP is the ability to change propeller pitch

or ‘angle of attack’ to the water, giving the advantage of optimising the engine load in

adverse weather and manoeuvring conditions. A disadvantage of the CPP is the

additional components and systems, leading to an increased risk of failure. Also due

to the components in the propeller hub the diameter is increased resulting in an

efficiency loss compared to the FPP. The main reason to choose a CPP is to improve

manoeuvrability, since the pitch can be set to ‘zero’ or set to ‘astern’ while the

propulsor is still running. Note that during zero pitch still approximately 20% of engine

power is consumed by the propeller due to the frictional losses. Also unfavourable

blade loading could occur during zero pitch, some part of the blade creates positive

thrust while the other side creates negative thrust. Below different pitch settings are

shown in ‘Figure 3: Pitch settings.

Figure 3: Pitch settings

The CPP also enables to reduce load on the engine, this is realised by reducing the

pitch. This prevents the engine from overloading in adverse conditions or during

extreme acceleration or crash stop situations. Below (Figure 4: Open water curve

and power absorption diagram at full load and Figure 5: Open water curve and power

absorption diagram at low load) are power absorption diagrams shown of a

controllable pitch propeller, in these diagrams the combinator curve, propeller curve


and power envelope are displayed as well as the propeller open water curve.

Figure 4: Open water curve and power absorption diagram at full load

Figure 5: Open water curve and power absorption diagram at low load

How is the pitch regulated?

The CPP is operated by a hydraulic system. This system involves pumps, actuators,

valves and controllers. To change the pitch hydraulic oil is pumped into the forward

or aft cylinder compartment, the yoke moves due to the sliding action of the cylinder

(Figure 6: CPP drawing of components). The yoke is connected to the blade carrier

by means of a crank pin, which in turn will turn the blade. One can imagine that the

speed of pitch change depends on the size of the cylinder and the flow of hydraulic

oil, this is dictated by the propeller and hub size.


Courtesy of Wärtsilä

Figure 6: CPP drawing of components

What is the purpose of a gearbox?

The gearbox is the coupling between the engine and propeller, the gearbox is

normally only necessary for four-stroke engines, since two-stroke engines are

operated with such low rpm that the propeller can be coupled directly to the engine.

The purpose of a gearbox is thus to reduce the propeller rpm. As a result of the lower

propeller rpm a larger diameter propeller can be installed. The drawback of a

gearbox is the transmission losses, which exist of frictional, heat and churning

losses.

What is a combinator?

A Combinator is a system for a ship designed with Controllable Pitch Propeller (CPP)

and engine tuned for variable RPM operation. The combinator makes it possible to

operate at a certain engine RPM with a certain pitch, to optimise the drive train

efficiency. The combinator is basically a combinatory diagram which tells the engine

to operate certain RPM and the CPP at the associated pitch at a given lever demand.

The combinatory diagram is made during the design stage of the vessel and is tested

during sea trial.

What types of engine and pitch control are available?

As mentioned above a combinator system is available, a different operating mode

which is commonly used is the constant RPM system. This system as the name

already tells, uses constant engine RPM and varies pitch according to the lever


demand. In this case the pitch changes linear with the change of lever demand see

‘Figure 7: Combinator diagram 'constant RPM'’. This system is often used when a

shaft generator is attached to the drive train.

Figure 7: Combinator diagram 'constant RPM'

Figure 8: Combinator diagram 'variable RPM'

In these figures vertically are the engine power, engine RPM and pitch angle shown. Horizontally the lever demand is shown. Yellow: engine output at free sailing Pink: engine output at bollard condition Red: engine RPM Orange: pitch angle


Where is a combinator of use?

A combinator is of use if the mission profile requires a lot of manoeuvring or sailing at

reduced speeds, the engine output at lower lever demand is significantly less

compared to the constant RPM version see ‘Figure 8: Combinator diagram 'variable

RPM'. The lower engine output is due to less frictional resistance of the water. In this

case the pitch at a certain handle position is higher, resulting in a higher propeller

efficiency and better engine loading. The advantage of this is that the propeller will be

at maximum efficiency as quickly as possible.

What is the purpose of a combinator?

The purpose of a Combinator is to match the propeller pitch as efficiently as possible

to the engine power envelope. The main reason is to reduce specific fuel

consumption at lower ship speeds without overloading the engine. Also the propeller

thrust can be optimised to the telegraph, in some cases it might be useful to create a

linear relationship between the propeller thrust and the ships telegraph.

What is the engine power envelope?

The engine power envelope is a graph that indicates the engine power range see

‘Figure 9: Power envelope’. The graph shows the engine operating area and load

limits, two types of load limits exist; thermal overloading and mechanical overloading.

Figure 9: Power envelope

-Thermal overloading

Thermal overloading occurs due to turbo charging an engine. A turbo charger is an

exhaust gas driven turbine, connected to a compressor. To supply the compressor of

power the turbine needs sufficient exhaust gas flow. If there is insufficient gas flow


through the turbine the compressor is not able to compress air in to the scavenging

air manifold. Resulting in a so called ‘asthmatic engine’, if the engine lacks air the

combustion process will suffer, resulting in lower power output. Also the scavenging

of the cylinder is done insufficient, leaving hot gasses behind and is inadequate for

cooling the cylinder liner, piston crown and exhaust valves. This is results in high

temperatures throughout the engine as well as fouling (Maanen, 2000).

-Mechanical overloading

Mechanical overloading can occur when maximum power (100% fuel rack) is given at

low RPM’s, resulting in high combustion pressures and high loading on bearings and

moving parts (depending on type of engine). This might increase wear behaviour of

the engine.

In the power envelope the mechanical overload line is above the thermal overload

line, meaning that normally mechanical overloading will not occur. Other important

aspects of the power envelope are maximum power and maximum RPM, Maximum

Continues Rating (MCR) is at the intersection of maximum power and RPM. MCR is

as the name already tells is the maximum allowable power the engine can deliver.

Below that (normally 85-90% of MCR and RPM) is the Continues Service Rating

(CSR) this operation area is at which the engine reaches its highest efficiency.

The power envelope can be optimised for special needs, for instance the mission

profile might suggest the best engine operating range for the ships operating

conditions. Changing of the engine operating range is done by means of ‘tuning’ the

engine, at Wärtsilä three types of engine tuning are available; Standard tuning, Delta

tuning and Low Load tuning. The main difference between these types of engine

management is the specific fuel consumption at certain operating ranges. The

Standard tuning has the best fuel efficiency at high engine loads (90+% MCR)

however the efficiency is compromised at load loads. The Delta tuning is most

efficient at medium load ranges (75 – 90% MCR), the Low load tuning is most

efficient for slow steaming or equal conditions (0 – 75% MCR).

What parameters influence the design of a combinator?

Since the combinator is attached to many systems there are many influential factors,

they can be divided in two categories: static and dynamic. Both categories are

influential in the design stage. In addition to the afore mentioned factors a third factor

can be made; Special factors, this may not be considered as highly influential during

the design stage, however they should be taken into account.

-static factors

Static factors are influenced during the design of a vessel, in this stage many

decisions need to be made. The decision made during this stage will have the most

influence on the design of the combinator. The main influential factors are:

Engine type, size and tuning


Gearbox (if applicable)

Propeller diameter and blades

Class bureau (Sea margin)

Engine margin

PTO and PTI

Power envelope (dependant on engine type and size)

-dynamic factors

Dynamic factors are more fine tuned factors and therefore they do not dictate the

combinator design, however they do have a major role in final combinator curve. The

influential dynamic factors are:

Sea margin

Area of trade (mission profile)

Draft of the vessel (related to Engine margin)

Slow steaming application

Towing capabilities

Operating in off design conditions

-Special factors

Special factors are factors which are normally not desirable, however they could

occur and therefore taken into account.

Behaviour in heavy seas

Emergency operation such as crash stop

Blackout operation

Finally there are some restrictions related to the engine operational area which affect

the design of a combinator. Most engines have a critical operating area; in this area

the critical RPM is reached. The critical RPM is when the engine unbalance reaches

the point at which no counter balancing force is present, resulting in resonance and

high torsion vibration. This form of mechanical overloading is engine specific and is

especially a problem for two-stroke engines due to the low engine frequency (Jenzer,

1996). During the design of a combinator it is very important to make sure that the

engine is not operated for a prolonged time in the critical operating area.

How can a combinatory diagram be designed?

The combinatory diagram is designed after the static factors (see above), and the

ships particulars are known. With this information the propeller curve can be made

and the optimum propeller efficiency can be calculated. The propeller curves

(different pitch ratios) can be drawn into the engine power envelope, together with

specific fuel consumption of the engine and constant speed lines. The constraints

need to be taken into account and this result in optimum steps for the combinator to

change pitch and RPM, and benefits efficiency of the overall power train.


Advantages and disadvantages of a combinator?

The advantage of a combinator is the possibility to optimise the propeller pitch to the

engine power envelope, resulting in less fouling of the engine, better propeller

efficiency and optimised drive train efficiency, which in turn will save fuel. A

disadvantage of the combinator system the development of the combinator curve,

this is a time consuming affair. Also if the vessel is sailing at full sea ahead there is

no difference between constant RPM and combinator mode as long as the drive train

is the same (see ‘Figure 7: Combinator diagram 'constant RPM'’ and ‘Figure 8:

Combinator diagram 'variable RPM'’).finally the most important disadvantage is the

inability to continuously operate a shaft generator due to the inconstant RPM.

How is the ship affected by different conditions?

Hull design is out of scope in this research though the basic principles of the ships

influences are necessary to know. The ship has many influencing factors that start

with the design stage, for instance the hull shape, length, beam, draft and block

coefficient are key to the ships resistance curve. During the operational life it is

affected by several frequently changing variables: the sea state, water depth, draft

due to loading of cargo, trim, current, air resistance, hull and propeller fouling. Also

some (almost) consistent factors: water density and water friction. The depth below

the keel is a very important one which will interact with the ships boundary layer. The

ships boundary layer is the area around the ship where the water is slowed down,

due to the friction of the vessel through the water when sailing. The speed at which

the water flows in the boundary layer is the Velocity of Advance (Va). And is the

resultant of the ships speed (Vs) * (1-w). In this formula w is the wake factor. The

wake factor is the ratio between ships speed and advance velocity through the water.

How is the propeller affected by different conditions?

Since the propeller is a crucial part of this research it is important to understand the

propeller behaviour under different circumstances. First the basics of the propeller

need to be addressed. The propeller is driven by the propeller shaft; the propeller

shaft in itself has losses, frictional losses of the thrust bearing and rotational losses in

the shaft bearings (also a type of frictional loss). The shaft seal is included in the total

rotational losses ƞshaft. There are several types of propellers nevertheless the scope

of this research is limited to CPP. Within the CPP propeller are several losses:

Torque delivered to the propeller;

Thrust;

Rotational speed of the propeller;

Propeller diameter;

Velocity of advance;

Pitch reduction;


Those losses combined are called the open water efficiency ƞo. Also there is the

thrust deduction factor, ‘only a part of the thrust produced by the propellers is used to

overcome the pure towing resistance of the ship, the remaining part has to overcome

the added resistance’ (Klein Woud & Stapersma, 2008). This is due to the fact that

the propeller itself is dragging through the water and therefore creating resistance

just like the ship’s hull. The final resistance comes from the surface roughness of the

propeller; this is not taken into account because in design conditions it is within the

open water efficiency, during the lifetime of the propeller the roughness will increase.

When the CPP changes pitch the biggest loss will occur, the open water efficiency

will drop significantly and therefore every CPP has several open water efficiency

lines for different pitch ratio. Reducing the pitch means changing the angle of attack

to the incoming water, which reduces thrust (see ‘Figure 10: open water diagram

100% and 70% pitch’.

(Klein Woud & Stapersma, 2008)

Figure 10: open water diagram 100% and 70% pitch

The propeller also is influenced by external forces. The forces are due to the wake

field created by the ship, the depth of the water and the waves. ‘The boundary layer

at the ships stern has a considerable thickness and normally the propeller is

completely within the region where the water velocity is affected by the hull’s

presence’ (Klein Woud & Stapersma, 2008). Therefore the propeller can create more

thrust from the relatively slow moving water, even though the water speed at the

propeller inlet is considerable higher due to the suction of the propeller.


The water depth is of influence due to the channel effect, ‘Restricted water effects

derive essentially from two sources. These are first a limited amount of water under

the keel and secondly, a limitation in the width of the water each side of the vessel

which may or may not be in association with a depth restriction’ (Molland, 2008). The

influence of water depth is shown in the graph below see ‘Figure 11: influence of

water depth’. In this graph is shown that the water depth and speed of the vessel are

of influence in the propulsion efficiency. Water depth is not part of this research,

nonetheless it does influence propeller behaviour.

(Molland, 2008)

Figure 11: influence of water depth

The water depth also interferes with the cavitation behaviour of the propeller.

‘Cavitation is a general fluid mechanics phenomenon that can occur whenever a

liquid is used in a machine which induces pressure and velocity fluctuations in the

fluid.’ (Carlton, 2007). This implies that the propeller also is susceptible to cavitation

since this induces pressure and velocity fluctuations. The basic physics of cavitation

is when water is depressurised the water will boil at a lower temperature, the boiling

of water creates air bubbles which could implode on the propeller surface as well as

changing the flow over the propeller due to the additional bubble layer. Even though

this is an oversimplified explanation due to for example the ability of fluid to withstand

tensions, it will suffice for this research. The cavitation phenomenon will be taken into

account as a relatively constant factor, implying that only cavitation limits will be part

of the research. Cavitation is a topic to which many studies have been devoted in

the past 100+ years, and still is not fully understood. Currently Computational Fluid

Dynamics (CFD) tools are used to calculate the cavitation behaviour. CFD is mainly

used for preliminary estimation of the propeller behaviour, for better predictions


model tests need to be carried out by means of a cavitation tunnel. This is a costly

affair, and will only be done if the preliminary estimations are promising.

Another external influencing factor on the propeller is waves, the bigger the waves

the more the influencing it will be. Due to waves the vessel starts pitching and the

water pressure on the propeller changes constantly. Normally the water pressure on

the top half of the propeller is already different compared to the bottom half. With the

addition of waves, the water pressure on the propeller changes. Due to the

fluctuating pressure on the propeller additional cavitation may occur. Cavitation can

damage the propeller, and creates additional losses in the propeller efficiency.

Cavitation is in consideration of in this research however it will not be investigated

thoroughly.

The last influence which affects the propeller is due to acceleration of the vessel, the

engine will increase RPM, the pitch angle will increase or both at the same time. All

these actions are ways to increase the advance velocity of the vessel; the energy

conversion is done by loading the propeller, i.e. generating more thrust in order to get

a higher translational speed, until the ships resistance is equal to the delivered thrust.

During acceleration attention has to be given to the engine power envelope, e.g. if

the ship is sailing dead slow ahead, and the telegraph is set to full ahead the pitch

and RPM will try to fulfil this demand. The ship however has a high moment of inertia

and therefore will take time to accelerate. During this period the torque delivered to

the propeller is extremely high due to the low velocity of advance. The engine will

give 100% fuel rack and will be overloaded during this period due to the turbo lag see

‘Figure 9: Power envelope’. This situation should be avoided at all times and

therefore engine delay programmes are installed. The engine delay programmes are

in consideration however will not be investigated thoroughly.

What are Sea Margin and Engine Margin?

Sea Margin or Powering Margin can be defined as the margin which should be added

to the estimation of the speed-power relationship for a newly built ship in ideal

weather conditions to allow for the operation of the ship in realistic conditions

(Predicting Powering Margins, 2005). Classification societies have no regulations

regarding the sea margin and therefore a rule of thumb prediction is used, this

usually recommends approximately 15% sea margin. This however might be possible

to optimise; the Sea margin should be defined by the ships operator and designer by

means of defining the operating condition, to define the operating conditions the

environmental influences have to be established. Influences that should be

considered are: displacement, wind, waves, fouling, ice etc.

Engine Margin or Engine Operation Margin describes the mechanical and the

thermodynamic power reserve for the economical operation of the engine(s) with

respect to reasonably low fuel and maintenance costs (Predicting Powering Margins,

2005). The Engine Margin should be defined by the ships operator, by optimising

specific fuel consumption of the engine according to the ships mission profile. This

margin is normally 10 to 15% of MCR and this makes the CSR point.


What parameters influence the operating point of a combinator?

A combinator is designed to operate at a ship specific mission profile, during this

mission profile there are several factors which will prevent the ship from operation in

the optimum efficiency design point of the combinatory diagram. The major influential

factors are weather and environment as described above. Below is a line diagram of

the influential factors for the Combinator operating point see ‘Figure 12: Interaction of

components’.

(Grimmelius & Stapersma, 2003)

Figure 12: Interaction of components

This line diagram represents a ship, showing three influences which affect the ships

dynamics. The first influence is the command or ‘lever demand’ this is directly

connected to the combinatory diagram. The second is disturbances due to ship

resistance, this is related to waves, wind, ice, steering, drift and ships speed. The

final influence is in the ships wake field, disturbances are due to added resistance in

waves, shallow water, and fouling. As it shows the disturbances from outside are

indirectly connected to the engine control system and pitch control system. Some

disturbances are varying over time or can be very dynamic in nature.

What is the effect of propeller design conditions on the layout of the combinator?

Highly dependent on the combinator design is the propeller design, the diameter,

pitch, type and blades. The engine rpm and power are as the power envelope

describes limited, therefore the propeller pitch might not be allowed to the maximum


pitch at the minimal engine RPM. Also the design point(s) of the propeller are

dictating for the course of the combinatory curve. If the propeller design point is

chosen at MCR in trail condition, the vessel is likely to be overloaded in service

conditions. However if the propeller is designed for trail conditions (which is often the

case) the ship might be less efficient in service conditions. Therefore it seems like the

best manner of designing a ship is based on service conditions, taking into account

that hull fouling and sea state may vary thus a margin needs to be applied. If the

propeller pitch changes, the operating point will shift according to the combinator

curve, implying that the operating point in the power envelope also differs. In total the

effect of the design point(s) of the propeller dominates the layout of a combinator.

How is the dynamic response of the combinator in relation to the complete power

train?

Since the combinator is a software programmed system, the engine and CPP need

to be controlled. In all controllers there is a response time or ‘dead time’ in which the

system needs to calculate and send out a signal before the system reacts. Also

mechanically there is a response time; e.g. the time it takes to adjust the fuel rack

from position a to b, effectively this means that when a deviation of the desired

setting is present, it takes time before the desired setting is reached. This time is

critical in some situations where the load fluctuation is rapidly changing. The main

issue is resonance of the system; a ship operates in many different weather

conditions which imply that load changes are also inconsistent. In heavy seas the

propeller pitch may be reduced to prevent the engine from overloading, this pitch

change results in a different load on the engine, which in turn will change the fuel

rack position to limit the fuel and the engine output so constant RPM can be

maintained. During this controlling period the propeller load has already changed into

a different condition due to the change in draft and speed. This will result in a

different pitch and fuel rack setting, if the system is unable to respond in time the

possibility exists that engine and propeller will counteract. In this situation the engine

might have reduced load to avoid over speed, while the propeller is still increasing

pitch due to the lower resistance which will decrease engine speed and may cause

an engine stop. To avoid aforementioned problem from happening the load control

will interact. ‘The load control checks in a timeframe of thirty seconds how many

times the engine has been overloaded, if this is more than three times within this

timeframe the pitch will automatically be reduced by 2%. If the load limit is again

three times reached within thirty seconds, the pitch is again reduced by 2%. When

the engine is not overloaded anymore within the thirty second time span

automatically the pitch will be increased by 2% until the pitch is equal to the set

value’ (Corput, 2013).


How does the combinatory interact with the control system parts such as load control

and fuel rack?

The total control system is an elaborate piece of equipment requiring a lot of specific

knowledge on controls. Only the basics will be described in this literature study since

it only a small part of this research. To be able to explain the system in a structured

manner the system is divided into components which interact with each other.

Control handle

The system starts with the control handle which is positioned on the bridge, with this

lever the ship will change speed (or at least due to the systems behind it). The

handle has twenty-one positions; ten positions ahead, stop and ten positions astern.

These handle positions correlate to different engine rpm’s and different pitch angles.

Rate limiter

The control handle is connected to the rate limiter by means of an electrical signal.

The rate limiter regulates the up-ramping of the signal. This is done to avoid

overloading of the engine. The rate limiter is set up to the restrictions set by the

engine manufacturer regarding maximal engine loading speed. The first couple of

handle positions will result in a high up-ramping signal while the latter ones will

increase the load slowly; this is done for manoeuvring purposes.

CPP and RPM functions

The rate limiter is connected to the CPP control system and to the engine control

system. Both have a build in function, the CPP correlates the input signal (handle

position -10 to +10) to the corresponding pitch setting (-10 to +10). The output signal

could be 5 at input signal 2 or output -4 at input -2; this only applies to the CPP

system implying that the CPP system could turn ‘zero’ or ‘negative’. The engine RPM

function is just like the CPP system not necessarily a linear function, the input signal

(handle position) could be -1 while the output signal is 2 or input 6 with output 7.

However, the RPM output signal is required to be positive (0 to +10), due to the

inability to reverse rotation. The Combinator curve is in the combination of the CPP

and RPM function at certain control handle positions.

Load control

The load control input is connected to the engine RPM function and fuel rack

position, the output is connected to the pitch function. The load control has a build in

function of the power envelope. The RPM and fuel rack position combined result in

the operating point of the power envelope. If the operating point is outside the

operational area (load limit), the load control output will become lower than the

demanded pitch setting. The system also has a built in comparator, when the pitch

setting is higher or equal to the load control setting the signal will be reduced to the

load control signal. This system will ensure that the engine will not be overloaded for


extended periods. Of course the system is much more elaborate, however the scope

of the research is limited.

The load control system also interacts with the engine governor, the engine governor

receives its signal form the engine control module which is connected to the load

control module. The governor compares the demanded fuel rack position with the

current position and adjusts the fuel rack appropriately. This is done via a connecting

rod and hydraulic actuator. This hydraulic actuator is necessary to reach the

maximum stroke length of the fuel rack and to deliver sufficient force to adjust it. Due

to the hydraulic actuator the governor module is made a lot smaller than when it is

coupled directly to the fuel rack (Maanen, 2000).

How is the combinator curve affected by different drive train configurations?

The ship can be designed by means of different approaches and regulations, some

regulations or demands require the need for different drive train concepts. The drive

train concepts are mainly based on the needs of a vessel for instance ‘dynamic

positioning’ (DP). In the DP situation the drive train needs to be able to stay in

position regardless of the circumstances. This requires a special drive train concept,

which demands a lot from the engine(s) and propulsor(s). For this reason a special

combinator curve might be necessary to cope with the special demand of the

propulsor. This implies that the system has to use multiple combinator curves, for

free sailing, DP mode and special operation mode. To do so these combinator curves

need to be calculated and inserted into the control module, with the possibility to

switch between them.

Are there general guidance rules on the combinatory layout?

International Maritime Organisation (IMO) is the regulating body of international

regulations; all member states need to comply with these regulations. The IMO has

stated that: ‘Special consideration shall be given to the design, construction and installation of

propulsion machinery systems so that any mode of their vibrations shall not cause undue stresses in

this machinery in the normal operating ranges.’ (IMO, 1998). In many cases the class bureaus

have their own more strict regulations e.g. ‘Figure 13: Bureau Veritas regulation’,

these more strict regulations differ with each class bureau.

Figure 13: Bureau Veritas regulation

In this example the IMO states that the critical speeds are not allowed to be in the

normal operational area, while the Class Bureau demands an automated device to

prevent operation in this area. Finally the sea trails have to prove that the product

behaves according to the specifications, for sea trails a special protocol is in place

which needs to be completed satisfactory in order to get the necessary approvals.


What are Ice Class Requirements?

Ice Class is an additional requirement for ships which do operate in ice conditions,

the ice class notations differ from each other. There are the IMO ice class regulations

and the Finnish Swedish Ice Class Rules (FSICR). The different notations are based

on the ice thickness the ship can handle, and the age of the ice Figure 14: Baltic Ice

Class and IMO Polar Class

Courtesy of: (Magnus Eger & Mejlæander-Larsen, 2012)

Figure 14: Baltic Ice Class and IMO Polar Class

These notations are not only for the hull structure, but also require a certain

installation capacity. From a combinator design point of view only the additional drive

train requirements are interesting, and therefore will only be covered.

Figure 15: IMO Polar Class area shows the IMO polar class area, in this area,

dependent on the time of year a certain polar class notation is required for the vessel

to operate in this area.


Courtesy of: (Magnus Eger & Mejlæander-Larsen, 2012)

Figure 15: IMO Polar Class area

The ice resistance can be explained as described by (Juva & Riska, 2002) ‘The total

resistance is normally divided into open water resistance and level ice resistance.

The open water resistance is considered low at ice breaking speeds.’

For the ice resistance can be stated as follows:

‘The ice resistance is further divided for brash ice into two components, one to

breaking the ice and displacing it down and sideway’s and the other due to friction

along the parallel midbody.’

The ice resistance is also dependent on the type, two types of ice can be identified:

level ice (consolidated ice)

channel ice (brash ice)

Level ice is a solid mass which is not yet broken. The thickness is almost constant

and therefore the resistance is rather constant as well.

Channel ice is already broken once, and is not constant in thickness, assumed is that

the middle part of the channel is less thick than the sides. The slope at which the

thickness increases towards the edge of the channel is believed to be 2°. The

resistance is therefore inconsistent throughout the channel.


Verification and validation

Verification or ‘establishment of the correctness of a theory’ (Collins, 2003) is a difficult part

of the research, since reliable documentation on this subject is scarce. In this research the

purpose to identify the constraints in making a combinatory diagram and verify them will pose

a challenge, however, the creation of simulation models will identify the areas where

restrictions apply. Validation or ‘To establish the soundness’ (The American Heritage, 2000)

is necessary to prove the accuracy of the simulation programme. Validating the simulation

programme will be done by manually calculating several design points of the combinator

curve.

Date post:	04-Dec-2021
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