Material has always been a key element in shipbuilding. The most widely used
material is steel. However, the commonly used ordinary steel plates are usually
much thicker than high strength steel plates and play a significant part in
the total ship weight. Reducing empty ship weight will lead to a reduction in
fuel consumption. This paper evaluates the use of high strength steel plates
instead of normal steel plates to reduce material thickness. Due to increasing
consumption of non-renewable energy like petroleum and the urgency to improve
the ecological environment, energy conservation has become an important business
consideration globally. LPG/CNG/LNG are considered as Green fuel.
Compared with an ordinary fuel engine (petrol and diesel), gas fuelled engines
reduce: Carbon Oxide (CO) emissions 70~90%, HC emissions 30~40%, NOX emissions
20~40%, CO2 emissions 20% and Particulate Matter (PM) more than 95%.
This technology has already been applied on car engines successfully and is
widely used all around the world. Similar systems can also be installed on vessels;
Dual Fuelled Diesel Engines (DFD engine) are one of the most suitable devices.
In this study, DFD engines are proposed (Ehsan and Bhuiyan,
2010). Solar power and wind energy are proposed as the most attractive renewable
energy sources for ships. However, low energy density and storage difficulties
make it hard to use these two energy sources as the main fuel on ships but rather
they are proposed as adjunct sources of power.
By using material having mechanical properties greater than those of ordinary
strength hull structural steel, the minimum hull girder section modulus required
can be reduced significantly therefore reducing plates thickness in certain
positions is possible to accomplish. The following contents are detail calculations
for the parts of plates that need to be optimized. The minimum required hull
girder section modulus, SM, at amidships is given by Eq. 1
||Amidships coefficient and equal to 0.0451 L+3.65 61 = L<90
||Length coefficient 0.01
||The length of vessel, in m (ft)
||The breadth of vessel, in m (ft)
||The block coefficient at design draft, based on the length, L, measured
on the design load waterline. Cb is not to be taken as less than
When either the top or the bottom flange of the hull girder or both, is constructed
of higher-strength material, the section modulus may be reduced by the factor
Q, as in Eq. 2 (ABS, 2005):
where, SMhts is minimum required hull girder section modulus with high strength material.
In this study, H47 steel is selected as high strength material so Q value corresponds to 0.62 for all situations as shown in Table 1. Three positions of the ship are optimized which include: shell plating, deck plating and bottom structure.
Bottom shell plating: The term bottom plating refers to
the plating from the keel to the upper turn of the bilge or upper chine. The
thickness of the bottom shell plating throughout is not to be less than that
obtained from Eq. 3 (ABS, 2005):
||Thickness of bottom shell plating, in mm (in)
||Frame spacing, in mm (in)
||Depth, D, in m (ft), but not less than 0.1 L or 1.18 day whichever is
When using higher-strength material and where longitudinally framed, it is
to be not less in thickness than that obtained from the following equation (ABS,
|| Material factor and strength (ABS, 2005)
||The thickness of higher-strength material, in mm (in)
||The thickness, in mm (in), of ordinary-strength steel, as required by
preceding paragraphs of this section, or from the requirements of other
sections of the rules, appropriate to the vessel type
||The thickness coefficient equal to 4.3 mm
||As defined above
Side shell plating: The term side plating refers to the plating hold frames of dry cargo vessels and located at the side position of vessel. The side shell plating is not to be less in thickness than that obtained from:
where, t, s and h are defined as above.
Side-shell plating, where constructed of higher-strength material, is to be not less in thickness than that obtained from:
where, thts and tms as defined above.
All deck: In general, applications of higher strength materials are
to take into consideration the side suitable extension of the higher strength
material below the deck, forward and aft. Care is to be taken to avoid the adoption
of reduced thickness of material such as might be subject to damage during normal
operation. The thickness of the deck plating for longitudinally framed decks,
where constructed of higher strength material, is to be not less than required
for longitudinal strength, nor is it to be less than that obtained from Eq.
3 (ABS, 2005). With high strength material use Eq.
Center girders: The vessel considered in this work is defined as Single
Bottoms with Floors and Girders. Single-bottom vessels are to have center keelsons
formed of continuous or intercostal center girder plates with horizontal top
plates. The thickness of the keelson and the area of the horizontal top plate
are to be not less than that obtained from the following equations. The girders
are to extend afar forward and aft as practicable (ABS, 2005).
Center-Girder Plate Thickness Amidships is given by:
||Thickness of center-girder plate, in mm (in)
||Length of vessel, in m (ft)
With high strength material use Eq. 6.
|| Empty ship weight comparison (ABS, 2005)
Side girders: Side girders are to be arranged so that they are not more
than 2.13 m (7 ft) from the center girder to the inner side girder, from girder
to girder and from the outer girder to the lower turn of bilge. Forward of the
amidships one-half length; the spacing of girder on the flat of floor is not
to exceed 915 mm (36 in.). Side girders are to be formed of continuous rider
plates on top of the floors. They are to be connected to the shell plating by
intercostal plates. The intercostal plates are to be attached to the floor plates.
In the engine space, the intercostal plates are to be of not less thickness
than the center girder plates (ABS, 2005). The scantlings
of the side keelsons are to be obtained as Side Girder and Intercostal Thickness
With high strength material use Eq. 6:
Floors: The minimum thickness of floors is not to be less than that
obtained from the following Eq. 9 (ABS,
where, hf is the floor depth in mm (ft).
With high strength material use Eq. 6. The model used in the approach came from Shanghai ML Marine Design Co., Ltd. which is one 86.01x21.36x5.20 m Deck Cargo Barge. This model is a non-propeller, single bottom, nobody on barge. Expect from the optimized position, all the other dimensions for the sample vessel came from original design draft; this approach keeps the original material and structure data for the rest position of the vessel for calculating total ship weight. By using the above equations, the empty ship weight prior to optimization and after optimization is shown in Table 2. Eleven percent reduction is achieved from the original design (i.e., design prior to optimization).
DUAL FUEL DIESEL ENGINE
A Dual Fuel diesel engine is usually built from an ordinary diesel engine.
Builders will fit it with additional devices allowing it to utilize natural
gas as a supplemental fuel. This engine type is a true diesel engine and requires
some level of diesel to ignite the gas fuel. This engine type has been available
to industry since the 1930s. Its use was almost exclusive to power generation
where the fuel supply was a pipeline source. Its availability was almost exclusively
through the Original Equipment Manufacturer (OEM) (Brett,
The dual fuel engine type has a number of quality attributes. A primary benefit
is that of fuel flexibility, operating with cleaner cheaper natural gas when
available and on diesel alone when necessary. Many hundreds of these engines
were employed in the US during the rural electrification period (Reddy
et al., 2008). After grid power became economical, many of these
engines were discarded. With uncertainties in power availability, emissions
and the current price of diesel, dual fuel engines are gaining a new popularity
A single cylinder diesel engine (Model S1100DONGFENG, China) widely used in
Bangladesh was chosen for this study.
|| Air-fuel ratio (AFR) in dual operation (Bhuiyan et al.,
The engine was designed to operate in a narrow speed range (about 1800-2200
rpm), with a rated speed of 2200 rev/min. The engine was tested at constant
rated speed throughout its power range with diesel-only and dual fuel operations
using a standard hydraulic (water-brake) dynamometer (TFL-109, Germany) and
the test results were de-rated to standard conditions according to BS5514 (Ehsan
and Bhuiyan, 2010).
In Table 3, the attached specification of the engine shows
a maximum rated power of 15 metric horsepower (PS) at 2200 rpm, in real testing
however, the maximum power was found to be limited to about 13 hp when running
on diesel. Later the engine was tested at 10, 30, 50, 75, 90 and 100% of the
actual rated load, at a constant rated speed of 2200 rpm in dual fuel mode.
For each setting, diesel was used as the pilot fuel for starting auto ignition
while natural gas from line supply was used as the main fuel. For each power
level the proportion of natural gas replacing diesel was gradually increased
by manually opening a control valve to determine the maximum possible diesel
replacement using natural gas with satisfactory engine performance. The overall
accuracy of Brake Power and Brake Specific Fuel Consumption rates are expected
to be within ±2% error band (Ehsan and Bhuiyan, 2010).
As showed in Fig. 1 and 2 natural gas has
a different Air-fuel Ratio (AFR) in dual operation. AF ratio decreases sharply
with increased load, as the fuel flow (diesel-only or dual) increases while
the air flow decreases slightly.
On the other hand, natural gas has a higher requirement of air for stoichiometric
combustion (17.2 by mass) compared to diesel (14.6 by mass). As a result of
a high rate of diesel replacement with natural gas the engine is restricted
in terms of maximum power produced. For loadings of 10, 30, 50 and 75% of the
actual rated load the engine could produce the required power with up to 90%
diesel replacement. At 90% load up to 88% replacement was possible but at full
load this was restricted to 69% diesel replacement only (Ehsan
and Bhuiyan, 2010).
Figure 3 and 4 show the variation of CO2
and CO emission from the engine with increased diesel replacement of natural
gas at different power levels. Exhaust analyzer measurements showed that generally,
the volume of CO (less than 0.1%) formed and the proportion of CO2
(2-5%) in the exhaust gas was very low which is typical of a diesel engine.
With higher diesel replacement the level of CO2 generation decreased
and CO emission was found to increase (Brett, 2008).
The late burning of the mixture with higher diesel replacement levels of natural
gas had caused more fuel to remain partially unburned increasing the formation
of carbon monoxide and decreasing the proportion of Carbon-dioxide. This would
contribute to the reduction of efficiency at light loads (Ehsan
and Bhuiyan, 2010).
SOLAR AND WIND ENERGY
Photovoltaic (PV) system as a support power supply system for lighting on
vessels: Recently, solar powered cars and aircrafts are generating more
research and development. Compared with cars and planes, ships have a much larger
dimension, thus they have more surface area from which to generate solar power.
The low travelling speed of ships make it convenient to have solar power devices
on board, also these devices would have little effect on the total ship weight
and stability. Other factors (like deck and upper hatch cover insulation) can
be considered at the same time (Yasin et al., 2011).
Ferries usually have flat and wide tops and comparatively small hull structures.
According to recent solar power technology, ferries should be considered first
as a trial (Thwaites, 2006). Other types of vessels (tugboat,
container ship, bulk cargo vessel, etc.) have less deck space. The only space
that can be used to install solar panels is at the top of the deckhouse and
on different balusters (which have limited space). However, these kinds of ships
have few passengers on board (mainly sailors), so installing solar panels for
bath or heating during winter time is a rewarding choice to reduce fuel consumption
(Yasin et al., 2011).
As shown in Table 4, for both reliability and quality factors,
using PV system on vessel is similar as using diesel fuelled generator. And
at the diesel price of 7 Yuan kg-1, both plans will cost same amount
of money in 20 years operation. However, the price of diesel is more than 10
Yuan kg-1 recently, therefore, using PV system may cost less (Al-Hadidi
and Ibrahim, 2008).
Sail usage on vessels: According to sails character, the vessels for
sail installation should have high stability and plenty of deck space. Usually,
bulk cargo carrier and crude oil tankers are the most suitable types. Bulk cargo
carriers, with flat and wide decks, make it easy to arrange the location of
sails. Depending on modern sail-making technology and the ships travelling condition,
cyclometer sails with rigidity frame is most suitable for this type of vessel
|| System power supply versus diesel fuelled generator supply
For vessel at certain velocity, when it is influenced by certain direction
and velocity wind, energy ΔPS gain from the wind can be expresses in Eq.
||The velocity wind apply on sail
||The force apply on sail
||The resistance of water
||The resistance caused by rudder operation
||it the push efficiency
Force on sail XWF use Eq. 11 and 12:
||The maximum push coefficient
|| Angle between ship stem center line and wind direction
||The area of sail
||The lift coefficient
||The drag coefficient
Velocity of wind Vs is obtained from Eq. 13 and 14:
Because usually β is very small, Eq. 13 can be simplified as:
Drag force caused by rudder operation XR is expressed in Eq. 15:
||The rudder area
||The flow rate
||The rudder length versus width rate
||The Surge rate
||The rudder angle
From the computation, ΔPS = 5.77x105 kWh was obtained; while the main engines fuel consumption rate is around 178 g/kWh+5%, the vessel average velocity is 12 knot. By using the estimating software we can easily get total fuel saving of 102.7 ton; the sail produces 0.229 kWh energy per square meter. During the voyage, 3.4 ton fuel can be saved every day due to the use of sails. According to the annual wind frequency, the annual fuel saving can reach 1060.8 ton. With higher vessel velocity more wind energy will be applied by sail, by using different coefficient for the different types of vessel, the sail area needed can be obtained.
For the minimizing of empty ship weight case, 11% reduction of empty ship weight was achieved from the original design. DFD engines exhaust analyzer measurements showed that generally, the volume of CO (less than 0.1%) formed and the proportion of CO2 (2-5%) in the exhaust gas was very low. By using sailor on vessels 3.4 ton fuel can be saved every day, the annual fuel saving can reach 1060.8 ton.
CO2 emissions from global shipping amounts to 10% of total transport
CO2 emissions worldwide.(Nwaichi and Uzazobona,
2011) This result alerts the shipping industry of the urgency of building
environmentally friendly ships. In the process to minimizing the ship weight
presented in this paper, we reduced the total ship weight by 11% and the CO
and CO2 emissions of DFD engines are considerably lower than diesel
engine. Finally, the usage of solar and wind energy will contribute to saving
significant amounts of fuel every year. Future areas of research include risk
analysis, safety factors and refueling issues.
The authors acknowledge School of Advanced Manufacturing and Mechanical Engineering, University of South Australia for technically supporting.