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SMK4532 Ship Design II Ver. JULY 2009

© KOH Kho King, Yahya Samian, Omar Yaakob 0

SMK4532 Ship Design II

Lecture Notes

(Version JULY 2009)

Prepared by KOH Kho King, Yahya Samian & Omar Yaakob

Department of Marine Technology Faculty of Mechanical Engineering

Universiti Teknologi Malaysia 81310 UTM Skudai

Johor Malaysia



Chapter 1 Introduction To carry out various activities at sea, rivers and lakes, man uses various types of marine structures, fixed and floating. The structures must be designed and built in various sizes, shapes and sophistication. Some of them are small and simple such as a canoe or a raft while others are large and complicated such as an aircraft carrier or a semi-submersible oil drilling platform. Naval architecture is an engineering field covering the technology in design of ships and floating structures. The persons having this expertise are called naval architects. To build these structures, shipbuilders require design plans and guidelines prepared by naval architects. Knowledge in naval architecture is used to carry out design calculation and to produce plans which can be used by the shipyards. Although man has been using marine transport for a long time, not all these vehicles are designed and constructed using naval architecture knowledge. In fact the discipline of knowledge on ship design and naval architecture only appeared in the seventeenth century. Prior to that, shipbuilding is not based on science and technology but rather on the skills of the master craftsmen. This dependence on master craftsmen for shipbuilding can be traced back to the earliest civilization of Egypt, Greek and China. Similarly the war ships and exploration vessels built by the Romans, Muslims as well as the European colonial powers were not built using scientific methods. By the seventeenth century a number of scientists and engineers tried to apply science and mathematical methods in ship design. Among the earliest was sir Anthony Deane who wrote Doctrine of Naval Architecture in 1670. Among others, he put forward a method to determine the draught of the ship before it was built. Since then, a number of scientists and engineers continued to study and document various fields of naval architecture. In 1860, a professional body comprising of naval architects was formed under the name Institution of Naval Architects. A hundred years later the name was changed to Royal Institution of Naval Architects. A naval architects works to determine the size and shape of a ship tailored to its intended use. In addition, he estimates its stability, propulsive power as well as calculates the size and strength of its structure and the impact of waves on the vessel. The types of machinery and equipment to be installed, materials to be used and layout of ship are also determined based on naval architectural knowledge. An essential tool for transmission of information about ships is ship drawing. Using the drawings, designers, engineers and builders can share information about the ship to be built. Calculations can be made and plans for construction can be made. In this course, participants will learn about ship drawings in particular the lines plan; being the most important drawing in any ship design process.



Chapter 2 Basic Term, Terminologies and Symbols

After perpendicular(AP)

This is represented by a line which is perpendicular to the intersection of the after edge of the rudder-post with the designed load water-line. This is the case for both single- and twin-screw merchant ships. For some classes of warships, and for merchant ships having no rudder-post, the after perpendicular is taken as the centre-line of the rudder stock.

Amidships ( ) This is the point midway between the forward and after perpendiculars.

Breadth moulded (Bmld)

This is the maximum beam, or breadth, of the ship measured inside the inner shell strakes of plating, and usually occurs amidships.

Breadth extreme (BExt) This is the maximum breadth including all side plating, straps, etc.

Block coefficient (CB) This is a measure of the fullness of the form of the ship and is the ratio of the volume of displacement to a given water-line, and the volume of the circumscribing solid of constant rectangular cross-section having the same length, breadth and draught as the ship. ie: CB = ÷ (L x B x T) The LPP is normally used in calculating the value of CB which varies with the type of ship. Fast ships 0.50-0.65 (fine form) Ordinary ships 0.65-0.75 (moderate form) Slow ships 0.75-0.85 (full form)

Camber or round of beam

This is the transverse curvature given to the decks, and is measured by the difference between the heights of the deck at side and centre. The amount of camber amidships is often one-fiftieth of the beam of the ship.

Coefficients of form Form is used as a general term to describe the shape of the ship's hull; and when comparing one ship's form with another, the naval architect makes use of a number of coefficients. These coefficients are of great use in power, stability, strength and design calculations.

Centre of flotation (F) This is the centre of the area, or centroid, of the water-plane of a ship. For small angles of trim consecutive water-lines pass through F. The location is normally on the centerline and longitudinally the distance from AP or amidships is referred to as LCF

Centre of buoyancy (B)

This is the centroid of the underwater form of a ship, and is the point through which the total force of buoyancy may be assumed to act. Its position is defined by: (a) KB the vertical distance above the base, sometimes referred to as VCB (b) LCB the longitudinal distance measured either from amidships or AP or FP.



Centre of gravity (G) This is the point through which the total weight of the ship may be assumed to act. It also is defined by: (a) KG the vertical distance above the base (b) LCG the longitudinal distance measured either from amidships or AP or FP

Depth moulded (Dmld) This is the vertical distance between the moulded base line and the top of the beams of the uppermost continuous deck measured at the side amidships.

Draught moulded (Tmld)

This is the draught measured to any water-line, either forward or aft, using the moulded base line as a datum.

Draught extreme (TExt) This is obtained by adding to the draught moulded the distance between the moulded base line and a line touching the lowest point of the underside of the keel. This line is continued to the FP and AP, where it is used as the datum for the sets of draught marks.

Displacement This equals the volume ( m3) , weight ( tonnes), or mass of water displaced by the hull.

Displacement as a volume ( )

This is the size of the hole in the water occupied by the ship measured in cubic metres. There is no density correction.

Displacement as a weight ( )

This is the weight of water displaced by the ship and equals the volume displaced multiplied by a constant representing the density of water, ie: In fresh water = x 1000 kg/m³ In sea water = x 1025 kg/m³ The displacement weight of a ship can vary according to circumstances and position in the world, although displacement weight and ship weight are equal when the ship is at rest in equilibrium in still water.

Displacement moulded

This is the mass of water which would be displaced by the moulded lines of the ship when floating at the designed loadwater-line.

Deadweight This is the difference between the extreme displacement at any draught and the lightship displacement, and is sometimes known as the burden. This is the measure of a ship's capacity to carry cargo, fuel, passengers, stores, etc, expressed in tonnes. It is the difference in displacement in tonnes between the light and loaded conditions. = Lightship weight + Deadweight The size of tankers is often given in terms of deadweight tonnage. Ships are usually chartered on the deadweight tonnage basis.

Forward perpendicular (FP)

This is represented by a line which is perpendicular to the intersection of the designed load water-line with the forward side of the stem.

Flat of keel This is the amount of flat bottom plating on each side of the centre girder.

Flare This is the outward curvature of the hull surface above the water-line and is the opposite of tumble-home.

Freeboard This may be considered to be the height amidships, of the freeboard deck at side above the normal summer load water-line.

Tonnage The weight of the cargo of a merchant ship.

GML Longitudinal metacentric height measured from centre of gravity

GMT Transverse metacentric height measured from centre of gravity

Gross tonnage (GRT) This represents the total cubic capacity of a ship available for the carriage of cargo. It has no relationship to weight although 1.13 m³ are taken as 1 ton. This is a measure of the under-deck tonnage with the addition of 'tween-deck



spaces and enclosed spaces above the upper deck. Certain spaces are exempted from measurement. The size of most ordinary merchant ships is quoted in terms of gross tonnage.

Heel (∅) This is the amount of inclination of the ship in the transverse direction, and is usually measured in degrees.

Length between perpendiculars (LBP or LPP)

This is the horizontal distance between the forward and after perpendiculars.

Length on the designed load water-line (LWL)

This is the length, as measured on the water-line of the ship when floating in still water in the loaded, or designed, condition.

Length overall (LOA) This is the length measured from the extreme point forward to the extreme point aft.

Lightship displacement

This equals the extreme displacement of the ship when fully equipped and ready to proceed to sea, but with no crew, passengers, stores, fuel, water, or cargo on board.

MCT1CM Moment to change trim 1 cm, MCT1CM = GML ≈ BML 100 L 100L

Midship section This is the transverse section of the ship amidships. For a warship, amidships may be midway between the ends of the LWL.

Moulded base line This represents the lowest extremity of the moulded surface of the ship. At the point where this line cuts the midship section a horizontal line is drawn, and it is this line which acts as the datum, or base line, for all hydrostatic calculations. This line may, or may not, be parallel to the LWL depending on the type of ship.

Midship section area coefficient(CM)

This is the ratio of the immersed area of the midship section to the area of the circumscribing rectangle having a breadth equal to the breadth of the ship and a depth equal to the draught. ie: CM = AM ÷ (B x T) CM values range from about 0.85 for fast ships to 0.99 for slow ships.

Net or register tonnage

This represents the volume obtained after deductions of nonfreight earning spaces have been made from GRT.

Prismatic coefficient (CP)

This is the ratio of the volume of displacement of the ship to the volume of the circumscribing solid having a constant section equal to the immersed midship section area AM, and a length equal to the LPP ie CP = ÷ (AM x L) The Cp is a measure of the longitudinal distribution of displacement of the ship, and its value ranges from about 0.55 for fine ships to 0.85 for full ships.

Rise of floor This is the amount by which the line of the outer bottom plating amidships rises above the base line, when continued to the moulded breadth lines at each side.

Sheer This is the curvature given to the decks in the longitudinal direction, and is measured at any point by the difference between the height at side at that point and the height at side amidships. The amount of sheer forward is often twice the sheer aft.

Trim This is the difference between the draughts forward and aft. If the draught forward is greater than the draught aft it is called trim by the head, or bow. If the draught aft is greater, it is called trim by the stern.



Tumble-home This is the amount by which the midship section falls in from the half-breadth line at any particular depth.

Tonnes per centimetre (TPC)

This is the mass which must be added to, or deducted from, a ship in order to change its mean draught by 1 cm.

Water-plane area coefficient(CWP)

This is the ratio of the area of the water-plane to the area of the circumscribing rectangle having a length equal to the LPP and a breadth equal to B. ie: CWP = AW ÷ (L x B) The range of values is from about 0.70 for a fine ship to 0.90 for a full ship.



Source: http://www.dynagen.co.za/eugene/hulls/terms.html



Chapter 3 Introduction to Ship Drawing 3.1 INTRODUCTION

Drawing is a communication language that uses graphics to represent an object, idea, design etc. The use of drawing as a means of communication can be traced back since the ancient Egypt. As in old saying “A single picture saved thousand words“ has made drawing as one of the most important entity and plays important roles in engineering fields. Ship is one of the engineering products that require a lot of drawings to represent its unique shape, function, components, structures, construction process etc. Therefore it is essential for those who are involved in shipbuilding industry to understand the various types of ship drawing and know how to draw them. The session of this short course begins with the introduction on various types of ship drawing, its importance, and the basic concept of orthographic views applied in ship drawing. However its main focus is on the step by step procedure of preparing a lines plan drawing that represents the shape of the ship’s hull. Its aim is to provide hands on experience to the reader on how ship lines plan is prepared from scratch. 3.2 TYPES OF SHIP DRAWINGS In general, drawings that associates with ship buildings can be divided into the following categories:

i) Lines Plan Drawing ii) General Arrangement Drawing iii) Shell Expansion Drawing iv) Schematic Systems Drawing v) Detail / Production Drawing vi) 3-D Product Drawing

These are the general drawings that might appear in the ship drawings, but not all naval architects presented their designs with all the above. Some naval architects presented only lines plan, general arrangement, shell expansion, and production drawings. With the advance of computer technology, naval architects are moving towards presenting their design in the 3-dimensions product drawing. The following sections will give some intro and example on the lines plan drawing, general arrangement drawing, shell expansion drawing and detail/production drawing.



3.2.1 Lines Plan The exterior form of a ship’s hull is a curved surface defined by the lines plan drawing, or simply “the lines”. Precise and unambiguous means are needed to describe this surface, in as much as the ship’s form must be configured to accommodate all internals, must meet constraints of buoyancy, stability, speed and power, and seakeeping, and must be “build able”. Hence, the lines consist of orthographic projections of the intersections of the hull form with three mutually perpendicular sets of planes, drawn to a suitable scale. Figure 3.1 shows an example of lines drawing.

Figure 3.1: Example of lines plan



3.2.2 General Arrangement The general arrangement of a ship can be defined as the assignment of spaces for all the required functions and equipment, properly coordinated for location and access. The efficient operation of a ship depends upon the proper arrangement of each separate space and the most effective interrelationships among all spaces. It is important that the general arrangement be functionally and economically developed with respect to factors that affect both the construction and operation cost, especially the manpower required to operate the ship. Figure 3.2 shows an example of general arrangement.

Figure 3.2: Example of general arrangement



3.2.3 Scantling Drawing Scantling drawing is meant for the construction of the structures and plating of a ship during construction. The structure’s dimensions and the plate thickness is determined to withstand the load that is going to apply to the vessel during operation. Three locations of the structures are generally shown in the scantling drawing are midship, location of 25% from forward of perpendicular and location of 25% from aftward of perpendicular. An example of the scantling drawing is shown in Figure 3.3.

Figure 3.3: Sample of scantling drawing 3.2.4 Detail / Production Drawing Production drawing shows the details of the system onboard, the fabrication and assembly process of the system. An example of production drawing is shown in Figure 3.4.



Figure 3.4: Production drawing

3.3 IMPORTANCE OF SHIP DRAWINGS Ship drawings are important because they represent the unique hull shape of a ship. Every ship has its own design and hull shape. Ship drawings of a particular hull cannot be interchanged or share with another hull. Without ship drawings, modification, repair and maintenance work is hard to carry out. Ship drawings are used in all the design calculation and analysis. Without ship drawings, initial calculation and prediction of powering and performance of a vessel cannot be done. Ship drawings also considered as the basic data are to be used for the production process. Previous old shipyard build vessel based on experience, but when a new design of hull is being introduced, ship drawings are essential to make sure that the accuracy and requirement fulfilled for a vessel. Ship drawing is part of the contractual matters. Without ship drawing, a vessel cannot be classed. No classification society will approve and class a ship without the proper ship drawing. Among the various drawings in ship drawing, the most important and basic ship data is Lines Plan Drawing. Lines plan drawing represents the basic outer shape of a ship. Without lines plan drawing, all the other drawings cannot be drawn. In this short course, concentration and hands-on on lines plan drawing will be stressed.



Chapter 4 Introduction to Lines Plan 4.1 INTRODUCTION Ship has a complex and unique hull shape due to its double curvature and non-homogeneous cross sections. Unlike simple object like cylinder, box, and cone which can be represented in simple orthographic drawing, ship hull require special way of representing its unique and complex shape. Not only it require to be shown in three different orthogonal views, more lines are also needed in order to represents its shape at different cross sections or planes. For this reason, the ship hull drawing is always called as Lines Plan Drawing. Lines Plan is a lines drawing that represent the shape of the ship hull looking from three orthogonal (perpendicular to each other) views i.e. front, side and top views. The front view is termed as Body Plan, the side view is the Sheer Plan and the top view is the Half Breadth Plan. Since all of these views represent the same hull, they are interrelated to each other, thus the preparation of lines plan drawing must follow certain standard procedure. Lines plan drawing has always regarded by the naval architects as the most important piece of information about the ship. This is due to two reasons i.e. the ship performance and ship design process. On the performance of the ship, the shape of the hull form determines the power required to drive the ship, thus reflect the ship speed, its also determine the amount of pay load (capacity), comfort, habitability, etc. On the ship design process, lines plan drawing is the first information that needs to be made available. Without lines plan drawing, no calculation, design and analysis works can be performed. Construction process also can only be commenced after the lines plan drawing is completed. 4.2 TYPES OF HULL FORMS There are various types of hull form in ship design. Generally, it can be categorized into the following:

• Displacement hull (round bilge) • Planning Hull (Vee Hull with Hard Chine) • M hull • Catamaran • Yacht • Other Hull Types

Some samples of the various hull forms are shown in Figure 4.1 to 4.5.



Figure 4.1: Body plan of a displacement hull (Container Ship)

Figure 4.2: Body plan of a planning hull (Vee hull with hard chine)



Figure 4.3: Body plan of a catamaran

Figure 4.4: Body plan of a swath



Figure 4.5: Body plan of a yatch



4.3 BODY PLAN Body Plan represents the shape of the ship hull when viewing from the front or rear of the ship at every ship stations as shown in Figure 4.6. Station is a transverse cross-section along the ship length which normally equally spaced. The body plan concept can be better understood by referring to Figure 4.7. A ship is normally divided into 11 or 21 stations from after perpendicular, AP (Sometimes noted as station 0) until forward perpendicular, FP (or noted as station 10 0r 20). Half or even quarter station may also be used especially at the region with high curvature. Body plan is normally placed at the top right hand side of the drawing although it can also be placed at the middle or on top of the sheer plan drawing depending on the size and type of ship. Since most ships have symmetrical shape for both port (left side looking from rear) and starboard (right) sides, only one side is shown in the drawing. Therefore, it is almost a standard practice to show the stations of the rear region of the ship at the left side of body plan while the right hand side of the body plan represents the stations at the forward region of the ship. The curve on the body plan is also call station curve. The centre line of the body plan represents the centre line of the ship. Apart from showing the station curves, the body plan also shows the waterlines and the buttock lines grid. These grid lines are essential not only for reference lines but also used for transferring and checking data from one plan to another.

Figure 4.6: Body plan



Figure 4.7: 3-Dimensional body plan 4.4 HALF BREADTH PLAN The same hull form if it is viewed from top will produce the plan view of the ship. However since the hull shape is complex and unique, the plan view must be made at several waterline planes. Thus Half Breadth Plan is a lines drawing that represents the shape of the ship hull looking from top view at every waterlines of the ship. Waterline is the horizontal plane that cut the ship along its vertical axis, thus creating the waterlines curves as shown in Figure 4.8. Waterline is normally equally spaced, although half waterline may also be used at the lower region of the ship. Since the hull is symmetry about its centre line, only half of the hull is shown in this plan as shown in Figure 4.9 Apart from waterline curves, the deck line curve needs to be drawn on this plan. If the ship has bulwark, chines or / and knuckles lines, these curves have also to be shown in the drawing. In this plan, the grid lines shown are the stations and buttock lines of the ship.



Figure 4.8: 3-Dimensional half-breadth plan

Figure 4.9: Half breadth plan



4.5 PROFILE / SHEER PLAN Sheer Plan which is usually placed at the top left hand side of the lines plan drawing represent the shape of the ship hull looking from the side of ship at several buttock lines. Buttock line is the vertical plane that cuts the ship along its length, creating the buttock line curves as indicated in Figure 4.10. The middle buttock line (normally labeled as BL 0) is the plane that cuts the ship along its centre line which creates the profile curve of the ship. Other buttock lines are drawn outward (offsets) of ship’s centre line and normally at equally spaced distance. The stations and waterlines grids are shown in this sheer plan drawing. A typical sheer plan drawing is shown in Figure 4.11.

Figure 4.10: 3-Dimensional sheer plan

Plan B = Plan C



Figure 4.11: Profile / Sheer Plan 4.6 OFFSETS DATA Offsets data is the data that is extracted (measured) from the lines plan drawing and considered the most important data for the design, calculation, analysis and construction of the ship. As the name implied, Offset Data is the distance measured from the centre line of the ship to the specific point on the curves (station or waterline curves). The offset data must be measured at every intersection points on each stations and waterlines including deck line, chines, knuckles and bulwarks (if any). Offset data also called as half breadth data, because it represents the half breadth of the ship at every station and waterlines. A typical example of offsets data is shown in Table 4.1 and the measurement of offsets data is illustrated in Figure 4.12. In the offsets Table, it is also a standard practice to indicate the data of height above based for deck, chine, bulwark, and knuckles lines. The height above base of buttock lines may also be included whenever necessary. A sample of the complete lines plan drawing containing the body plan, profile, half-breadth plan and offset are shown in Figure 4.12.

Table 4.1: Offsets table



Figure 4.12: Offset data relation to lines plan



4.7 DRAWING QUALITY The quality of the ship lines plan drawing is judged based on the following criteria; Completeness – The drawing must include all plans (body plan, half breadth plan and sheer plan) and necessary information such as Title block, Main dimension and Ship Particulars, and Offsets Table. A complete drawing means that the user can find all the necessary information from the drawing without the need to seek from other sources. Accuracy – The drawing must accurately represent the ship hull form. Thus the main dimensions and the offset data must be accurately represented by the lines plan drawing. Cross checking on every plan is often necessary in order to check the accuracy of the hull being drawn. Smooth and Fair – All lines or curves drawn must be smooth and fair. Smoothness is defined as no sudden or abrupt changes of the curve slope (gradient) unless it is meant for (knuckles, chine lines). Fairness can be interpreted in various ways. The simplest definition of fairness is curve with no unnecessary inflexion points or waviness. Drawing and judging smoothness and fairness of ship curves required skill and experience but it is an essential criteria for a good drawing, hence good ship geometry. Labeling – All curves and important information on the drawing must be labeled clearly and appropriately. These should include, plans title, station no, waterlines no and buttock lines no. The size and location of the labeling must also suitable with the drawing size. Ship Main Dimensions and Particulars – The main dimension of the ship including Length Overall, Length Between Perpendiculars, Breadth Moulded, Depth Moulded and Draft must be shown in the drawing. Other ship particulars such ship name, type, capacity, speed may also be included. This information should be written in a box, normally placed above the title block. Title Block – Information regarding company’s name, ship name, project title, drawing title, drawing number, date, scale, designer’s and draftsman’s name, date of latest modification and other relevant information should be shown in the title block. Title block should be located at the bottom right hand corner of the drawing paper. An example of a title block is shown in Figure 4.13. Drawing Layout – Margin lines / border lines of a 20 – 30mm distant from the drawing paper edges should be drawn first. All plans, main dimensions block, title block and offsets table should be arrange properly as to occupy the entire area of the drawing paper. Thus proper scaling and clearance must be decided first before starting the drawing works.



Figure 4.13: Example of a title block



Chapter 5 Lines Plan Drawing Hands-On 5.1 INTRODUCTION Drawing lines plan normally begins with the reading of the data from the offset tables. This is followed by drawing the grid lines that form the body plan, sheer plan and half-breadth plan. Lines that represent the shape of the vessel must be smooth and fair. Beside smoothness and fairness, accuracy is also very important, that is measurements at every line must match in all the three different views. Choosing the right scale is also essential task in the drawing of lines plan. Scale that is too small will lead to larger error on the mistake and inaccurate on the lines that were drawn. On the other hand scale that is too large requires large drawing paper and may beyond the size of the drawing equipments. 5.2 UNDERSTANDING OFFSET TABLE Offset table and lines plan has the same purpose of existence: give the correct perspective of a vessel to viewer. However, both work in a different manner. Offset table shows the measurement of a vessel for calculation purposes as well as preparation of lines plan, whereby lines plan makes sure that the measurement from the offset table are able to produce a smooth and fair hull form. In the offset table, measurements are for outlining the shape of a vessel like deck, keel, water lines, and buttock lines. The location of stations, base line and centre line are often used for the references of the measurement that is being taken. The recorded measurements are in two formats: height and half-breadth. Height is normally referring to the baseline of the ship and half-breadth is referring to centre line of the ship.



5.3 LINES PLAN DRAWING PROCEDURES Each participant will be given the ship main particulars and offset data. The Lines Plan Drawing shall be drawn from the existing offsets data. Following are the steps to be taken as a guideline for the drawing hands on task.

STEP TASK

1

Preparation of Data and Drawing Equipment

Main Dimension and Offsets Data must be made available Drawing equipment :-

- Drawing Table (with rotating and adjustable arms) - Drawing Paper (A0 or A1 size of good quality paper / tracing paper) - Ship Curves (sets of various shapes and sizes) - Battern / Spline - Weight Duck - Scale Ruler (with Metric Scale) - Eraser and Soft cloth - Mechanical Pencils (0.5mm, 0.3mm, H, HB and 2B) or Pen (0.35mm,0.5mm)

2

Determination of Drawing Scale and Layout

Based on the main dimension and the drawing paper determine appropriate drawing scale. These values have to be determined based on ship length and the distance / clearance between plans. Use appropriate scale and size. The space for title block, main dimension and offsets table must be given consideration as to ensure the effective use of the drawing paper.

3

Drawing of Main Boxes and Grid Lines

Draw the main boxes and grid lines for all three plans (i.e. station, waterlines and buttock lines grid). The grid lines must be drawn based on the station and waterline spacing. Arrange these boxes such that clearance between them is balance. Label these lines accordingly.

4

Draw Body Plan

Select one station (it is good practice to start from midship station). For this station mark the offset data on each waterline on the body plan grid. Using ship curve draw a station curve by connecting these offsets mark. Make sure the curve drawn is smooth and fair. Repeat this step for other stations. Label the station number accordingly. Now your body plan is almost completed.

5

Draw Profile Curve

On the sheer plan grid, draw the profile of the ship based on the profile of the basis ship. The profile coordinates is to be measured from the basis ship profile. Make sure that the measurement is taken using the appropriate scale.

6 Draw Half Breadth Plan



To draw the half breadth plan, you need to use a clean sheet of white paper A4 size. Mark the offsets data from body plan at a selected waterline on the edge of this paper. Bring the offsets mark on to the half breadth plan grid and mark it on appropriate stations. The point at both end (fwd and aft) shall be determined by projecting the intersection points between waterline and profile at sheer plan drawing (as in step 5) to the half breadth plan at centre line. Draw a smooth and fair waterline curve by connecting all the marked points using weight and batten. Repeat this step for other waterlines. Special care must be taken for the transom station (if any). Label the waterlines number accordingly. Your half breadth plan is almost completed.

7

Draw Sheer Plan

The sheer plan shall be drawn based on the completed body plan and half breadth plan drawings. First, draw buttock lines (at least 3 buttock lines) on both body plan (both sides) and half breadth plan. On the body plan drawing, mark the intersection points between the selected buttock line grid and the station curves. Draw a horizontal line from these points to the corresponding stations grid on the sheer plan and mark the intersection points accordingly. Next, on the half breadth plan, mark the intersection points between the selected buttock lines grid (as in body plan) and the waterlines curves. Draw a vertical line from these points to the corresponding waterlines grid on the sheer plan and mark accordingly. The buttock line curve is drawn by connecting all the intersection marks either on the stations or waterlines grids. Make sure the curve drawn is smooth and fair. Repeat the above step for other buttock lines.

8

Cross Checking and Fairing Process

While drawing the buttock lines curves, you may have to move/shift some of the intersection points in order to draw a smooth and fair curve. In doing so, it is essential to understand that any movement of point on a particular plan will eventually changed the position of the corresponding points on the other two plans. Therefore it is desirable to do cross check all plans whenever any points need to be shifted. Special care must be given and the movement of the point must be done simultaneously on all plans. Significant changes will eventually lead to drawing a new curve on all plans. This process is called fairing process and may required to be carried out many times before a fair hull form be able to be generated. Up to this point you have almost completed the lines plan drawing but the quality of your drawing depends very much on the skill and experience. Practices make perfect.

9

Draw Offsets Table and Main Dimensions

Draw the Offsets Table and Main Dimensions of the ship on the appropriate location. Offsets table must include the half breadth data for all station at every waterline including deck and bulwark (if any). The height above base for the deck, bulwark and chine lines (if any) for every station must also be indicated on the offsets table. The main dimension should at least include Length Overall, Length Between Perpendiculars, Moulded Breadth, Moulded Depth, and Draft (if known).

10

Draw Title Block

Complete the lines plan drawing by preparing the title block which at least indicates the name and company logo, name of the ship, drawing number, drawing title, scale, date, and initial of designer, draftsman, and checker. Please refer to the standard format.



Chapter 6 Obtaining Offset Data From a Boat 6.1 INTRODUCTION Traditional boats have been built without the use of scientific calculations or any plan or drawings. Although it safety and suitability is not known with certainty, the boats have been accepted for used for a long time. In some cases the boats have special characteristics which are better than boats which are designed scientifically. This results from a long process of development of skill and modification through out a number of generations.

To ensure that the good traditional designs are not lost, detail measurements of these boats must be recorded systematically so that the good characteristics can be studied. Such record is also important and will bring benefit to future generation.

For a designer or builder, the measurements of traditional boats could be a useful reference. By comparing the various measurement and drawings of the traditional boats, they can design and build better boats. This is because the reference boats are proven in terms of performance.

For naval architects or engineer, the drawings can be a basis for calculations of stability, tonnage, powering etc. Moreover through research, characteristic of optimal boats can be obtained.

In this Chapter a method to measure and obtain offset data from a boat will be presented. Using this offset data the lines plan of the boat can be drawn and the associated calculations can be carried out.

6.2 A METHOD TO MEASURE HULL OF A BOAT The boat to be measured must be on dry land either in the dock or on berth. In this position the keel must be level as shown in Figure 1. To facilitate measurements, a number of reference lines must be determined:

i) The keel line is taken as the base line. ii) Forward perpendicular and aft perpendicular are marked. iii) The distance between the forward and aft perpendiculars is divided into eight or

ten parts. These stations need not be necessarily of similar length but preferably so. The location of this reference lines are shown in Figure 1.



Figure 6.1: Position of Boat Onshore 6.3 MEASURING THE STEM AND STERN OF THE BOAT Measuring the stem and stern can be done in two ways:

i) Using a pole as a vertical reference line and measuring horizontal distance between the stem or stern and the vertical reference line. This is shown in Figure 2. To ensure the accuracy of the measurement, the vertical reference line must be guided by plumb and line. The horizontal measurement is leveled using a spirit level. Table 1 shows an example of offset table obtain through this method.

ii) Radial method shown in Figure 3. In this method two or three reference positions A, B and C are chosen. The locations of points 1, 2 and 3 are determined by measuring its distance from A, B and C. Table 2 shows an example of offsets obtained in this manner.

From the offset table obtained as above, the shape of the stem and stern can be drawn using a suitable scale.



Figure 6.2: Measuring Stern and Bow Profile Using Method (a)

Table 6.1: Offset Table for Bow [Method (a)]

Point Height Above Baseline Distance from Pole 1 Z1 X1

2 Z2 X2

3 Z3 X3



Figure 6.3: Measuring stern and Bow Profile Using [Method (b)]

Table 6.2: Offset Table for Bow [Method (b)]

Point A B C

Distance

1 J1a J1b J1c

2 J2a J2b J2c

3 J3a J3b J3c



6.4 MEASURING THE HULL OF THE BOAT Method (a) and (b) used for measuring stem and stern can be used to measure the shape of the hull. Figure 4 shows how such methods can be used.

Figure 6.4: Measuring Section Shape Using Method (a) and (b)

smk4532 ship design ii - universiti teknologi malaysiakoh/smk4532/lecturenotes.pdf · smk4532 ship...

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