4200 cubic meter lng bunkering vessel concept design · 2021. 1. 5. · dr. james a. lisnyk student...

DR. JAMES A. LISNYK

STUDENT SHIP DESIGN COMPETITION 2020

4200 CUBIC METER LNG BUNKERING VESSEL

CONCEPT DESIGN

ALEXANDER BIDWELL, OSCAR COMO, LUKE HERBERMANN, & BENJAMIN HUNT

WEBB INSTITUTE CLASS OF 2021

i Dr. James A. Lisnyk Student Ship Design Competition

TABLE OF CONTENTS

LIST OF TABLES ........................................................................................................................ III

LIST OF FIGURES ...................................................................................................................... IV

STUDENT CERTIFICATION ...................................................................................................... V

ACKNOWLEDGEMENTS .......................................................................................................... VI

DESIGN REQUIREMENTS .......................................................................................................... 1

REPORT SUMMARY & TABLE OF PRINCIPAL CHARACTERISTICS ................................ 2

CONCEPT SELECTION AND INITIAL DEFINITION............................................................... 3

HULL FORM DEVELOPMENT ................................................................................................... 9

SECTIONAL AREA CURVE ........................................................................................................ 9

LINES PLAN ................................................................................................................................ 10

CURVES OF FORM .................................................................................................................... 10

SPEED AND POWER ESTIMATE ............................................................................................. 10

GENERAL ARRANGEMENT .................................................................................................... 11

AREA VOLUME REPORT ......................................................................................................... 15

CAPACITY PLAN ....................................................................................................................... 15

STRUCTURAL DESIGN ............................................................................................................. 15

PROPULSION PLANT TRADE-OFF STUDY ........................................................................... 22

MACHINERY ARRANGEMENT ............................................................................................... 28

H, M, AND E SYSTEMS AND EQUIPMENT ........................................................................... 29

CARGO TRANSFER SYSTEM .................................................................................................. 33

ELECTRICAL SYSTEM ............................................................................................................. 48

ENDURANCE CALCULATION ................................................................................................ 51

WEIGHT ESTIMATE .................................................................................................................. 53

STABILITY .................................................................................................................................. 57

SEAKEEPING ANALYSIS ......................................................................................................... 59

MANNING ESTIMATE .............................................................................................................. 60

COST ANALYSIS........................................................................................................................ 61

DESIGN COMPLIANCE MATRIX ............................................................................................ 63

RISK ASSESSMENT AND SUGGESTIONS FOR FUTURE WORK ...................................... 63

REFERENCES ............................................................................................................................. 65

: FINAL DESIGN REQUIREMENTS .............................................................. A-1

ii Dr. James A. Lisnyk Student Ship Design Competition

: ROUTE ANALYSIS ........................................................................................ B-1

: LINES PLAN ................................................................................................... C-1

: CURVES OF FORM........................................................................................ D-1

: GENERAL ARRANGEMENT ......................................................................... E-1

: AREA AND VOLUME REPORT .................................................................... F-1

: CAPACITY PLAN .......................................................................................... G-1

: STRUCTURAL MIDSHIP SECTION ............................................................ H-1

: STRUCTURAL CALCULATIONS ................................................................... I-1

: MACHINERY ARRANGEMENT .................................................................... J-1

: CARGO TRANSFER SYSTEM DRAWINGS ............................................... K-1

: FLOW CALCULATIONS ................................................................................ L-1

: ABS PIPE WALL THICKNESS CALCULATIONS .................................... M-1

: ELECTRICAL SYSTEM CALCULATIONS ................................................. N-1

: ENDURANCE CALCULATIONS ................................................................. O-1

: WEIGHT ESTIMATE ....................................................................................... P-1

: STABILTIY CALCULATIONS ..................................................................... Q-1

: FLOODABLE LENGTH CURVES ................................................................ R-1

: SEAKEEPING CALCULATIONS ................................................................... S-1

iii Dr. James A. Lisnyk Student Ship Design Competition

LIST OF TABLES

Table 1. Principal Particulars .......................................................................................................... 3 Table 2. Excel Model Example ....................................................................................................... 6 Table 3. Initial Parametric Analysis Results ................................................................................... 9 Table 4. Designed and Required Section Modulus and Moment of Inertia .................................. 22

Table 5. Fuel Type Pros and Cons ................................................................................................ 24 Table 6. Drive Type Pros and Cons .............................................................................................. 25 Table 7. Propulsor Type Pros and Cons........................................................................................ 27 Table 8. Wärtsilä Generator Configuration .................................................................................. 28 Table 9. Mission Specific Equipment ........................................................................................... 33

Table 10. Summary of Flowrates and Heads of Governing Cases ............................................... 38 Table 11. Pipe Characteristics....................................................................................................... 42

Table 12. EPLA Results ................................................................................................................ 48 Table 13. Wärtsilä 6L20DF Specific Fuel Consumption.............................................................. 51 Table 14. Wärtsilä 8L34DF Specific Fuel Consumption.............................................................. 51 Table 15. Design Transit Fuel Consumption ................................................................................ 52

Table 16. Daily Fuel Consumption ............................................................................................... 52 Table 17. Voyage Fuel Consumption ........................................................................................... 53

Table 18. Weights and Centers Estimate Summary...................................................................... 53 Table 19. General Operability Limiting Criteria for Ships (NORDFORSK, 1987) ..................... 59 Table 20. Manning Estimate ......................................................................................................... 61

Table 21. Cost Estimate ................................................................................................................ 62 Table 22. Design Compliance Matrix ........................................................................................... 63

iv Dr. James A. Lisnyk Student Ship Design Competition

LIST OF FIGURES

Figure 1. Route Analysis Solution .................................................................................................. 4 Figure 2. Generated Plot Example .................................................................................................. 7 Figure 3. Calculations Sheet Example ............................................................................................ 8 Figure 4. Sectional Area Curve ..................................................................................................... 10

Figure 5. Orca3D Holtrop Analysis Results ................................................................................. 11 Figure 6 KHOBRA Transfer System ............................................................................................ 13 Figure 7. KLAW LNG Transfer System....................................................................................... 13 Figure 8. Fender Davit .................................................................................................................. 14 Figure 9: Longitudinal Weight Curve ........................................................................................... 18

Figure 10. Buoyancy Curve .......................................................................................................... 18 Figure 11: Longitudinal Net Load Curve...................................................................................... 19

Figure 12: Shear Force and Bending Moment Diagram ............................................................... 20 Figure 13. ABS Hogging and Sagging Moment calculation ........................................................ 20 Figure 14. ABS Wave Induced Bending Moment Distribution Factor ........................................ 21 Figure 15. System Head Curve for Cargo Pumps ......................................................................... 39

Figure 16. System Head Curve for LD Compressors ................................................................... 40 Figure 17. System Head Curve for HD Compressors ................................................................... 40

Figure 18. System Head Curve for Stripping Pump ..................................................................... 41 Figure 19. System Head Curve for Fuel Supply Pump ................................................................. 41 Figure 20. Bunker Operation Sensitivity ...................................................................................... 44

Figure 21. Loading Operation Sensitivity ..................................................................................... 45 Figure 22. Fuel Supply Sensitivity................................................................................................ 45

Figure 23. Spray Down Sensitivity ............................................................................................... 46

Figure 24. Location of Down flooding Points .............................................................................. 58

v Dr. James A. Lisnyk Student Ship Design Competition

STUDENT CERTIFICATION

This is to certify that the following members were part of the design team and by this statement, I

certify that the work done for this design competition was completed by the student team members.

Student Name Signature

Alexander Bidwell

Oscar Como

Luke Herbermann

Benjamin Hunt

Professor Bradley Golden

Faculty Advisor

vi Dr. James A. Lisnyk Student Ship Design Competition

ACKNOWLEDGEMENTS

We would like to thank the following individuals for their invaluable support and guidance on this

project.

- Professor Bradley Golden – Webb Institute

- Ethan Wiseman – NYC EDC

- Tom Sullivan – Northstar Midstream

- Raymond Gagliardi – Excelerate Energy

- Peter Wallace – Sea One Caribbean

- Professor Ben Scott – Webb Institute

- Professor Michael Martin – Webb Institute

- Professor Adrian Onas – Webb Institute

1 Dr. James A. Lisnyk Student Ship Design Competition

DESIGN REQUIREMENTS

INTRODUCTION

This section outlines the design requirements specified by the client in full detail. The

requirements were given to the team on February 24th, 2020 and have been revised 3 times. We

will summarize the major changes in the following section. The final design requirements can be

found in Appendix A.

DESIGN REQUIREMENT CHANGES

Increasing Maximum LOA

The maximum LOA for our vessel was extended from 90.0m to 95.0m. We conducted an

analysis of the cargo capacity needed to supply gas for our dual-fuel engine and bunker LNG to

the cruise ships. Our vessel did not have enough capacity to complete both missions at 90.0m, so

we asked for an extension to our maximum LOA. This allowed our vessel to employ duel-fueled

engine, which lead to cost savings and decreased emissions.

Lower Maximum Speed Requirements

The maximum speed requirement was lowered from 18 knots to 16 knots. This reduction

in speed decreased the installed power on our vessel by over half, allowing for a more optimal

powering arrangement. We conducted a route analysis to prove that the new maximum speed still

had a sufficient time margin to handle weather delays with delaying bunkering of the cruise ships.

Specifically, we increased the distance between ports by 50% to simulate a reroute or delay for

weather. This calculation can be found in Appendix B.

Modify Pump Requirements

The individual flowrate requirement for the cargo pumps was lowered from 600 cuM/hr to

500 cuM/hr and the maximum discharge pressure be raised from 4.5 bar to 7 bar. This was driven

by an in-depth design of the cargo transfer system we carried out. These changes allowed us to

optimize the cost of our systems well still meeting the goals of our client. The raise in the maximum

discharge pressure allowed to select the optimal pipe diameter to reduce the overall cost of the

system. The lowering of the individual cargo pump capacity allowed us to select a pump that will

be at maximum efficiency at our design flowrate of 500 cuM/hr. We provide redundancy in our


system by selecting removable pumps, that can be quickly exchanged should one break, instead of

oversizing the individual pump capacity.

REPORT SUMMARY & TABLE OF PRINCIPAL CHARACTERISTICS

The concept design for the LNG Bunkering Vessel was completed on May 30th, 2020. This

concept design represents one “loop” through the design spiral. Several aspects of the design

should be further refined in order to have a comprehensive design package that is ready for

manufacture.

At the beginning of the design process the team analyzed the design requirements and

potential routes of the vessel. This was followed by a parametric analysis of the world fleet of

LNG bunkering vessels. Using this data, we came up with the principal particulars. The next step

was to create a hull form and a preliminary general arrangement. A weight estimate had also been

started at this stage to contribute to the stability and hydrostatic calculations. After this point in the

design, we made a conceptual midship section to prove our ship’s structural integrity. Then, the

design the team selected propulsion method the propulsion plant and associated machinery. This

was followed by a stability analysis on the final concept design. Finally, a basic cost estimate was

procured on the design and construction of the vessel. A broad idea of the vessel is conveyed in

the following table of principal characteristics. Some the final concept characteristics do not

comply with the initial design requirements. This likely means that somewhere in the design

process the requirement was found to be infeasible. All infeasible requirements were discussed

with the client and changed to better suit the vessel limitations.


Table 1. Principal Particulars

CONCEPT SELECTION AND INITIAL DEFINITION

The design process for the LNG bunkering vessel began with a route analysis to better

define how the ship would service the cruise ships in Miami and San Juan. The following

paragraphs elaborate on the route analysis.

ROUTE ANALYSIS

We carried out a simple analysis to determine what routes would allow two ships to fulfill

the bunkering schedule specified by the owner. The owner’s bunker requirements are to bunker

1,500 cuM of LNG every seven days to two separate cruise ships. One cruise ship is to be bunkered

in Miami, FL and the other cruise ship is to be bunkered in San Juan, PR. The bunker vessel will

load LNG at a shoreside terminal located in Jacksonville, FL.

We established an accurate estimate of the bunker and loadings operation timelines using

information from our mentor, Tom Sullivan, as well as a mix of research and our group’s

knowledge of Ship-To-Ship (STS) LNG transfer operations. We determined our vessel would

require 7 hours to complete the 1500 cuM bunkering operation utilizing a transfer rate of 1000

cuM/hr. The loading operation at the Jacksonville LNG Terminal is estimated to take 13 hours

utilizing the terminal’s design transfer rate of 2400 gpm. Route analysis calculations include

estimated connection and disconnection time as well as time for liquid-freeing and purging

operations.


At first glance it was clear that one vessel would not satisfy the mission because the route

was far too long to complete in one week at a service speed of 14 knots. We considered utilizing

a fleet of two vessels, each dedicated to serving a single port. This was determined to be infeasible

because the route from Jacksonville to San Juan was too far long to service every week with one

vessel. Next, we considered using two vessels operating in a loop between Jacksonville, San Juan

and Miami. It was determined that the bunkering schedule could be met if the two vessels operate

on staggered schedules. The calculation tables for this analysis can be found in Appendix B.

Figure 1. Route Analysis Solution

PARAMETRIC ANALYSIS

After the route analysis, the design team started gathering characteristic data of the world

fleet of LNG bunkering vessels. The key characteristics we gathered were:

• Length overall

• Beam

• Draft

• Depth

• Cargo capacity

• Speed


Prediction Path

The driving factor of the parametric analysis was cargo capacity as it is integral to the

vessel’s mission. The vessel must have a cargo capacity of around 4000cuM to sufficiently supply

the two cruise ships. This estimated cargo capacity was the used as a starting point for our

parametric analysis

We found tank capacities for every LNG bunkering vessel we researched, providing a good

basis for our parametric analysis. With this data, we interpolated at 4000cuM to find the length

overall of our ship. Using this length, we interpolated for other parameters such as beam, depth,

design draft, main engine MCR, and gross tonnage.

We increased the overall size of the vessel based on advice from our advisors and our

technical knowledge. This eases the process of making a general arrangement and prevents having

to increase the size of a ship later in the design process. Increasing the size later in the design

process can cause the vessel to have to comply with new regulations for its larger size. Having to

adjust a pre-existing design to meet new requirements is tougher than to deal with them in the

beginning design stages.

Analytic Approach

We conducted a parametric analysis to select a starting point for our LNG bunkering

vessel’s principal particulars. These particulars include the length, beam, depth, and draft of the

vessel. Essentially, the parametric analysis creates a visual representation of the numerical

similarities and differences between currently operational vessels that share similar mission

statements.

For our case, we gathered values for various parameters from several LNG vessels with

relatively similar cargo capacities. Due to the infant nature of the LNG bunkering industry, there

is a lack of available public information on these vessels. Much of the detailed information on

current LNG bunkering vessels remains non-public due to proprietary nature of the designs. With

a database populated with sufficient values for most of the parameters, we were able to begin

analyzing all our data entries.

For the analysis, we developed a Microsoft Excel model. The model is made up of three

different sheets. The “Combined” sheet is the combined data from all the ships researched by each


individual group member. The “Interface” sheet contains the input and output of the model, and

the “Calculations” sheet shows the derivations and steps to arrive at the output displayed on the

interface sheet. We developed and used this model to reduce the total amount of work done by

hand in Microsoft Excel.

There are four inputs required to generate a plot. The inputs are drop down boxes describing

which parameter the user would like to predict (Y axis) and the parameter the user would like to

base that prediction off of (X axis). The user can choose a linear, logarithmic, or natural

logarithmic scale for each parameter selected. With these four inputs entered, a plot is generated

on the same sheet to the right of the model table. For the Prediction Calculator portion of the

model, the user inputs a desired value of the independent variable that matches the X parameter in

the same row under the Plot Generator Inputs table. The output column calculates and displays the

predicted dependent variable value using the selected regression equation based on the scaling

factor chosen under the Plot Generator Inputs table. Adjacent to the output value is the calculated

r2 value for the corresponding plot generated. The r2 value, or coefficient of determination, is the

proportion of the data explained by the generated linear regression model, and it gives us a

numerical evaluation of our predicted value. A higher r2 value (values range from 0 to 1) indicates

a better fit. An example is shown below in Table 2. Figure 2 shows the corresponding plot

generated.

Table 2. Excel Model Example


Figure 2. Generated Plot Example

Contained within the Calculations sheet are the groups of individual entry calculations and

generated plots. These groups are broken up into bordered off sections that are clearly identified

and labeled. An example of one calculation section can be seen below in Figure 3.

The left side of Figure 3 depicts each vessel’s respective parameter values extracted from

the combined data sheet. With these values, we created a scatter plot. We also used the slope,

intercept, and r2 Excel functions to create a linear regression equation. With this information as

well as the desired scaling of each parameter of interest, we were able to predict a Y value for a

given X value. The top right portion of Figure 3 shows the adjustment calculation for scaling when

using a logarithmic or natural logarithmic scale. The example shown uses linear scaling on both

axes, so there is no adjustment made.


Figure 3. Calculations Sheet Example

The only nuances we noticed with this model were the problems that came from the

incompleteness of the data sheet. For each pair of entries per vessel, if there is a vessel with one

or no values, the user must manually clear the entries within the calculations sheet in order for the

data to be plotted correctly. Additionally, for each plot created over an existing user entry in the

model table, the user needs to manually drag and autofill the top row of the extracted values from

the data sheet. This populates the formally deleted rows with their newly extracted values taken

from the combined data sheet.

Analysis Result

Tabulated below in Table 3 are the results of our parametric analysis. We purposely

increased all of the predicted values in choosing the vessel’s principle particulars. We did this

because it is significantly easier to decrease these values versus increasing them further along in

the design process. Information regarding the order and methodology in which these values were

decided on has already been covered under the section titled, “Prediction Path”.


Table 3. Initial Parametric Analysis Results

After these estimates were made, the actual designing of the ship caused some of these

parameters to diverge from the initial parametric analysis. For example, in the next section about

the hull form development, the initial hydrostatics report proved that our design draft would be

rather difficult to meet. In actuality, the design draft would fall around 3.75 m instead of 5.1 m.

We also increased our cargo capacity and length overall all to accommodate duel fuel engines.

HULL FORM DEVELOPMENT

We used the Orca 3D Hull Assistant to create a hull form for our LNG bunkering vessel.

We picked the “ship assistant” design from the library of hull designs. Using the results from our

parametric analysis, we created a hull form with our particulars of 90 m LOA, 20 m beam, and 10

m depth. The hull form was heavily inspired by the existing designs such as GTT’s 90m bunker

vessel concept design. In our final design, there is an extra 2.9 meters added to the LOA because

of our forecastle deck. In one of the following sections we discuss making the general arrangement.

While we were making the general arrangement, the cargo tanks were designed to comply with

the International Gas Carrier code (IGC code). Since this turned out to be a challenge, the design

team spoke with the client and discussed increasing the length overall. This did not impact our hull

form; however, it allowed us to add a forecastle deck without worrying about our ship having

trouble complying with the IGC code while meeting our needed cargo capacity.

SECTIONAL AREA CURVE

Orca 3D hydrostatic report to generate the section areas for the sectional area curve at the

design draft of 3.75 m. The data was then plotted in Excel to produce sectional area curve shown

below in Figure 4.

Parameter Model Results Finalized Parameter

Length (m) 93.9 90

Cargo Tank Capacity (m^3) N/A 4000

Beam (m) 17.1 20

Design Draft (m) 5.1 5.5

Depth (m) 7.8 10

Main Engine MCR (kW) 2376.1 3500

ITC Gross Tonnage 4958.7 5000


Figure 4. Sectional Area Curve

LINES PLAN

The lines plan was created using an export of intersecting planes with the hull form in

Rhino. Because the propeller shaft gondolas were instituted rather late in the design, they do not

appear on the lines plan. The buttock lines and waterlines are taken every two meters along the

respective direction and the stations are spaced every 9.0 m. For the lines plan drawing, see

Appendix C.

CURVES OF FORM

The curves of form for a vessel represent its hydrostatics at the indicated loading conditions

and draft lines. These curves of forms can be found in Appendix D.

SPEED AND POWER ESTIMATE

The bare hull resistance and propulsion powering requirement was determined by

performing a Holtrop analysis in Orca3D. Propulsive efficiencies for the B-series of propellers

were utilized in the analysis to determine the required propulsion plant power. At 16kts, the total

bare hull resistance was determined to be 497 kN and the required power was determined to be


8000 kW. For the design transit speed of 14kts, the bare hull resistance is 277 kN and the required

propulsive power is 3900 kW. The results of the Holtrop analysis are shown below in Figure 5.

Figure 5. Orca3D Holtrop Analysis Results

GENERAL ARRANGEMENT

The general arrangement for our vessel is laid out in Appendix E. This arrangement

contains the outboard profile, inboard profile, weather deck plan view, main deck plan view,

machinery arrangements, accommodation space arrangements, and a midship section view. The

layout of the spaces and arrangement of the machinery allows the vessel to efficiently fulfill the

Owner’s Requirements while complying with applicable regulatory codes.

Cargo Containment

Two spherical ended Type C independent tanks are utilized for cargo containment. This

containment system offers several distinct advantages over membrane containment systems. Type

C tanks have a higher durability and are less expensive than their counterparts. These tanks can

withstand pressure stemming from excess boil-off gas, providing an added level of resiliency in

the realm of cargo management. The placement of the cargo tanks is fundamental aspect of the

design and influences the arrangement of the cargo transfer and cargo management systems. The

arrangement of the tanks relative to the hull structure was ultimately dictated by IGC code 2.5.1,

which defines the minimum distance between the cargo containment system and the hull. This


placement heavily influenced the arrangement of the cargo systems and deck machinery as well as

the physical layout of the piping on deck.

Weather Deck

The vessel features two cargo manifolds, port and starboard, located at midships. The

decision to place the manifolds at midships was influenced by the manifold orientation on similar

LNG bunkering vessels. The height and transverse position of the manifolds was set to allow for

compatibility with the transfer arms of the shoreside terminal. Each manifold consists of a single

liquid line and two vapor lines, as specified in the Owner’s Requirements. Each manifold features

a deluge system to comply with both the Owner’s Requirements and regulatory standards. During

cargo operations, this system blankets the surrounding ship structure with a protective layer of

water. This system maintains the integrity of the surrounding structure in the case of a loss of

containment.

Two knuckle boom hose handling cranes are located forward of each cargo manifold.

These cranes allow for efficient deployment of hoses and transfer equipment during ship-to-ship

(STS) operations. We identified two potential LNG STS transfer systems suitable for use onboard

this vessel. The KHOBRA system, produced by Houlder LNG Technology and Solutions,

integrates the liquid hose, vapor hose, and the emergency release coupling (ERC) into a single,

compact package. The streamlined nature of this design would simplify bunkering operations and

decrease bunkering time. Another potential candidate is transfer system offered by KLAW LNG.

This saddle and hose system is proven and has been utilized in countless LNG STS operations

around the globe. Depictions of the two systems are shown in Figure 6 and Figure 7 respectively.


Figure 6 KHOBRA Transfer System

Source: houlderlng.com

Figure 7. KLAW LNG Transfer System

Source: klawlng.com


The compressor room is located on the aft portion of the weather deck due to the integral

role of the compressors in cargo management and cargo transfer operations. This location

simplifies the piping arrangement and is compliant with the standards outlined in the IGC code,

which states that cargo transfer lines must not pass though or underneath accommodation spaces.

Mooring

The vessel features two forward double wildcat anchor windlasses and two aft winches

for mooring operations. Four davit-mounted pneumatic fenders are located on the weather deck

for mooring use during bunkering operations. These fenders are sized to allow for sufficient

stand-off distance between the bunkering vessel and the cruise ship. The davits allow for quick

deployment of the fenders, reducing the required time for mooring. Figure 8 depicts a typical

davit-mounted fender arrangement.

Figure 8. Fender Davit

Source: ttsgroup.com


Accommodations

The superstructure arrangement is laid out as most accommodation spaces are laid out.

The one major difference is that on 01 Deck there is the cargo control room and deck conference

room. This is to allow direct access to the top Weather Deck, where most of the cargo operations

would take place. Just below 01 Deck is Main Deck. Main Deck has some engine room

machinery arranged on it to help give ample room to all the important machinery. As of now our

vessel has staterooms for 18 crew members.

AREA VOLUME REPORT

The footprint and volume of each machinery and accommodation space was calculated to

verify the sizing of spaces. Shipboard experience was utilized to correctly size the spaces. See

Appendix F for tabularized area and volume data for each space.

CAPACITY PLAN

A capacity plan outlining the location and capacity of the various cargo and auxiliary tanks

onboard the vessel. The capacity plan is contained in Appendix G.

STRUCTURAL DESIGN

CONCEPTUAL MIDSHIP SECTION AND SECTION MODULUS

The design of the midship section for the vessel is based on the midship section design of

a 165K Membrane type LNG Carrier. This design served as a basis for an arrangement of the

structural elements. This design also aided in the selection of stiffeners for the design. A

longitudinal framing arrangement was used due to the operational profile of the vessel. The major

loads considered for the longitudinal strength of the vessel were buoyancy, wave induced loads

and weight at the full load condition. The structural arrangement produced for the vessel meets the

minimum section modulus requirement as well as the various plate thickness requirements

specified by ABS. Our structural midship section can be found in Appendix H.

RULES AND REGULATIONS

We based our structural design on the ABS Under 90 Steel Vessel Rules. We decided this

set of rules was the most applicable set of ABS structural rules for our design. The design

requirement is that we comply with ABS Marine Vessel Rules; however, the ABS Under 90 Steel

Vessel Rules are more conservative so we chose to follow those.


There are several rules relating to structural configuration in the ABS U90 SVR (U90 is

the short for under 90 m) that need to be met for our vessel to be classed. Even though our LOA

is 92.9 m, our scantling length is defined as 84.1 m which means our vessel’s applicable rules are

from the guide for vessels under 90 m. For our minimum section modulus requirement, ABS states

in ABS U90 SVR 3-2-1/3 that the hull girder section modulus is to be the maximum section

modulus either of equation 3-2-1/3.1. or equation 3-2-1/3.3.4 Equation 3-2-1/3.3.4 is given as: SM

= Mt / fp cm2-m. Mt is the total bending moment which is equivalent to the maximum algebraic

sum of the still water bending moment and the wave induced bending moment. The written

sections below explain in more depth the still water bending moment and wave induced bending

moment calculations. fp is the nominal permissible bending stress given by ABS as 1.784 tf/cm2.

Equation 3-2-1/3.1 is given as: SM = C1C2L2B(Cb + 0.7) cm

2-m. In this equation, C1 and C2 are

constants given by ABS, L is the scantling of the vessel, B is the breadth of the vessel, and Cb is

the block coefficient (all variables are specifically defined by ABS).

The ABS U90 SVR rules also outlined specific dimensional requirements for the

components that make up the ship structure. Detailed calculations for the minimum dimensions of

the components are contained in Appendix I. The method for determining the minimum bottom

shell plating thickness is outlined in ABS U90 SVR 3-2-2/3.3. The minimum bottom shell plating

thickness is a function of the frame spacing, depth, scantling draft, and the length between

perpendiculars of the vessel. The side shell plating thickness is described by ABS U90 SVR 3-2-

2/5 and is a function of the frame spacing, depth, draft, and length between perpendiculars for the

vessel. ABS U90 SVR 3-2-2/16 outlines the procedure for calculating the minimum bilge plating

thickness. The thickness of this component is a function of the girth spacing of the bilge

longitudinal, depth, draft, and length between perpendiculars of the vessel. The minimum required

deck plating thickness is outlined by ABS U90 SVR 3-2-3/3.3 and is a function of the longitudinal

frame spacing. The method for calculating the dimensions of the center girder at midships is

outlined in ABS U90 SVR 3-2-4/1.3. The minimum thickness of the girder is a function of the

length between perpendiculars of the vessel. The depth of the girder is a function of the breadth

and draft of the vessel. ABS U90 SVR 3-2-4/1.5 outlines the procedure for calculating the required

thickness of the side girders of the vessel. The thickness of the side girder is a function of the

length between perpendiculars of the vessel. The required inner bottom plating thickness is


dictated in ABS U90 SVR 3-2-4/1.13 and is a function of the length between perpendiculars of the

vessel and the longitudinal frame spacing.

LONGITUDINAL WEIGHT CURVE

We developed a longitudinal weight curve for our vessel in the full load condition. We

used the weights determined in the initial weights and centers estimate to create the full load

longitudinal weight curve. The weights and centers section later in the report details how we came

up with the values for each weighted section.

We distributed the hull structural weight over the full length of the according. The weight

distribution was scaled by the beam of the vessel at main deck to get an accurate distribution of

structural weight in the bow and stern region. The deckhouse and forecastle structural weight was

evenly distributed overs its longitudinal extents. The poopdeck’s structural weight was distributed

according to the beam at the main deck.

The portion of the outfit weight located at amidships was evenly distributed over the entire

length of the vessel. The portion of the outfit weight located in deckhouse was evenly distributed

over the footprint of the deckhouse. The portion of the outfit weight located in the machinery space

was evenly distributed over the length of the machinery space.

The weight of the propulsion plan and freshwater were evenly distributed over the length

of the machinery space. The weight of the diesel oil and lube oil were evenly distributed over the

footprint of their respective tanks. The weight of the crew and effects, and provision was evenly

distributed over the footprint of the house.

The cargo weight was distributed according to the cross-sectional area of tanks at the given

frame. The weight of water ballast for each set of tanks was distributed evenly over the length of

each set of tanks. The complete longitudinal weight curve is depicted below in Figure 9.


Figure 9: Longitudinal Weight Curve

BUOYANCY CURVE

We used Orca3D’s hydrostatics report to find the immersed area at each frame in the full

load condition of our vessel. Linear buoyancy was found multiplying the immersed area by the

specific weight of seawater. See the following figure for the buoyancy curve.

Figure 10. Buoyancy Curve


STILL WATER BENDING MOMENT CURVE

After finding the longitudinal weight distribution curve and the buoyancy curve, it is

possible to calculate the still water bending moment curve. To do this we first calculate the shear

force at every station. The shear force is the integral of the net load curve. The net load is the

difference between the weight and buoyancy force (depicted in Figure 11: Longitudinal Net Load

Curve). We carried out this integral with the trapezoidal method. After the shear forces are

calculated, the bending moment is calculated by using the same trapezoidal method to integrate

the shear force curve.

Figure 11: Longitudinal Net Load Curve


Figure 12: Shear Force and Bending Moment Diagram

WAVE INDUCED BENDING MOMENT CURVE

The wave induced bending moment curve is needed to find the minimum required section

modulus. ABS U90 SVR 3-2-1/3.3 outlines the procedure for finding the wave induced bending

moment curve. First, we are given ABS U90 SVR equation 3-2-1/3.3.3(a) which relates the

sagging moment and hogging moment amidships to the ABS defined constants k and C1 as well

as the previously mentioned L (scantling length), B (maximum breadth), and Cb (block coefficient)

as seen below.

Figure 13. ABS Hogging and Sagging Moment calculation

In addition to using these equations, the wave induced bending moment calculation

requires a distribution factor M described in ABS U90 SVR 3-2-1/3.3 Figure 14. ABS Wave

Induced Bending Moment Distribution Factor.


Figure 14. ABS Wave Induced Bending Moment Distribution Factor

This distribution factor is multiplied by the Mws and Mwh values from above to get the wave

bending moment. The total bending moment Mt is equal to the algebraic sum of the still water

bending moment and the wave induced bending moment.

MINIMUM REQUIRED SECTION MODULUS

Perhaps the most important calculation to designing our structure is determining the

minimum required section modulus. ABS U90 SVR 3-2-1/3.3.4 states that the required section

modulus is to be obtained by dividing the total bending moment (Mt) by the nominal permissible

bending stress fp. The total bending moment is calculated in the above section on wave induced

bending moment and the nominal permissible bending stress is defined by ABS as 1.784 tf/cm2.

VERIFICATION OF COMPLIANCE WITH ABS RULES

We verified our design complied with ABS rules by calculating the moment of inertia and

section modulus of our design structural midships section. The limiting section modulus for our

design was the section modulus to the top of the trunk deck stiffeners as the trunk deck stiffeners

are the farthest structural element from the neutral axis. The results of this calculation are

summarized below in Table 4 and can be found in Appendix H. The required section modulus is

the limiting variable for our design. This is because of the large distance between the neutral axis

and the top of the trunk deck stiffeners. Our design produces greater values for its section modulus


and moment of inertia than the minimum required values. We decided to not reduce the section

modulus of the design further due to the use of small stiffeners in the design. We did not reduce

the number of stiffeners because it would have increased the minimum plate thickness and may

have caused problems with local loads later in the design process.

Table 4. Designed and Required Section Modulus and Moment of Inertia

PROPULSION PLANT TRADE-OFF STUDY

DEFINITION OF CRITERIA

The following section outlines the selection of the propulsion plant for the vessel. The

selection of the appropriate powering and propulsion system was heavily influenced by several

factors specified in the owner’s requirements, as well as other criteria critical to the integration of

the plant into the design. The following factors were considered:

• EPA Tier IV and IMO Tier III Compliance

• Use of Electrical Component for Power generating and Propulsion systems

• High Degree of Maneuverability

• Powering Flexibility

• Spatial Efficiency

• Reliability/Redundancy

• Maintenance Cost

• Capital Cost

The primary criteria driving the propulsion plant selection were specified by the owner in

the Machinery, Propulsion, and Steering Systems Requirements. It was specifically requested that

the designers utilize green technologies to the greatest extent possible and integrate a major electric

component in the design of the propulsion system. The owner’s requirements further expand on

the environmentally conscientious, stating that the vessel must comply with EPA Tier 4 Emission

Standards. Compliance with this regulation is not only critical to the specifications requested by

Total Moment of Inertia (cm^2*m^2) 2.29E+05

SM Trunk Deck (cm^2*m) 2.28E+04

Required Total Moment of Inertia

(cm^2*m^2) 4.00E+04

Required SM Trunk Deck (cm^2*m) 1.58E+04


the owner, but it is integral to the operational region of the vessel. Additionally, the owner specified

that the propulsion system must provide the vessel with a high degree of maneuverability. It is

essential for the vessel to have the ability to come alongside the cruise vessels in a safe and efficient

manner. This will help minimize the need for supporting tugs and reduce the possibility of delays

to the demanding schedule of cruise vessels.

Powering flexibility, spatial efficiency, reliability, redundancy, maintenance cost, and

capital cost were additional criteria considered in the propulsion plant trade-off study. Powering

flexibility is defined as the ability of the power plant to match the powering requirements of various

loading conditions. Most propulsion plants are designed to perform optimally within a specific

loading range. Extended periods of operation outside this region can cause excessive wear on the

engine, increasing maintenance costs and decreasing the useful life of the asset. It is essential for

the selected power plant to provide the powering flexibility to meet the various loads seen across

transit, maneuvering, bunkering, and terminal loading operations. As outlined in the owner’s

requirements, the vessel must have a design transit speed of 14kts and top speed of 16kts. As seen

in the powering estimate section, there is a significant difference in the required propulsive power

for the 14kt transit and 16kt transit condition. It is critical for the propulsion plant to have the

ability to efficiently meet these two loading scenarios. Additionally, the power plant must have the

ability to match the loads required for maneuvering, bunkering and terminal loading operations.

While the loading for these three cases is much lower than for the described transit conditions, it

is still substantial due to the duration of these operations.

Spatial Efficiency is another critical design factor due to the special restrictions imposed

by the machinery spaces. The selected power plant must fit within the spatial limitations of the

machinery spaces and the propulsors must not extend below the baseline of the vessel.

Additionally, it is essential that the propulsion plant provide a high degree of reliability and

redundancy, allowing the vessel to fulfill its mission in the event of damage to the plant. In addition

to what was already mentioned, the maintenance cost and capital cost were also considered.

APPROACH

The selection of the main power plant and propulsion method utilized a progressive three

tier method to weigh the benefits and drawbacks of the considered systems. Systems were initially

sorted by fuel type due to the dependence of emission regulatory compliance on fuel type.


Categories consist of diesel, natural gas and duel fuel (diesel and natural gas). Propulsion plants in

each of these categories were further divided into sub-categories based on drive type consisting of

mechanical drive and diesel-electric drive. Systems were further categorized by propulsor type

into one of three groups: twin screw, z drive, and azi-pod.

TRADE-OFF STUDY

Fuel Selection

The fuel selection process began by listing out the potential benefits and drawbacks of

each proposed fuel. The results were then outlined in a “pros and cons list” alongside one another

as seen in Table 5.

Table 5. Fuel Type Pros and Cons

A dual fuel system was determined to be the optimal system for the bunkering vessel.

While dual fuel engines have a higher associated acquisition cost and require a specialized fuel

gas system, the system complies with the EPA Tier 4 emission standards. Dual fuel systems also

Pros Cons

-Fuel flexibility adds redundancy

-Proven and reliable system

Diesel

Natural Gas

-Eliminates use of propulsion

plant for BOG management

-Diesel fuel is more expensive

than LNG

-More complex than a

conventional diesel plant

-Meets EPA Tier 4 and IMO

Tier 3 Emissions Standards

-Larger cargo tanks required

for sufficient endurance



-Fuel readily availible

-Simple and proven -Requires additional

equipment for environmental

compliance

-System is expensive

-Fuel can only be bunkered at

the JAX LNG Terminal

-Additional method of BOG

management

-Meets EPA Tier 4 and IMO

Tier 3 Emissions Standards

Dual Fuel

-LNG is less expensive than

diesel fuel

-System is expensive

-LNG is less expensive than

diesel fuel

-Additional method of BOG

management


offer significant savings in operating expense, as natural gas is less expensive than ultra-low sulfur

diesel. Additionally, dual fuel provides additional endurance flexibility compared to a pure natural

gas system. If voyage is significantly prolonged and there is not sufficient LNG fuel onboard, the

vessel can operate the propulsion plant off a reserve diesel tank. In the event that the fuel gas

system fails, the diesel mode serves as a backup fuel supply system, adding a layer of resilience to

the vessel. Dual fuel systems also provide an additional method for managing boil-off gas.

Drive Type

The drive type for the vessel was determined using the same method utilized for the fuel

selection. The two drive systems considered for use were a diesel electric system and a

conventional mechanical drive system. A diesel electric system consists of a series of generators

which power electric propulsion motors. A traditional mechanical drive system consists of one or

more engines connected directly to the propulsors via a mechanical linkage. A power take-off

system is typically included in a mechanical drive system, allowing the vessel to utilize excess

power from the main engines to satisfy various electrical loads. The benefits and drawbacks of

each of these systems are outlined below in Table 6.

Table 6. Drive Type Pros and Cons

A diesel electric system was selected due to numerous advantages it presents in this

unique application. Unlike a mechanical drive system, the diesel electric system contains a

Pros Cons

-Only compatible with

mechanical propulsors

-Performs optimally at a

narrow range of powers

-Requires power-take off

system or generators for

additional electrical loads

-Meets significant electrical

component specified in Owner's

Requirements

-Simple and proven

-Inexpensive

-System is more expensive

than a conventional diesel

Multiple generators provide

additional redundancy

-Flexibility to match electrical

loads

-Requires additional electrical

components

-Larger spatial requirement



-Range of compatible propulsor

types

Diesel

Electric

System

Conventional

Mechanical

Drive


significant electrical component that complies with the owner’s request that propulsion system

contain a significant electrical component. Diesel electric systems also provide greater powering

flexibility in comparison to mechanical drive systems. There are significant differences in

powering requirements for the top speed condition, design transit condition, maneuvering, and

various cargo operation conditions. The diesel electric system allows generators to provide the

required power by operating the generators in various configurations, where each generator is run

at an optimal loading condition. This can help reduce wear and prolong the useful life of the

generators. This is a clear advantage compared to the mechanical drive system, which would spend

most of its life operating well below its designed operating region. Another benefit of the diesel

electric system is the redundancy offered by multiple generators. The generators can be selected

in manner that allows the vessel to meet its design transit speed with any single generator offline.

It is important to note that there are a few potential drawbacks of the diesel electric system such as

higher cost, increased complexity, and potential issues regarding spatial efficiency. While these

factors are clearly outweighed by the benefits of the system, it is important to recognize these

drawbacks.

Propulsor Type

The three propulsor types considered for use were z-drive thrusters, azimuth thrusters,

and twin screw propulsors. The benefits and drawbacks of each were outlined as shown in Table

7. Each system was compared against the other candidates to determine the optimal choice for the

vessel.


Table 7. Propulsor Type Pros and Cons

The twin screw propulsion system best fit the needs of the vessel and presented several

distinct advantages compared to the other systems. While the z-drive and azimuth thrusters provide

better maneuverability than twin screw propulsors, these two systems have significant spatial

limitations imposed by the draft of this specific vessel. After researching the requirements for these

thruster configurations, it was determined that there is no available podded propulsion system on

the market that provides the required thrust without protruding below the baseline of the vessel.

Significant modification would need to be made to the hull form to use either of these propulsion

systems. With the addition of a bow thruster, the performance characteristics of the twin screw

electric propulsion system are sufficient to meet the high degree of maneuverability specified in

the owner’s requirements. Techniques, such as prop splitting, can be used in conjunction with the

bow thruster to precisely position the vessel alongside cruise vessels. A key advantage of twin

Pros Cons

-Requires sufficient space for

mounting along the underside

of the vessel

-Fairly high degree of

maneuverability when used with

a bow thruster

-Requires bow thruster

-Lower degree of

manueverability compared to

other systems

-Expensive

-Complex

-Requires sufficient space for

mounting along the underside

of the vessel

-Very high degree of

maneuverability

-Fewer mechanical linkages

make the system robust

-Complex

-Expensive

Twin Screw

-Greater mounting flexibility

compared to other propulsor

types

-Inexpensive

-Simple and robust

-Mechanical linkages create

additional points of failure

Azimuth

Thrusters

-Very high degree of

maneuverability

Z-Drive


screw propulsors is the simplicity of the design which reduces failure points and adds a degree of

resilience to the propulsion system.

POWER PLANT SELECTION

The dual fuel diesel electric twin screw propulsion system was further defined by

selecting specific generators and propulsors. To aid in the selection of the optimum generator

configuration, the propulsive power requirements from the Holtrop analysis were used to estimate

the range of loading conditions seen by the system.

Dual fuel generator sets produced by MAN B&W and Wärtsilä were identified as the

best potential candidates for use in the vessel due to the wide use of dual fuel products from these

two manufacturers across the marine industry. After researching various models from each

manufacturer, it was determined that generator sets from Wärtsilä would be better suited for this

design due to the abundance of technical data on Wärtsilä’s product line. While MAN B&W’s

high-pressure dual fuel system has potential advantages, such as reduced methane slip, it was

difficult to find the necessary technical data to perform a proper analysis on these generator sets.

It is critical to have data, such as specific fuel consumption, to properly select an optimal generator

for this application.

The optimal generator configuration for the vessel consists of two Wärtsilä 8L34DF

gensets and two Wärtsilä 6L20DF gensets. This configuration offers optimal performance across

a range of expected loading conditions. Table 7 displays the rated power provided by this

configuration.

Table 8. Wärtsilä Generator Configuration

MACHINERY ARRANGEMENT

The machinery space on our vessel has three levels. The engine control room is located on

the main deck level. The machine shop is located on this level to give the engineers easy access to

it from the engine control room. Most of the quiet equipment is located on this level to minimize

the noise that enters the accommodations block from the machinery space. The gas combustion

Genset Rated Power (kW) Number Sub Total Wartsila 8L34DF: Specific Fuel Consumption Data

8L34DF 3490 2 6980

6L20DF 1065 2 2130

Total 9110


unit is located on this level and is separated from the rest of the machinery space by a double

walled bulkhead, as required by the IGC Code.

The 1st platform houses our vessels generators. This deck has plenty of head room to allow

the diesel engines to be maintained. The compressors skid is also located on 1st platform. The

steering gear is located on this level and is separated from the main machinery space by a

watertight bulkhead.

The electric propulsion motors are located on 2nd platform. The fuel and oil tanks are also

located in this level to help lower the VCG of our vessel. The pumps skid is located on this level

to increase the net positive suction head available (NPSHa) for the various pumps. The machinery

arrangement for our vessel can be found in Appendix J.

H, M, AND E SYSTEMS AND EQUIPMENT

We based our machinery list of our sea term experience aboard commercial vessels and

general knowledge of the function of shipboard systems. Lists of machinery to be included in each

system are listed below.


Equipment Quantity Equipment Quantity

Purifier 2 Air Receiver 1

Feed Pump 2 High Pressure Compressor 2

Piping TBD Emergency Air Receiver 1

Valves TBD Emergency Air Compressor 1

Piping TBD

Valves TBD


MGO Transfer Pump 1 Emergency Diesel Generator 1

MGO Storage Tank 2 Diesel Tank 1

MGO Overflow Tank 1 Bus Tie Connector 1

Piping TBD Control Panel 1

Valves TBD Piping TBD

Valves TBD


MGO Supply Pump 1 Potable Water tanks 2

MGO Service Tank 1 Potable Water Pump 2

Piping TBD Sterilization Unit 1

Valves TBD Calorifier 1

Piping TBD

Valves TBD


Tanks 2 MSD 1

Black Water Pump 1 Tanks 2

Piping TBD Black Water Pump 1


Valves TBD

Fuel Oil Purifying Start Air

Emergency Diesel GeneratorFuel Oil Transfer

Grey Water

Fuel Oil Supply

Black Water

Potable Water



Purifier 2 Air Receiver 1

Feed Pump 2 Compressor 1

Lube Oil Heaters 2 Air Drier 1

Piping TBD Piping TBD

Valves TBD Valves TBD


Lube Transfer Pump 1 Inert Gas Generator 1

Lube Oil Storage Tank 1 Piping TBD

Piping TBD Valves TBD

Valves TBD


Bilge Tanks TBD Main Fire Pump 1

Bilge Pumps 2 Pipes TBD

Oily water seperator 1 Valves TBD

Piping TBD Emergency Fire Pump 1

Valves TBD Pipes TBD

Valves TBD


Hydraulic Oil Tank 1 Composite Boiler 1

Hydraulic Oil Pump 1 Condenser 1

Hydraulic Power Unit 1 Feed Pump 1

Piping TBD Piping TBD


Service/Control Air

Inert Gas Generator

Lube Oil Purifying

Lube Oil Transfer

Hydraulic System

Fire System

Service Steam System

Bilge System



HEX with LT Cooling 1 Sea Chest 2

Circulating Pump 2 Circulating Pump 2

Expansion Tank 1 HEX with LT Cooling 1

HT Cooling Pumps 1 MGPS 1

Piping TBD Pipes TBD



Circulating Pump 1 Incinerator 1

Expansion Tank 1 Sludge Pump 1

Pipes TBD Pipes TBD



Compressor 1 Freshwater pump 1

Ventilation ducts TBD Evaporator 1

Air Handler Unit 1 Freshwater Tank 1

Pipes TBD Piping TBD



Compressor 1 Ballast Water Pumps 2

Evaporator 3 Ballast Treatment System 1

Piping TBD Ballast Tanks 15


Valves TBD

High Temperature Cooling

Low Temperature Cooling

Sea Water Cooling

Incinerator

FreshwaterHVAC

Refrigeration System Ballast System


CARGO TRANSFER SYSTEM

OVERVIEW

The cargo containment and cargo transfer system are designed to allow the vessel to

seamlessly meet the specified flow rates and rigorous transfer schedule required for bunkering and

terminal loading operations. The vessel utilizes two Type C independent tanks for cargo

containment. Two 5-ton hose cranes are included to allow for the transfer of cargo hoses during

bunkering operations. The system is required to bunker cargo to the cruise ships at a transfer rate

of 1000 cuM/hr and receive cargo from the terminal at a transfer rate of 2400gpm. To achieve this,

the cargo transfer system utilizes two main cargo pumps, each with a capacity of 500cuM/hr.

Additionally, two 16 cuM/hr stripping pumps are utilized for cooling the system down prior to

transfer operations and two 2.6cuM/hr fuel supply pumps are used to supply LNG to the fuel

system. Two high duty compressors, two low duty compressors, and a forcing vaporizer are

included to manage vapor during bunkering, loading and fuel supply operations. In addition to the

use of dual fuel engines to manage boil off gas (BOG), a gas combustion unit is included BOG

management redundancy. Table 9 summarizes the mission specific equipment onboard the vessel.

Table 9. Mission Specific Equipment

DISCUSSION OF OPTIONS CONSIDERED

System Boundaries

Our LNG cargo transfer system starts at the suction the two cargo pumps and ends at the

two manifold connections on main deck or before the dual fuel engines located in the engine room.

An additional boundary was placed at each manifold because the shore side terminal is responsible

for the design of the terminal transfer arms. The system boundry for the fuel supply to the dual

fuel engines is located before the fuel gas heater. We did this because we considered beyond the

gas fuel heater to be the responsibility of the designer in charge of the fuel gas system.

Cargo Equipment

2x 5 Ton Hose Crane

2x 500 cuM/hr Cargo Pumps

2x 16 cuM/hr Stripping Pumps

2x 2.6 cuM/hr Fuel Pumps

2x 2930 cuM/hr HD Compressor

2x LD 1765 cuM/hr LD Compressor

1x Gas Combustion Unit

2x Type-C Independent Tank


Design Considerations

Several considerations were made in the decision-making process of arranging our

preliminary schematic. The selection of dual fuel engines heavily influenced the design of the

cargo transfer system. The driving factor of this decision came from our Ship Design I design

statement. It stated, “As a minimum, EPA tier 4 emissions requirements or equivalent are to be

met”. Using dual fuel engines meets these emissions requirements. Using a dual fuel engine in

tandem with a diesel-electric power plant would also allow for us to have a very flexible engine

room arrangement. The choice of dual fuel engines required the addition of a boil-off gas (BOG)

management system. This was another requirement in our design statement which stated under

mission systems/special requirements, “A handling system for boil-off gas (BOG), by means of

liquefaction, thermal oxidation, or fuel sharing, is to be fitted”. We also decided to include a gas

combustion unit (GCU) to provide additional redundancy in BOG management. This unit can be

operated in parallel with the duel fuel system to provide additional vapor management or act as a

standalone management solution. By choosing the fuel sharing option for our dual fuel engines

and utilizing a gas combustion unit, we ruled out the need for a reliquification plant onboard. Since

our bunkering vessel is transporting relatively low amounts of LNG on a short term, repetitive

schedule, we further cemented our decision of excluding a reliquification plant from the design.

We relied heavily on several publications produced by Society of International Gas Tanker

and Terminal Operators (SIGTTO) during the design of our additional schematic. These

publications include Liquified Gas Handling Principals 3rd Edition, The Selection and Testing of

Valves for LNG Applications, and LNG Marine Loading Arms and Manifold Draining, Purging

and Disconnection Procedure. We received additional advice on operational procedures from our

advisors as well as other industry professionals. The piping arrangement for our system was

determined by identifying each operational scenario and determining the resulting load placed on

the respective components. We determined our initial piping arrangement by tracing out the

required flow paths for each case. Valves were then added to the model according to operational

conditions and the reliability required at the point in question. Globe valves are reliable even under

cryogenic conditions and are optimal for isolating individual components locally. Butterfly valves

were placed at junctions between main cargo lines and smaller system branches. Butterfly valves

were chosen for this application due to their weight, simplicity, and their compatibility with larger

pipe sizes. Additionally, Emergency Shut Down (ESD) valves were places at each manifold and


at the liquid and vapor headers of each tank. The placement of these valves at these specific

locations is required by the IGC Code and allows the cargo system to automatically shut down in

the event of an emergency. Throughout the design process, we continuously adjusted the initial

schematic to reflect design choices.

DESCRIPTION OF GOVERNING OPERATING CASES

For our cargo transfer system, we looked at the governing cases that the various

compressors and pumps would be used in during the operation of our system. We determined the

governing operating cases to be loading LNG cargo, bunkering LNG cargo, providing fuel gas to

the engines, and spraying down the tanks.

Loading LNG Cargo

Our mentor, Tom Sullivan, provided us with the maximum cargo transfer rate from the

Jacksonville, FL based terminal our bunker vessel will load from. The maximum cargo transfer

rate is 2400gpm (545cuM/hr). Loading LNG cargo occurs once every 14 days and takes

approximately 13 hours to complete. For this operating case, the LNG enters the system through

the manifold, travels through the main cargo lines, ends up at the cargo header, and finally is

discharged into the cargo tanks. As LNG enters the tank, the boil-off gas (BOG) generation rate

increases resulting in additional vapor generation. While some of this vapor is displaced naturally,

high-duty compressors are needed to move the fluid through the vapor lines up to the vapor

manifold and back to the terminal. A portion of this BOG is diverted to the low-duty compressor

to be sent to the engine room for use as fuel. The BOG generation rate is critical to determining

the proper vapor flow rates. We estimated the generation rate of boil-off gas using the BOG

generation rate of a similar cargo operation described in “Dynamic Optimization of Boil-Off Gas

Generation for Different Time Limits in Liquid Natural Gas Bunkering” by Yude Shao,

Yoonhyeok Lee, and Hokeun Kang. We estimated the maximum BOG generation rate by

interpolating off data from the model contained in the paper. We then doubled this interpolated

value to account for the high degree of variability in BOG generation during STS operations and

our higher cargo transfer rate.

Bunkering LNG Cargo

The flowrate for bunker operation is required to be 1,000 cuM/hr per our vessel’s design

requirements. Bunkering LNG cargo occurs twice every 14 days and takes approximately 7 hours


to complete. For this operating case, the LNG is pumped out of both cargo tanks simultaneously,

directed through the main cargo lines, and flows out of the manifold to the receiving cruise ship

tank. This makes the maximum flow 500cuM/hr using the two main cargo pumps for each tank.

To determine the vapor flow rates for this application, it was assumed that the BOG generation

rate was the same as the rate during cargo loading.

Supplying Fuel Gas to the Engine Room

Our bunker vessel will be using LNG as its main fuel source for its two sets of dual fuel

diesel electric gensets. In general, this operating case is occurring continuously, but vapor is

consumed at a faster rate while the vessel is underway. To obtain an accurate fuel consumption

estimate, we first estimated various power requirements for transit, maneuvering, bunkering and

loading operations referencing: “A Case Study on Boil-Off-Gas Minimization for LNG Bunkering

Vessel Using Energy Storage System” authored by (Kyunghwa Kim, 2019). Following the same

fuel consumption calculation methodology outlined in the paper, we estimated fuel consumption

rates for various dual fuel generators using data obtained from Wärtsilä. We utilized both a generic

LNG heating value as well as a calculated heating value for the composition for the LNG from the

Jacksonville terminal. To determine the highest possible flow rate for the fuel gas supply system,

we specifically modeled the system during operation at maximum service speed. The maximum

fuel flow rate is 1,765cuM/hr of vaporized LNG. Although this seems like a high number, it is

important to keep in mind that liquified natural gas is 1/600th the volume of natural gas vapor.

Spraying Down Tanks

The main cargo tanks must be cooled down prior to loading cargo from the shore side

terminal. The cargo system features a spray system which cools the cargo tanks using a

phenomenon known as evaporative cooling. In each tank, stripping pumps pump heel from the

bottom of the tank through stripping lines to a set of nozzles running along the top of the tank. The

LNG droplets evaporate as they exit the nozzles, cooling the tank. Tanks are typically sprayed

down in the hours prior to arriving at the terminal. The maximum flow rate for spraying down the

tanks was determined by researching stripping pump capacities on LNG carriers and LNG

bunkering vessels. We determined the maximum possible flow rate to be 16cuM/hr. The maximum

flowrate for this operation is 16cuM/hr.


SYSTEM LAYOUT ON GENERAL ARRANGEMENT

Our LNG cargo transfer system on the general arrangement of our LNG bunkering vessel

is available in Appendix K. Various components and piping of the system are depicted and labeled

accordingly. The arrangement of our system was created so that it complied with the rules,

regulations, and requirements outlined in the design requirements & considerations document.

SYSTEM FLOW CALCULATION

We built a model of our cargo transfer system in PIPE-FLO Advantage 17 to determine

the hydraulic characteristics of our system. The modelling of natural gas vapor in PipeFlo

presented some difficulty. PipeFlo conducts an incompressible analysis of the system which

produced unrealistic results as the compressibility effects of vapor are significant to the system.

PipeFlo recommends using different fluid zones to account for the change in pressure’s effect on

compressible fluid properties. We used different fluid zones to evaluate fluid properties at the

closest quarter bar of pressure. This allows an incompressible analysis to produce reasonable

values for a compressible fluid system.

We modeled the LNG fuel tank in the cruise ship at the correct relative height to our system

and used an estimated hose length of 25m. This was easier and more accurate than trying to model

the back pressure at the manifold from the cruise ship. We followed Wärtsilä's product guide for

our vessel’s selected generators to estimate the back pressure from the engine room in the vapor

piping to the engine room. The vapor to the engine passes through a gas valve unit (GVU), which

accounts for most of the pressure drop in the system. Wärtsilä estimates a 1.2 bar pressure drop

over a typical GVU. We added 0.1 bar of pressure drop to account for other head losses and a back

pressure from the engine, which added to a total estimated back pressure of 1.3 bar. We modeled

the tank surface pressure as 0.0 bar gauge. We estimated the back pressure at the vapor manifold

to be 0.1 bar gauge to account for the head-loss in the onshore vapor handling system.

The system flow calculations for all the governing cases are attached in Appendix B. A

summary of the design flowrates and heads for the governing cases are summarized in Table 10

below.


Table 10. Summary of Flowrates and Heads of Governing Cases

PUMP SELECTION

Cargo Pumps

We selected the SMR 250 single stage pump made by Shinko-Nishishiba. The SMR 250

is a removable in-tank pump used for the discharge of LNG, LPG, or DME. It is typically used as

an emergency cargo pump on larger LNG carriers. The pump’s ball bearings are lubricated using

the liquid being pumped. The pump is fitted with an inducer to reduce the NPSH required. The

pump is hydrodynamically balanced using a balance sleeve to reduce the loading on thrust bearing.

The induction motor has insulation to allow it to operate at cryogenic temperatures. The pump can

be removed from the tank for maintenance by lifting the pump up its installed column in the cargo

tank.

Stripping Pumps

We selected the Svanehoj EFP 24-3 for our vessel’s stripping pump. The EFP 24-3 has no

tank connections below the liquid level and no electrical components inside the tank. This

minimizes the generator of boil-off gas from the heat of the electrical components. The pump can

be retracted with liquid still in the tank. This allows for maintenance to occur well the ship is in

service. The pump is fitted with an inducer to lower the NPSH required of the pump (only 2m at

the design point).

Fuel Supply Pump

We selected the Artika 120 3S by Vanzetti Engineering for our vessel’s fuel supply pump.

The Artika 120 is designed for low pressure marine engine fuel gas systems, such as the one fitted

on our vessel. The pump is already certified by ABS for this application and follows IGC

guidelines. The pump features an integrated motor connected with cryogenic power cables. The

pump is lubricated continuously with LNG, reducing maintenance costs. The pump is fitted with

a helical inducer to minimize NPSH required. The pump is designed to be installed within the LNG

tank in a sump.

Flow Rate

(cuM/hr) Head (m)

Flow Rate

(cuM/hr) Head (m)

Flow Rate

(cuM/hr) Head (m)

Flow Rate

(cuM/hr)

Adiabatic

Head (m)

Flow Rate

(cuM/hr)

Adiabatic

Head (m)

Bunkering Operations 500 143 0 0 2.6 133.3 0 0 1765 5858

Cargo Loading 0 0 0 0 2.6 133.3 2930 2345 1765 6031

Supplying Main Engine 0 0 0 0 2.6 133.3 0 0 1765 5804

Spraying Down Tanks 0 0 16 49 2.6 133.3 0 0 1765 5804

Cargo Pumps Stripping Pumps HD Compressor LD CompressorFuel Supply Pumps


SYSTEM HEAD CURVES

System head curves were generated for the governing case for each of the pumps or

compressors. The pump curves of the selected pumps have been overlaid on their respective

governing case. These curves were cargo discharge for the main cargo pumps, supplying the main

engine fuel gas for the low duty compressors (LD compressor), cargo loading for the high duty

compressors, supplying the generators with fuel for the fuel supply pump, and spraying down the

tank for the stripping pumps. The system head and pump curves can be found below. The system

curve for the low duty compressor looks different because of the high back pressure from the

engine room. We did not have data on how the pressure drop across the gas value unit varies with

flowrates. It was treated as a constant, leading to the high static head shown on the system head

curve.

Figure 15. System Head Curve for Cargo Pumps


Figure 16. System Head Curve for LD Compressors

Figure 17. System Head Curve for HD Compressors

0

1000

2000

3000

4000

5000

6000

7000

0 500 1000 1500 2000 2500

Ad

iab

atic

Hea

d (

m)

Flowrate (cuM/hr)

System Head Curve for the LD Compressors

System Head Curve Operating Point

0

500

1000

1500

2000

2500

3000

3500

0 500 1000 1500 2000 2500 3000 3500 4000

Ad

iab

atic

Hea

d (

m)

Flowrate (cuM/hr)

System Head Curve for HD Compressors

System Head Curve Operating Point


Figure 18. System Head Curve for Stripping Pump

Figure 19. System Head Curve for Fuel Supply Pump


OPTIMIZATION

The cargo transfer system was optimized using the annualized cost optimization method.

In this analysis, the capital expenditure (CAPEX) of the system was defined as the acquisition and

installation cost of the piping material, the pipe fittings, the pumps, and the compressors. Due to

the nature of available pricing data, a pricing model was developed to determine pipe cost per

meter as a function of inner diameter. The model consisted of a power-regression model fitted to

standard carbon steel pricing data. A cost correction factor was then applied to the regression

coefficient to account for the cost ratio between the price of carbon steel pipe and the stainless-

steel pipe used in the system. The cost of major components, minor components, and bends were

defined as a function of the cost of pipe at a specified equivalent length. CAPEX was calculated

by discounting the capital cost over the expected lifetime of the system of 20 years at an interest

rate of seven percent. A function was derived expressing the optimal inner diameter of pipe as a

function of the annualized cost of piping material, piping components, maximum flow rate, energy

input, cargo fluid properties, and maintenance.

Using data from the PipeFlo model, the system was divided into 14 piping sections based

on state of the operating fluid, maximum flow rate, primary usage, and inner diameter.

Approximate yearly operating timeframes were calculated for each of these groups based on the

operation profile of the system defines these categories. The characteristics are summarized in

Table 11 below.

Table 11. Pipe Characteristics

For each piping section, the optimum inner diameter was calculated using the associated

characteristics. The calculated optimum diameters were utilized in conjunction with educated

discretion to select pipe sizes for each group. Using the selected standard diameters, the annualized


acquisition, construction, and maintenance cost of the system was calculated. The operational cost

of the system was computed using the fuel pricing per unit energy, fuel to energy efficiency,

required power, and yearly operating time for each pump and compressor. The annualized capital

cost and operating cost were then summed to determine the total annualized cost of the system.

The optimization required several iterations to yield the lowest possible lifecycle cost. At

the end of each iteration, the chosen diameters were input into Pipe Flo to determine the required

pump and compressor power. These new power values were used in conjunction with the selected

diameters

4200 cubic meter lng bunkering vessel concept design · 2021. 1. 5. · dr. james a. lisnyk student...

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