![Energy Efficient Ships, 23-24 November 2016, London, UK
© 2016: The Royal Institution of Naval Architects
SHIP POWERING PERFORMANCE – LEARNING FROM THE CHALLENGES FACED
BY OWNERS
L Karaminas and T Shen, American Bureau of Shipping
SUMMARY
Depending on the stakeholder’s focus, the term “performance” can be identified with single or multiple criteria, such as
powering, stability, comfort, vibrations, motions, propulsion in ice and more. This paper focuses on the powering
performance aspect. It describes and illustrates the application of a decision support system and its associated
complexities as well as a shipping company’s needs and typical actions. The paper explores recent challenges that have
been faced by owners. In the context of this paper, the term “Owner” infers ship owners, managers and operators.
Leveraging the lessons from the Greek shipping community, this paper provides an overview of best practices and
recommendations regarding technical specification, model tests, construction and trials, after trials, service, retrofit,
modifications and supporting tools. The need for calibrated performance reference values for use in service is also
discussed.
1. INTRODUCTION
In his seminal paper on “Ship Service Performance
Analysis”, Prof Telfer wrote [1]:
Probably at no time have the shipowner and his
technical advisers been faced with so many alternative and
additive means of improving the propulsive economy of
merchant ships than is the case to-day. Such alternatives
naturally sub-divide themselves into two broad classes: those
intended for engine improvement or the generation of power,
and those devoted to hull and propeller improvement or the
utilisation of power. The acid test of their efficacy applied by
the shipowner is reduction of fuel consumption for given speed,
or increase of speed on the same fuel consumption. Engineers,
however, are inclined to submit pounds per horse-power hour
as the test of engine economy, whilst the naval architect
endeavours to insist that only power and speed should influence
the reviewing of hull economy. Both are right, of course, but in
an imperfect world the last word is with the shipowner who
asks with some force and considerable truth, “of what use is
low pounds per horse-power -whatever that may be- or low
power, if the fuel consumption of my vessel is still far too
high?” This challenge can only be met by engineer and naval
architect sinking their differences -which are not hypothetical-
and coming to agreement on the true average power developed
by the engines and hence required by the ship. There should be
no need here to emphasize that the majority of indicator cards,
all generally of the peak variety, returned by sea-going
engineers and received by superintendents, are, taken at their
face value, utterly spurious either as a guide to engine economy
or to the standard of hull performance, there should be no need
to emphasise that abstract logs can serve other purposes than
merely wasting an engineer’s leisure or lumbering a
superintendent’s office; and that finally, progress is only
achieved by a thorough analysis of accurately recorded
experience.
Although Prof. Telfer presented this paper in 1929, the
same performance challenges are still faced by Owners
today.
2. THE CHRONIC GAP
There is a chronic gap between (a) the Chartering and
Operations Department and (b) the Technical
Department of a company, with the former demanding
information on current and expected future performance
of the ship and the latter struggling to evaluate and
predict ship performance under differing speed, draft and
environmental conditions.
For an Owner to continue making the right decisions for
hull-machinery maintenance and chartering-operations,
the shipboard measurements should not only be properly
conducted but, equally important, properly evaluated.
As this chronic gap varies in different companies, so
does the level of ship service performance evaluation and
the decision support system adopted. See Figure 1.
Figure 1: Representative decision support system
Operators invariably implement procedures and
incorporate mathematical models, in order to address
Fuel Efficient Operations. The mathematical models
selected depend on the complexity of the technical
aspect, as well as the technical knowledge and](https://image.slidesharecdn.com/shippoweringperformancelearningfromthechallengesfacedbyowners-170224091631/85/Ship-powering-performance-learning-from-the-challenges-faced-by-owners-1-320.jpg)
![Energy Efficient Ships, 23-24 November 2016, London, UK
© 2016: The Royal Institution of Naval Architects
When the target LRM is not achieved at tests, then the
designer makes a modification of the propeller’s pitch.
Such modification infers reduction of the pitch in order
to increase the LRM.
As a general approximation, 1.5% pitch decrease is
needed to increase rpm by 1%. As figure 7 illustrates,
for small changes in pitch, with other parameters
remaining constant, we can expect no adverse impact on
the power requirement.
Figure 7: Area for propeller pitch adjustment without
adverse impact on power.
4.2 (f) Trim
The subject of the so called “trim optimisation” is in
some cases considered by Owners as part of the model
tests. Trim optimization studies may also be carried out
with Computational Fluid Dynamics (CFD) simulation
and/or with model tests. The intent is to have sufficient
information for calculating a trim, under a given
condition, with the least powering requirement.
Facilities tend to provide Speed-Power at different Draft-
Trim scenarios or Trim-Power at different Speeds per
Draft, at calm sea. Owners can get the data in the format
they want, whilst there are tools available for quick and
easy trim guidance.
Owners ideally need the ISO-Power for different draft &
trim combinations, at different speeds, calibrated with
full scale measurements when these become available.
Figure 8 illustrates the ISO-power trends with the
objective to identify feasible positions with reduced
power requirement, subject to regulatory and operational
constraints.
Figure 8: ISO-Power curves at a specific speed.
Owners have advised that they used to receive
information mainly in graphic format, however in recent
times the designers are also providing same in tabular
format.
Often, due to the development cost of the necessary
information, the subject is explored when addressed in a
specification.
Owners consider the subject from an end-user’s
perspective, rather than just a study or a report. During
operation, any step in achieving the new trim for
reducing propulsion consumption, will mandate the
parallel assessment for compliance with applicable
statutory regulations and other operational criteria. For
this reason, it is recommended for Owners to consider
integrated software solutions, such as loading
instruments, assessing safety at each step.
4.2 (g) Propeller Cavitation Test
Regarding propeller cavitation, according to ITTC [2]:
the cavitation occurs near the blade tip, at the top of the
disk, in such case, a location of 0.8 to 0.9R at the top of
the propeller disk would be selected to match model and
full scale cavitation number.
Owners have advised that propeller cavitation tests are
carried nowadays with a similarity at a level of 0.7R to
0.75R. This may influence the predicted pressure
pulsation amplitude at different harmonics [3].
4.3 DURING CONSTRUCTION AND TRIALS
4.3 (a) Coating
Coating technology has improved over the past decade
but still the full scale prediction retains a fixed average
hull roughness value, same as in 1980’s. Owners have
advised that they may select an optimum coating at extra
cost and would like to see this reflected in the predicted
powering performance at sea trials.
P/D
EAR
Power
Index
Area for pitch
adjustment
without adverse
impact on power
V1
P3 > P2 > P1](https://image.slidesharecdn.com/shippoweringperformancelearningfromthechallengesfacedbyowners-170224091631/85/Ship-powering-performance-learning-from-the-challenges-faced-by-owners-5-320.jpg)
![Energy Efficient Ships, 23-24 November 2016, London, UK
© 2016: The Royal Institution of Naval Architects
In recent months, there were cases where Owners and
Builders jointly measured the hull roughness of
newbuildings prior launching and for several cases this
was below 80 µm. Figure 9 shows an example, where the
hull surface is divided in 120 patches with twelve Rt50
values taken per patch. Rt50 averages one min-max peak
within a one directional distance of 50 mm. The mean
hull roughness (MHR) of each patch is calculated, which
in turn results to an average hull roughness (AHR).
Figure 9: Example of a newbuilding hull surface grid
with MHR per patch, showing good homogeneity.
Therefore, the average hull roughness should be
systematically verified prior launching. The procedure
for measurements and derivation of the average hull
roughness merits standardization, as this will be
beneficial for research and service performance
monitoring purposes [4].
In the meantime, Builders have clarified that despite the
actual hull roughness can be determined, such value
cannot yet be considered in the prediction of powering
performance for the trial condition due to the fact that the
correlation factors are still based on older nominal
values, such as 150 µm all these years. Therefore, this
remains an area of future research.
4.3 (b) Wet Tables
Owners have advised of tank volume table discrepancies
being realized during service, especially for the
intermediate tank levels under trim/list. Therefore, tank
geometry and volume tables should be documented for
all fuel oil tanks to enable accuracy of calculations under
trim/list during service [5].
4.3 (c) Specific Fuel Oil Consumption
Owners have reported that the Specific Fuel Oil
Consumption (SFOC) of main engine, derived from Shop
Tests at ISO condition, may deviate from the one derived
during Sea Trials.
According to the study of T. Kida and T. Harada [6] from
nineteen very large crude carriers (VLCC), the relative
increase of SFOC at sea trials was observed from 4 to 7%
with an average of +5.2%. In the same study, the
primary factors were considered to be the different fuel
oil used and the fluctuation of engine load.
The main function of the governor is to limit the speed of
the engine by controlling the rate of fuel delivery.
However, the governor provides a certain volumetric
flow rather than a mass flow. The root cause of the
observed SFOC deviation is the governor and the fuel oil
for which the governor is set up. With the recent
introduction of electronically adjusted governors,
Owners are likely to see the SFOC deviation reduced, as
opposed to the conventional mechanical type governors
found in most existing ships.
The other point Owners have reported is that they are
aiming to extend the confirmation of the SFOC at ISO
condition during shop tests, from a single power level to
a power range representing a realistic operational profile.
4.3 (d) Shaft Torque Meter
Owners have advised that it would be beneficial for all
parties concerned that the shaft torque meter which is
utilized during sea trials measurements and subsequent
analysis, to remain on board. In this way, the in-service
measurements for performance evaluation and reporting
as required by Regulations and for Operational purposes,
will be carried out consistently.
4.4 AFTER TRIALS
Owners have advised that usually one of the deliverables
after the sea trials is a comparison of the predicted with
final corrected values.
A case study of two sister ships can be seen in figures 10
and 11. The power-speed values are matching, whereas
the rpm-speed values exhibit a deviation.
Figure 10: Case Study Suezmax Oil Tanker. Brake
Power.
STARBOARD
1 68 83 76 73 76 78 77 79 75 85
2 75 66 69 76 71 73 81 68 74 81
3 80 74 82 74 74 71 71 72 85 90
4 85 73 88 72 78 68 80 68 83 88
5 75 65 74 80 72 80 71 84 78 87
6 86 62 70 71 79 72 71 77 78 90
ZONE 10 9 8 7 6 5 4 3 2 1
PORT
1 86 85 85 81 80 94 76 73 78 81
2 79 94 83 83 74 72 81 68 80 71
3 75 78 89 85 90 75 73 81 83 81
4 72 71 79 88 75 72 71 74 78 81
5 67 91 85 87 75 77 81 75 80 80
6 73 83 85 87 83 78 83 80 71 83
ZONE 10 9 8 7 6 5 4 3 2 1](https://image.slidesharecdn.com/shippoweringperformancelearningfromthechallengesfacedbyowners-170224091631/85/Ship-powering-performance-learning-from-the-challenges-faced-by-owners-6-320.jpg)
![Energy Efficient Ships, 23-24 November 2016, London, UK
© 2016: The Royal Institution of Naval Architects
Figure 11: Case Study Suezmax Oil Tanker. RPM.
4.4 (a) Calibration
Following sea trials, Owners have been advising that it is
essential to have the powering performance calibrated.
This infers that all tables of Speed-Power-RPM at
different conditions, speeds, etc., to be finalized, taking
into account sea trials findings.
For instance, STAIMO [7] includes both the predicted
reference values from model tests, as well as the
resulting reference values (speed, power, rpm) with and
without sea margin, at a specific condition.
4.4 (b) Standardisation
The speed-power-rpm datasets contains a wealth of
information and merit to be standardized in a document
for each vessel. In addition, a reference operational
envelope for service conditions should be prepared and
this document should also be standardized and stay on
board too. The document should also include the
average hull roughness prior launching.
All this information will assist any prospective operator
with the monitoring of the vessel’s performance as well
as decisions regarding hull cleaning and coating during
service.
4.5 DURING SERVICE
By now a variety of issues which most Owners describe,
relate to necessary information for performance
monitoring during service.
Nowadays, Owners take delivery of newbuildings or buy
second hand vessels, and they then have to start their
own R&D. In all other transportation industries, the
operator knows in advance the asset’s performance
reference values for actual conditions.
Owners are forming performance departments with naval
architecture and marine engineering resources, in order
to develop something that ought to be available prior
taking the ship in service.
4.6 RETROFITS AND MODIFICATIONS
To improve vessel performance, Owners may implement
an Energy Saving Device (ESD). Whether the ESD is
for a newbuilding or a ship in service, the Owner faces
the following dilemmas:
• Given the uncertainty and differences between
testing facilities, how is the alleged gain taking
into account parametric variations (draft,
speed, etc.)?
• Given the uncertainty of the equipment and
method applied under which conditions, could
the gain be accurately measured and verified?
Owners have commented that there is not yet a formal
procedure for the correction of wake for a Duct ESD. A
method has been discussed within the 1999 ITTC and
tentatively accepted for evaluation of pre-swirl stator
concepts. The wake scaling presumes that tests with the
same propeller but without the stator have been
performed as well.
In some cases where the hull lines and propeller have
undergone several design cycles for improving the
efficiency, the alleged gain of such devices may not even
be easy to spot during service. Worth noting that any
theoretical gain in calm sea, is reduced in service due to
prevailing environmental conditions.
The installation of a duct reduces the Light Running
Margin (LRM) as the propeller is further loaded. This is
illustrated in Figure 12.
Figure 12: Case study Suezmax Oil Tanker. LRM with
and without duct, at different average hull roughness.
4.7 TOOLS FOR VESSEL PERFORMANCE
The state of affairs as described so far has given rise to a
variety of software providers. Owners commented on the
need for such software solutions to be:
• Proven with objective evidence
• Transparent
• Practical
• Accurate and Reliable
Moreover, Owners want to safeguard themselves against
weather services claims, resulting to speed and/or
consumption claims using formulae with unknown
supporting documentation.
The instrumentation used for measurements during
service is based on different technologies which need to
be appreciated by Owners prior implementation. Owners
LRM (%)
AHR (micron) 100 150 200 100 150 200
Scantling Draft 2.79 2.11 1.77 4.11 3.45 2.96
Design Draft 3.72 3.19 2.78 4.01 3.52 3.17
Ballast Draft 4.22 3.62 3.16 4.33 3.84 3.48
With Without](https://image.slidesharecdn.com/shippoweringperformancelearningfromthechallengesfacedbyowners-170224091631/85/Ship-powering-performance-learning-from-the-challenges-faced-by-owners-7-320.jpg)
![Energy Efficient Ships, 23-24 November 2016, London, UK
© 2016: The Royal Institution of Naval Architects
have been advising their preference on instrumentation
such as torque-meter, fuel flow-meters, speed-logs to be
standardised in terms of specification, minimum levels of
accuracy and repeatability and to be pre-installed on
ships as standard equipment prior sea trials and delivery.
5. CALIBRATED PERFORMANCE
REFERENCE VALUES FOR USE IN
SERVICE
To this day, the scope of model tests has been defined
and agreed between the Builder and the Facility. In
addition, it is neither a Statutory nor a Class requirement
for model tests reports to be provided as a standard
document satisfying a minimum common scope per ship
type/size/operation. Builders in Korea and China are
now sharing full model test reports with Owners.
Therefore, there is need for agreement on what
information will be provided to the Owner, from the
defined Scope of Work to the Deliverable.
Now let us assume that the scope of tests would have
been comprehensive and that an ideal situation has been
reached, where the predictions from facility to facility
would vary within acceptable tolerances, and that the
Builder and Owner would agree on all the appropriate
information to be shared. Well, even in such scenario,
the issue will become how will that information, which
by default is limited to just a few nominal drafts and
speeds can be processed in order for Owners to have
Performance Reference Values for actual conditions
within an operational envelope. For instance, the
operational envelope could be defined by a range of
speeds, drafts, trims and weather.
There is a variety of methods available for the derivation
of the predicted powering reference values. Some being
more complex than others. Figure 13 provides a
comparison overview of such methods, whilst a brief
description is provided further down.
Figure 13: Comparison overview of methods applied for
the derivation of powering reference values.
Irrespective of the method selected to be applied, an
essential process in the matter is the Calibration, where
the predicted powering reference values for actual
conditions are correlated with actual quality
measurements taken during Sea Trials and Service.
5.1 RESISTANCE DECOMPOSITION
With this method, reference values are estimated for
different resistance components, such as at calm sea,
added wind, wave, steering, drifting, effects due to
shallow waters, temperature, cavitation, aeration, etc.
Having determined the overall component in actual
conditions and by applying decomposition and
normalisation to a specific draft, trim and speed
condition, the resistance component due to the increase
of roughness could then be estimated.
Over the past century, researchers have grappled with the
challenges in predicting added resistance in actual
conditions, which in turn need to be converted to power,
let alone the confidence of the outcome of the
calibration.
5.2 CFD SIMULATION (CFD)
Whilst CFD is mostly known for design improvement
and forensic purposes, CFD is also used in the
preparation of full scale powering reference values in a
database, reflecting a wide range of operational -draft,
trim, speed- and environmental conditions.
CFD can complement the information already derived
from model testing at towing tank facilities and can
populate the points of a database.
Recent advances in CFD technology enable designers to
further explore the full scale powering predictions for
various operating profile conditions [8].
5.3 ARTIFICIAL NEURAL NETWORKS (ANN)
With this method, reference values can be estimated on
an ongoing basis, subject to sufficient quality
information and measurements and then compared to
actual measurements.
ANN work on the basis of input (measured) and output
(predicted) data sets. For powering models, the ANN is
trained with a large number of data sets, each consisting
of a large number of parameters. Calibration takes place
through the training process.
Subsequently, a trained ANN, having established the
relationships between input and output, allows the
comparison of in-service future quality measurements
with their powering reference values under actual
conditions. As it is a black-box approach, there may be
some drawbacks.
Method
Relative…
...cost to Owners Medium High High Low Low
...number of parameters
required
High High High Low Low
...effort required for
preparation of reference
values
Medium High High Low Low
...effort required for
calibration of reference
values
High High High Medium Low
...effort required for
performance assessment
against Charter Party
High High High Medium Low
...effort required for
Optimum Voyage
Planning
High - Medium - Medium
...effort required for
identifation of hull
coating degradation
High - Medium Low -
...effort required for
identifation of engine-fuel
system degradation
High - Medium - Low
Resistance
Decomposition
CFD
Simulation
Artificial
Neural
Networks
Residual
Service
Margin
Slip](https://image.slidesharecdn.com/shippoweringperformancelearningfromthechallengesfacedbyowners-170224091631/85/Ship-powering-performance-learning-from-the-challenges-faced-by-owners-8-320.jpg)
Ship powering performance – learning from the challenges faced by owners
- 1. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects SHIP POWERING PERFORMANCE – LEARNING FROM THE CHALLENGES FACED BY OWNERS L Karaminas and T Shen, American Bureau of Shipping SUMMARY Depending on the stakeholder’s focus, the term “performance” can be identified with single or multiple criteria, such as powering, stability, comfort, vibrations, motions, propulsion in ice and more. This paper focuses on the powering performance aspect. It describes and illustrates the application of a decision support system and its associated complexities as well as a shipping company’s needs and typical actions. The paper explores recent challenges that have been faced by owners. In the context of this paper, the term “Owner” infers ship owners, managers and operators. Leveraging the lessons from the Greek shipping community, this paper provides an overview of best practices and recommendations regarding technical specification, model tests, construction and trials, after trials, service, retrofit, modifications and supporting tools. The need for calibrated performance reference values for use in service is also discussed. 1. INTRODUCTION In his seminal paper on “Ship Service Performance Analysis”, Prof Telfer wrote [1]: Probably at no time have the shipowner and his technical advisers been faced with so many alternative and additive means of improving the propulsive economy of merchant ships than is the case to-day. Such alternatives naturally sub-divide themselves into two broad classes: those intended for engine improvement or the generation of power, and those devoted to hull and propeller improvement or the utilisation of power. The acid test of their efficacy applied by the shipowner is reduction of fuel consumption for given speed, or increase of speed on the same fuel consumption. Engineers, however, are inclined to submit pounds per horse-power hour as the test of engine economy, whilst the naval architect endeavours to insist that only power and speed should influence the reviewing of hull economy. Both are right, of course, but in an imperfect world the last word is with the shipowner who asks with some force and considerable truth, “of what use is low pounds per horse-power -whatever that may be- or low power, if the fuel consumption of my vessel is still far too high?” This challenge can only be met by engineer and naval architect sinking their differences -which are not hypothetical- and coming to agreement on the true average power developed by the engines and hence required by the ship. There should be no need here to emphasize that the majority of indicator cards, all generally of the peak variety, returned by sea-going engineers and received by superintendents, are, taken at their face value, utterly spurious either as a guide to engine economy or to the standard of hull performance, there should be no need to emphasise that abstract logs can serve other purposes than merely wasting an engineer’s leisure or lumbering a superintendent’s office; and that finally, progress is only achieved by a thorough analysis of accurately recorded experience. Although Prof. Telfer presented this paper in 1929, the same performance challenges are still faced by Owners today. 2. THE CHRONIC GAP There is a chronic gap between (a) the Chartering and Operations Department and (b) the Technical Department of a company, with the former demanding information on current and expected future performance of the ship and the latter struggling to evaluate and predict ship performance under differing speed, draft and environmental conditions. For an Owner to continue making the right decisions for hull-machinery maintenance and chartering-operations, the shipboard measurements should not only be properly conducted but, equally important, properly evaluated. As this chronic gap varies in different companies, so does the level of ship service performance evaluation and the decision support system adopted. See Figure 1. Figure 1: Representative decision support system Operators invariably implement procedures and incorporate mathematical models, in order to address Fuel Efficient Operations. The mathematical models selected depend on the complexity of the technical aspect, as well as the technical knowledge and
- 2. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects experience of those who are called to use these models for decision support. See Figure 2. Figure 2: Complexities of Fuel Efficient Operations Fuel Efficient Operations depend on the Owner’s ability to introduce evaluation procedures which will trend effectiveness, improve performance, establish and maintain the ship-specific Fuel Influencing Factors. Optimum Voyage Planning is a mathematical optimisation process that yields recommended voyage leg speeds, for virtual arrival and overall minimum fuel consumption. It should not be confused with Weather Routing, Bunkers Management or Voyage Management, which are a must too. Optimum Voyage Planning is usually sought by those with a direct commercial interest on the cargo and passengers transported. For optimum voyage planning the fuel influencing factors are a prerequisite. As Figures 1 and 2 illustrate, this is a complex subject where Owners can easily be drawn into continuous R&D in an effort to support the company’s vision and path. The vision typically represents an array of desired objectives and commercial values for the Owner, however the path should be in the following order: • Performance Reference Values • Monitoring & Evaluation • Fuel Influencing Factors • Optimum Operation A company would need to evaluate their: • commitment • people • training • procedures • equipment • tools The typical action plan of a company is proposed as follows: • Creation of dedicated performance department that is not involved with daily operations. It is recommended to identify development areas and to avoid setting high expectations, as there is a steep learning curve. Some steps could be towards Performance and Diagnostics for Hull- Propeller-Engine System and Ship Engineering Systems. • The dedicated performance department may start with just one or two persons, though more resources may have to be allocated, so as to avoid overloading this department prematurely. • The company will have to receive training and engage with experts, to ensure common understanding. • Since traditional noon report based performance evaluation has proven of varying quality for many Owners, focus may shift to automated measurement procedures. • A pilot project for at least a ship should be carried out as a testing platform for the procedures and all the equipment required. • Pilot tools will need to be developed by the performance department, in cooperation with the technical/operations/chartering departments. • Data and results are to be evaluated systematically. • The Plan-Do-Check-Act (PDCA) cycle should be conducted systematically until the technical hurdles are reduced to a manageable level and the results are acceptable for use in service. The potential benefits are: • Transparency in operational performance for self-assessment • Technically justified baseline reference values for comparison with actual performance values • Deviation and trending for fuel oil consumption • Alert of potential degradation rates or values • Technically acceptable daily fuel consumption for chartering purposes • Enhanced internal communications • Improved level of negotiation with charterers • Enhanced company’s technology image • Company’s ability to benchmark its own fleet in a systematic and consistent method • Enhanced company’s knowledge and planning with new construction projects 3. THE PRESENT STATUS The prediction of powering performance for commercial ships has been of limited specification, due to commercial motives, the costs involved with model tests and the lack of involvement by Owners in general. As a result, Owners only have access to performance data under specific nominal conditions rather than the full operational performance profile.
- 3. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects We are now in a period which somehow resembles the one when naval architects realised benefits by going progressively from the use of slide rule to the use of the early primitive spreadsheet. Numerical tools are now being widely explored and adopted by designers. There is still some way to go before some commonly accepted procedures can be established by those applying CFD simulation coupled with model testing. Typically, Owners are not familiar with all mathematical complexities, whilst there are no concrete guidelines for carrying out or verifying CFD. The constantly evolving regulatory landscape, with new requirements introduced by port and flag states, government agencies and charterers, is creating challenges for compliance. Through benchmarking and analysis of vessel and environmental performance, Owners can achieve environmental compliance while reducing operational costs. It is recommended to establish Key Performance Indicators (KPIs) to facilitate performance optimization. The approach should include a ship-specific propulsion model based on vessel design characteristics and powering characteristics obtained from model tests, sea trial data and other relevant sources. Leveraging a ship- specific model enables the definition of relevant performance baselines and improves decision making by more accurately reflecting true vessel operations. Based on the vessel model and analyses of regularly captured data, a set of KPIs for Vessel Performance can be established to enable decision support both on shore and aboard the vessel in the following areas: • Hull and propeller performance • Main Engine condition • Auxiliary Engine/Systems base load optimization • Vessel/fleet benchmarking of performance • Prediction/planning of fuel efficiency improvement measures 4. THE CHALLENGES FACED BY OWNERS During the vessel lifecycle, Owners are faced with challenges to define the specification for the following ship powering performance related items: • Technical Specification • Model Tests • Construction and Trials • After Trials • Service • Retrofit and Modifications • Tools Lessons learned together with applied best practices and recommendations are provided below. 4.1 DURING TECHNICAL SPECIFICATION 4.1 (a) Minimum Common Scope Owners have commented that technical specifications can be improved with regards to the scope of towing tank model tests and propeller cavitation tests. For commercial ships, the industry would benefit from a minimum common scope to be defined and applied systematically for different ship types. 4.1 (b) Sea Margin and Light Running Margin Much has been said in publications about the famous Sea Margin on power and the Light Running Margin on rpm. The light running margin should be agreed with the Builder and Engine designers. Ship-Engine designs have been de-rated, whilst the technical specification’s sea margin remained a percentage and not a justified absolute value. Figure 3 shows cases of Suezmax Oil Tankers. Worth noting that a ship with relatively lower power will suffer greater speed loss in weather. The objective of the sea margin is to account for the external environmental influences, namely: wind, waves, fouling. Figure 3: Different cases of specified sea margin for Suezmax Oil Tankers. Each component should be accounted with supporting calculations. a) Margin for wind is usually determined via wind resistance calculation. b) Margin for waves is usually determined via seakeeping calculation, using spectral analysis. c) Margin for fouling or increased roughness is rarely expressed as percentage. A service margin should be considered on the basis of numerical analysis, representing the ship’s anticipated operational profile during service. Figure 4 is an example of the service margin accounting for wind and waves as per (a) and (b) above, at design and ballast drafts of a Suezmax Oil Tanker.
- 4. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects Figure 4: Example of service margin of a Suezmax Oil Tanker due to wind and waves. In the era of ship efficiency, Owners are starting to appreciate this issue from a standpoint of need rather than good to have. For the majority of commercial ships, this infers that the ship could sustain its service speed over several realistic operational conditions, but not for all of them. Owners have welcomed the approach of some Builders who systematically provide thorough added weather resistance and powering calculations and hope for such analysis to be standardised for different ship types and sizes in future. 4.1 (c) Standards of Sea Trials Standards of sea trials appear to be another focus topic amongst Industry stakeholders. Owners recognise a growing need for transparent processes and tools to be reflected in a technical specification. ISO 15016:2015 and STAIMO tool have been welcomed. 4.1 (d) Minimum Propulsion Power Furthermore, the IMO is establishing criteria to determine the ship’s minimum power. The topics of both minimum propulsion power and manoeuvrability have always been of importance to Owners as they relate to ship safety, damages to ship and cargo, insurance claims, charter and image losses. 4.2 DURING MODEL TESTS 4.2 (a) Quality and Accuracy of Model Tests The quality and accuracy of model tests play a key role in the evaluation of full scale trials. For some ships, sea trials are carried out in a draft different than the contractual condition. For the conversion to the contractual condition, the model test predictions are used. Therefore accuracy and consistency are a must. Figure 5 illustrates an identical design being tested at two different tank test facilities where the differences are acceptable. Figure 5: Aframax Oil Tanker Case Study. 4.2 (b) Average Hull Roughness There are facilities which predict the full scale performance at hull roughness of 125 micron, whilst other facilities at 150 microns. Owners have advised that some facilities are providing a sensitivity analysis of the influence of the average hull roughness on the power and rpm. 4.2 (c) Deliverables An area of improvement would be the predicted Speed- Power-RPM values for a range of speeds, drafts and environmental conditions. 4.2 (d) Arrangements Figure 6 is an example layout with on-line PC/TV monitors in a facility. Owners have advised that certain facilities provide on-line information during testing. Figure 6: Example of arrangement with good access to on-line information during testing. 4.2 (e) Propeller Pitch Modification The subject of the propeller pitch modification after completion of tests should be appreciated. Technical specifications tend to refer to a minimum light running margin (LRM). In that respect, it is a common solution for designers to first consider the results from model tests and then modify the propeller pitch. Speed (knots) Facility 1 Power (kW) Facility 2 Power (kW) "Delta" 13 7669 7641 0% 14 9564 9392 -2% 15 11766 11453 -3% 16 14403 14077 -2% 17 17724 17599 -1%
- 5. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects When the target LRM is not achieved at tests, then the designer makes a modification of the propeller’s pitch. Such modification infers reduction of the pitch in order to increase the LRM. As a general approximation, 1.5% pitch decrease is needed to increase rpm by 1%. As figure 7 illustrates, for small changes in pitch, with other parameters remaining constant, we can expect no adverse impact on the power requirement. Figure 7: Area for propeller pitch adjustment without adverse impact on power. 4.2 (f) Trim The subject of the so called “trim optimisation” is in some cases considered by Owners as part of the model tests. Trim optimization studies may also be carried out with Computational Fluid Dynamics (CFD) simulation and/or with model tests. The intent is to have sufficient information for calculating a trim, under a given condition, with the least powering requirement. Facilities tend to provide Speed-Power at different Draft- Trim scenarios or Trim-Power at different Speeds per Draft, at calm sea. Owners can get the data in the format they want, whilst there are tools available for quick and easy trim guidance. Owners ideally need the ISO-Power for different draft & trim combinations, at different speeds, calibrated with full scale measurements when these become available. Figure 8 illustrates the ISO-power trends with the objective to identify feasible positions with reduced power requirement, subject to regulatory and operational constraints. Figure 8: ISO-Power curves at a specific speed. Owners have advised that they used to receive information mainly in graphic format, however in recent times the designers are also providing same in tabular format. Often, due to the development cost of the necessary information, the subject is explored when addressed in a specification. Owners consider the subject from an end-user’s perspective, rather than just a study or a report. During operation, any step in achieving the new trim for reducing propulsion consumption, will mandate the parallel assessment for compliance with applicable statutory regulations and other operational criteria. For this reason, it is recommended for Owners to consider integrated software solutions, such as loading instruments, assessing safety at each step. 4.2 (g) Propeller Cavitation Test Regarding propeller cavitation, according to ITTC [2]: the cavitation occurs near the blade tip, at the top of the disk, in such case, a location of 0.8 to 0.9R at the top of the propeller disk would be selected to match model and full scale cavitation number. Owners have advised that propeller cavitation tests are carried nowadays with a similarity at a level of 0.7R to 0.75R. This may influence the predicted pressure pulsation amplitude at different harmonics [3]. 4.3 DURING CONSTRUCTION AND TRIALS 4.3 (a) Coating Coating technology has improved over the past decade but still the full scale prediction retains a fixed average hull roughness value, same as in 1980’s. Owners have advised that they may select an optimum coating at extra cost and would like to see this reflected in the predicted powering performance at sea trials. P/D EAR Power Index Area for pitch adjustment without adverse impact on power V1 P3 > P2 > P1
- 6. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects In recent months, there were cases where Owners and Builders jointly measured the hull roughness of newbuildings prior launching and for several cases this was below 80 µm. Figure 9 shows an example, where the hull surface is divided in 120 patches with twelve Rt50 values taken per patch. Rt50 averages one min-max peak within a one directional distance of 50 mm. The mean hull roughness (MHR) of each patch is calculated, which in turn results to an average hull roughness (AHR). Figure 9: Example of a newbuilding hull surface grid with MHR per patch, showing good homogeneity. Therefore, the average hull roughness should be systematically verified prior launching. The procedure for measurements and derivation of the average hull roughness merits standardization, as this will be beneficial for research and service performance monitoring purposes [4]. In the meantime, Builders have clarified that despite the actual hull roughness can be determined, such value cannot yet be considered in the prediction of powering performance for the trial condition due to the fact that the correlation factors are still based on older nominal values, such as 150 µm all these years. Therefore, this remains an area of future research. 4.3 (b) Wet Tables Owners have advised of tank volume table discrepancies being realized during service, especially for the intermediate tank levels under trim/list. Therefore, tank geometry and volume tables should be documented for all fuel oil tanks to enable accuracy of calculations under trim/list during service [5]. 4.3 (c) Specific Fuel Oil Consumption Owners have reported that the Specific Fuel Oil Consumption (SFOC) of main engine, derived from Shop Tests at ISO condition, may deviate from the one derived during Sea Trials. According to the study of T. Kida and T. Harada [6] from nineteen very large crude carriers (VLCC), the relative increase of SFOC at sea trials was observed from 4 to 7% with an average of +5.2%. In the same study, the primary factors were considered to be the different fuel oil used and the fluctuation of engine load. The main function of the governor is to limit the speed of the engine by controlling the rate of fuel delivery. However, the governor provides a certain volumetric flow rather than a mass flow. The root cause of the observed SFOC deviation is the governor and the fuel oil for which the governor is set up. With the recent introduction of electronically adjusted governors, Owners are likely to see the SFOC deviation reduced, as opposed to the conventional mechanical type governors found in most existing ships. The other point Owners have reported is that they are aiming to extend the confirmation of the SFOC at ISO condition during shop tests, from a single power level to a power range representing a realistic operational profile. 4.3 (d) Shaft Torque Meter Owners have advised that it would be beneficial for all parties concerned that the shaft torque meter which is utilized during sea trials measurements and subsequent analysis, to remain on board. In this way, the in-service measurements for performance evaluation and reporting as required by Regulations and for Operational purposes, will be carried out consistently. 4.4 AFTER TRIALS Owners have advised that usually one of the deliverables after the sea trials is a comparison of the predicted with final corrected values. A case study of two sister ships can be seen in figures 10 and 11. The power-speed values are matching, whereas the rpm-speed values exhibit a deviation. Figure 10: Case Study Suezmax Oil Tanker. Brake Power. STARBOARD 1 68 83 76 73 76 78 77 79 75 85 2 75 66 69 76 71 73 81 68 74 81 3 80 74 82 74 74 71 71 72 85 90 4 85 73 88 72 78 68 80 68 83 88 5 75 65 74 80 72 80 71 84 78 87 6 86 62 70 71 79 72 71 77 78 90 ZONE 10 9 8 7 6 5 4 3 2 1 PORT 1 86 85 85 81 80 94 76 73 78 81 2 79 94 83 83 74 72 81 68 80 71 3 75 78 89 85 90 75 73 81 83 81 4 72 71 79 88 75 72 71 74 78 81 5 67 91 85 87 75 77 81 75 80 80 6 73 83 85 87 83 78 83 80 71 83 ZONE 10 9 8 7 6 5 4 3 2 1
- 7. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects Figure 11: Case Study Suezmax Oil Tanker. RPM. 4.4 (a) Calibration Following sea trials, Owners have been advising that it is essential to have the powering performance calibrated. This infers that all tables of Speed-Power-RPM at different conditions, speeds, etc., to be finalized, taking into account sea trials findings. For instance, STAIMO [7] includes both the predicted reference values from model tests, as well as the resulting reference values (speed, power, rpm) with and without sea margin, at a specific condition. 4.4 (b) Standardisation The speed-power-rpm datasets contains a wealth of information and merit to be standardized in a document for each vessel. In addition, a reference operational envelope for service conditions should be prepared and this document should also be standardized and stay on board too. The document should also include the average hull roughness prior launching. All this information will assist any prospective operator with the monitoring of the vessel’s performance as well as decisions regarding hull cleaning and coating during service. 4.5 DURING SERVICE By now a variety of issues which most Owners describe, relate to necessary information for performance monitoring during service. Nowadays, Owners take delivery of newbuildings or buy second hand vessels, and they then have to start their own R&D. In all other transportation industries, the operator knows in advance the asset’s performance reference values for actual conditions. Owners are forming performance departments with naval architecture and marine engineering resources, in order to develop something that ought to be available prior taking the ship in service. 4.6 RETROFITS AND MODIFICATIONS To improve vessel performance, Owners may implement an Energy Saving Device (ESD). Whether the ESD is for a newbuilding or a ship in service, the Owner faces the following dilemmas: • Given the uncertainty and differences between testing facilities, how is the alleged gain taking into account parametric variations (draft, speed, etc.)? • Given the uncertainty of the equipment and method applied under which conditions, could the gain be accurately measured and verified? Owners have commented that there is not yet a formal procedure for the correction of wake for a Duct ESD. A method has been discussed within the 1999 ITTC and tentatively accepted for evaluation of pre-swirl stator concepts. The wake scaling presumes that tests with the same propeller but without the stator have been performed as well. In some cases where the hull lines and propeller have undergone several design cycles for improving the efficiency, the alleged gain of such devices may not even be easy to spot during service. Worth noting that any theoretical gain in calm sea, is reduced in service due to prevailing environmental conditions. The installation of a duct reduces the Light Running Margin (LRM) as the propeller is further loaded. This is illustrated in Figure 12. Figure 12: Case study Suezmax Oil Tanker. LRM with and without duct, at different average hull roughness. 4.7 TOOLS FOR VESSEL PERFORMANCE The state of affairs as described so far has given rise to a variety of software providers. Owners commented on the need for such software solutions to be: • Proven with objective evidence • Transparent • Practical • Accurate and Reliable Moreover, Owners want to safeguard themselves against weather services claims, resulting to speed and/or consumption claims using formulae with unknown supporting documentation. The instrumentation used for measurements during service is based on different technologies which need to be appreciated by Owners prior implementation. Owners LRM (%) AHR (micron) 100 150 200 100 150 200 Scantling Draft 2.79 2.11 1.77 4.11 3.45 2.96 Design Draft 3.72 3.19 2.78 4.01 3.52 3.17 Ballast Draft 4.22 3.62 3.16 4.33 3.84 3.48 With Without
- 8. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects have been advising their preference on instrumentation such as torque-meter, fuel flow-meters, speed-logs to be standardised in terms of specification, minimum levels of accuracy and repeatability and to be pre-installed on ships as standard equipment prior sea trials and delivery. 5. CALIBRATED PERFORMANCE REFERENCE VALUES FOR USE IN SERVICE To this day, the scope of model tests has been defined and agreed between the Builder and the Facility. In addition, it is neither a Statutory nor a Class requirement for model tests reports to be provided as a standard document satisfying a minimum common scope per ship type/size/operation. Builders in Korea and China are now sharing full model test reports with Owners. Therefore, there is need for agreement on what information will be provided to the Owner, from the defined Scope of Work to the Deliverable. Now let us assume that the scope of tests would have been comprehensive and that an ideal situation has been reached, where the predictions from facility to facility would vary within acceptable tolerances, and that the Builder and Owner would agree on all the appropriate information to be shared. Well, even in such scenario, the issue will become how will that information, which by default is limited to just a few nominal drafts and speeds can be processed in order for Owners to have Performance Reference Values for actual conditions within an operational envelope. For instance, the operational envelope could be defined by a range of speeds, drafts, trims and weather. There is a variety of methods available for the derivation of the predicted powering reference values. Some being more complex than others. Figure 13 provides a comparison overview of such methods, whilst a brief description is provided further down. Figure 13: Comparison overview of methods applied for the derivation of powering reference values. Irrespective of the method selected to be applied, an essential process in the matter is the Calibration, where the predicted powering reference values for actual conditions are correlated with actual quality measurements taken during Sea Trials and Service. 5.1 RESISTANCE DECOMPOSITION With this method, reference values are estimated for different resistance components, such as at calm sea, added wind, wave, steering, drifting, effects due to shallow waters, temperature, cavitation, aeration, etc. Having determined the overall component in actual conditions and by applying decomposition and normalisation to a specific draft, trim and speed condition, the resistance component due to the increase of roughness could then be estimated. Over the past century, researchers have grappled with the challenges in predicting added resistance in actual conditions, which in turn need to be converted to power, let alone the confidence of the outcome of the calibration. 5.2 CFD SIMULATION (CFD) Whilst CFD is mostly known for design improvement and forensic purposes, CFD is also used in the preparation of full scale powering reference values in a database, reflecting a wide range of operational -draft, trim, speed- and environmental conditions. CFD can complement the information already derived from model testing at towing tank facilities and can populate the points of a database. Recent advances in CFD technology enable designers to further explore the full scale powering predictions for various operating profile conditions [8]. 5.3 ARTIFICIAL NEURAL NETWORKS (ANN) With this method, reference values can be estimated on an ongoing basis, subject to sufficient quality information and measurements and then compared to actual measurements. ANN work on the basis of input (measured) and output (predicted) data sets. For powering models, the ANN is trained with a large number of data sets, each consisting of a large number of parameters. Calibration takes place through the training process. Subsequently, a trained ANN, having established the relationships between input and output, allows the comparison of in-service future quality measurements with their powering reference values under actual conditions. As it is a black-box approach, there may be some drawbacks. Method Relative… ...cost to Owners Medium High High Low Low ...number of parameters required High High High Low Low ...effort required for preparation of reference values Medium High High Low Low ...effort required for calibration of reference values High High High Medium Low ...effort required for performance assessment against Charter Party High High High Medium Low ...effort required for Optimum Voyage Planning High - Medium - Medium ...effort required for identifation of hull coating degradation High - Medium Low - ...effort required for identifation of engine-fuel system degradation High - Medium - Low Resistance Decomposition CFD Simulation Artificial Neural Networks Residual Service Margin Slip
- 9. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects 5.4 RESIDUAL SERVICE MARGIN The objective of this method is to estimate reference values by determining the Residual Service Margin (RSM). The RSM is what is available at any given time towards the added resistance of wind, wave and roughness increase. Each ship has a specific service margin envelope when newly built (see Figure 4). During service the natural increase of roughness will reduce such capability, meaning that for the same speed and draft condition there will be an increased power requirement. Having derived the RSM, the new power reference values could then be re-calculated. Consistent filter for weather, draft and power range should be applied. Figure 14 illustrates the reduction of RSM due to increase of hull roughness over time. Figure 15 shows the power requirement at specific drafts and residual margins. Figure 14: Residual Service Margin (RSM) over Time. Figure 15: Case Study Kamsarmax Bulk Carrier. Power at different drafts and Residual Service Margin (RSM). 5.5 SLIP The objective of this method is to estimate reference values in actual conditions, inclusive of roughness increase and weather usually up to BF4/DSS3. Unlike the previous methods, with this one the engine and/or fuel system degradation could be the causal factors observed when the statistical deviation of actual values increases over time. For the calibration, there is a need for reliable measurements in actual conditions without the need to normalise to a draft at calm sea. Figures 16 and 17 illustrate calibrated values on the basis of the slip method. Figure 16: Case Study Suezmax Oil Tanker. Calibration with the measurements from sea trials, shown in dots. Figure 17: Case Study Suezmax Oil Tanker. Powering Reference Values after completion of calibration. Shipping is the only industry where the asset is rarely provided with Calibrated Performance Reference Values. Yet, Owners are required to manage their energy efficiency and whilst there are all kinds of problems with the measuring equipment, procedures and processing of the information, Owners still have no transparent approach to compare the measurements with calibrated NCR
- 10. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects reference values. This has resulted with Owners creating their own R&D departments, experimenting with various consultants and software. So one may ask, Is there a way to fix this so that each newbuilding starts to have the necessary information? The answer is, yes there is, provided the industry converges on the roadmap which needs to be followed. 6. CONCLUSIONS The importance for Owners to focus on the following cannot be over-emphasized: • Specification of Model Tests • Verification of a Ship's Powering Performance upon Delivery • Periodic Calibration of a Ship's Powering Performance Reference Values during Service • Quality Measurements during Service. In the meantime, Owners have been seeking a collaborative industry roadmap, leading to commonly applied standards, with actions including but not limited to: • Definition of minimum scope of model tests for the prediction of powering performance as well as the prediction of propeller cavitation. • Definition of how to verify all the correction factors used by model test facilities nowadays. • Convergence to a mandatory common testing methodology. • Definition of the minimum information to be included in a model test report and released to all parties concerned. • Definition of the methodology to be applied in order to derive the ship-specific powering reference values. • Definition of a standard procedure for the average hull roughness measurement and documentation prior launching and during service. • Definition of a standard set of equipment to be placed on board prior the sea trials and which will remain on board, inspected and maintained thereafter. • Definition of the procedure to be applied for minimum data collection during the initial sea trials as well as during service. • Definition of the calibration method in order to update the powering reference values for actual service conditions and the document to exist per vessel. We all need to learn from each other, share openly the experiences and find ways to positively improve ship efficiency and contribute in the reduction of emissions. 7. ACKNOWLEDGEMENTS The authors would like to express their gratitude to the Greek Shipping community for providing valuable feedback over the years. 8. REFERENCES 1. TELFER E. V., ‘Merchant Ship Service Performance Analysis’, Institute of Marine Engineers, 12 March 1929. 2. ITTC Recommended Procedures and Guidelines, Testing and Extrapolation Methods, Propulsion, Cavitation, Model – Scale Cavitation Test, 7.5–02, 03-03.1 3. SZANTYR J.A.. ‘Scale effects in cavitation experiments with marine propeller models’, Polish Maritime Research, No 4/2006. 4. TOWNSIN R.L., BYRNE D., SVENSEN T.E. and MILNE A., ‘Estimating the Technical and Economic Penalties of Hull and Propeller Roughness’, Trans. SNAME, Vol. 89, 1981. 5. API Standards, Manual of Petroleum Measurement Standards (MPMS), Chapter 2.8A Calibration of Tanks on Ships and Oceangoing Barges and Chapter 2.8B Recommended Practice for the Establishment of the Location of the Reference Gauge Point and the Gauge Height of Tanks on Marine Tank Vessels. 6. KIDA T. and HARADA T., ‘Characteristic of Main Engine Specific Fuel Oil Consumption on Sea Trial’, Proceedings of the 7th International Symposium on Marine Engineering, Tokyo, 24- 28 October 2005. 7. STAIMO software for the analysis of speed/power trials both for contract delivery trials and for EEDI trials, www.staimo.org 8. CAIROLI C. et al., ‘Optimization for Minimum Propulsive Power: Model Scale versus Full Scale’, RINA conference Energy Efficient Ships, London, 23-24 November 2016. 9. AUTHORS BIOGRAPHY Lefteris Karaminas holds the current position of Divisional Manager of Europe Learning Center at ABS. He has responsibility for staff and client training courses in the Division. In particular, he has been developing and providing relevant learning sessions and guidance to Owners. Lefteris is a Fellow of RINA, Chartered Engineer and a scholar on ship performance since the 80’s, carrying out studies and software development on resistance and propulsion aspects, including propeller
- 11. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects design & cavitation, model testing, seakeeping, powering prediction, performance and benchmarking. His previous experience includes: Navy, tanker and bulk carrier repairs and operations, marine software house, yacht surveys, R&D and marine business development at Lloyd’s Register, ship-management, newbuildings projects and consultancy. Tao Shen holds the current position of Senior Engineer of Operational & Environmental Performance Center at ABS. He has responsibility for concept ship design optimization and evaluation and the development of innovative solutions for enhanced operational and environmental performance. In particular, he has been developing and delivering the hull performance training course to client. Tao is an Associate Member of RINA. His previous experience includes: ship design, hull form development, speed-power prediction, model test participating. 10. DISCLAIMER The views and opinions expressed in this article are those of the authors and do not necessarily reflect the position or views of American Bureau of Shipping.
- 12. Energy Efficient Ships, 23-24 November 2016, London, UK © 2016: The Royal Institution of Naval Architects