Topic-1 MAIN DIMENSIONS

Basic design of the Ship

The main dimensions of the barge influence many of the ship’s characteristics such as stability, carrying capacity, power requirements and its economic efficiency. So, they should be coordinated such that the vessel satisfies the design conditions as well as the characteristics desired by the shipping companies with various combinations of dimensions. The owner requires a vessel which will give him the best possible returns for his initial investment and operating costs. Basic design includes selection of main dimensions, hull form, power, and type of generator, preliminary arrangement of tanks and machinery, and major structural arrangements. Proper selections assure the attainment of the mission requirements such as carrying capacity and deadweight. It includes checks and modifications for achievement of required carrying capacity, subdivision of tanks and stability standards, freeboard and tonnage measurement. 

    Length (L)

The length of the ship is measured from the extreme forward end to the aftermost point of the stern. The length, L, shall be taken as 96 percent of the total length, in meters (feet), on a waterline at 85 percent of the least molded depth, D. In barges designed with a rake of keel, the waterline on which this length is measured shall be parallel to the designed waterline.

 Breadth (B)

The breadth of a ship is its width at the widest point as measured at the ship's nominal waterline. It is measured in meters.

    Depth (D)

Depth is defined as the height of the ship at the midship section from the base line to the molded line of the deck at side.

      Draught (T)

The draught of a ship's hull is the vertical distance between the waterline and the bottom of the hull (keel), with the thickness of the hull included. Draught determines the minimum depth of water a ship or boat can safely navigate. The draught, T, is the molded draught, in meters (feet), from the molded baseline to the summer load line.

Topic - 11 Damage stability (Stability in the damaged condition)

Damage stability calculations are much more complicated than intact stability. Software utilizing numerical methods is typically employed because the areas and volumes can quickly become tedious and long to compute using other methods.

The loss of stability from flooding may be due in part to the free surface effect. Water accumulating in the hull usually drains to the bilges, lowering the centre of gravity and actually decreasing (It should read as increasing, since water will add as a bottom weight thereby increasing GM) the Meta centric height. This assumes the ship remains stationary and upright. However, once the ship is inclined to any degree (a wave strikes it for example), the fluid in the bilge moves to the low side. This results in a list.

Ø  Floodable Length: The floodable length at any point within the length of the ship is the maximum portion of the length, having its center at the point which can be symmetrically flooded at the prescribed permeability, without immersing the margin line.

Floodable length (in short) is the length of (part of) the ship that could be flooded without loss of the ship.

Ø  Determination of Floodable length is essential to determine

1. How many watertight compartments (bulkheads) are needed
2. Factor of subdivision (How many water compartments flooded without loss of ship)

Topic - 12 Stability systems

The stability systems are classified as
1.1.1        Passive systems

1.      Bilge keel: A bilge keel is a long fin of metal, often in a "V" shape, welded along the length of the ship at the turn of the bilge. Bilge keels are employed in pairs (one for each side of the ship). A ship may have more than one bilge keel per side, but this is rare. Bilge keels increase the hydrodynamic resistance when a vessel rolls, thus limiting the amount of roll a vessel has to endure.

2.      Outriggers: Outriggers may be employed on certain vessels to reduce rolling. Rolling is reduced either by the force required to submerge buoyant floats or by hydrodynamic foils.

3.      Antiroll tanks: Antiroll Tanks are tanks within the vessel fitted with baffles intended to slow the rate of water transfer from the port side of the tank to the starboard side. The tank is designed such that a larger amount of water is trapped on the higher side of the vessel. This is intended to have an effect completely opposite to that of the free surface effect.

4.      Para vanes: Para vanes may be employed by slow-moving vessels (such as fishing vessels) to reduce roll.

1.1.2        Active systems

Active stability systems are defined by the need to input energy to the system in the form of a pump, hydraulic piston, or electric actuator. These systems include stabilizer fins attached to the side of the vessel or tanks in which fluid is pumped around to counteract the motion of the vessel.
1.      Stabilizer fins: Active fin stabilizers are normally used to reduce the roll that a vessel experiences while underway or, more recently, while at rest. The fins extend beyond the hull of the vessel below the waterline and alter their angle of attack depending upon heel angle and rate-of-roll of the vessel.
 2.      Gyroscopic internal stabilizers: Gyroscopes were used to control a ship's roll. Gyro stabilizers consist of a spinning flywheel and gyroscopic precession that imposes boat-righting torque on the hull structure. A gyroscope has three axes: a spin axis, an input axis, and an output axis. The spin axis is the axis about which the flywheel is spinning and is vertical for a boat gyro. The input axis is the axis about which input torques is applied. The principal output axis is the transverse (athwart ship) axis about which the gyro rotates in reaction to an input.

Topic- 13 Stability Considerations

      1. Crane Outreach

When using cranes and other lifting gear such as A frames that are barge mounted, it must be noted that the weight of the lifted load acts at the point of suspension – not at the base of the crane. The overturning moment on the barge, tending to cause it to capsize, is the product of the weight of the lifted load, and the (horizontal) distance of the point of suspension from the centre of buoyancy.

The greatest uplift or detachment force, acts at the point of attachment (of the crane to the barge) furthest from the point of suspension. This is the force tending to turn the crane over and the moment of this force is the product of the weight of the lifted load, and the (horizontal) distance of the point of suspension from the point of uplift.

 2. Free surface effect

Fluids such as fuel and water can adversely affect the stability of a moving vessel. A shallow covering of water over a large enclosed deck can cause a significant problem. 150 mm of fresh water covering a 24 m by 6 m deck weighs 21.6 tonne, and as the vessel rolls this weight will be transferred outboard to the down side of the roll. Sloshing is another phenomenon, which can greatly amplify the destabilizing effect of a large free surface of fluid. The effect of sloshing is worst if the movement of fluid coincides with the movement of the vessel. Baffles are used to break up the free surface within a tank and to prevent sloshing.

3. Shifting Cargo

Securing arrangements should be of such design that they are strong enough to prevent any cargo movement during transit. Maritime Rule part 24B gives prescribed requirements for stowage and securing of all cargoes.

       4. Loading and Discharge

It is vital that stability is considered during all phases of barge operations, including loading and discharge. The stability conditions during loading and discharge are often quite different from those when fully loaded. High loads, moving loads, and off–centerline loading plans all need special consideration. A low initial GM value, a combined KG that is close to or below the required minimum and small righting areas all mean that the loaded barge will have poor recovery characteristics when rolling in a seaway.

Topic - 17 Fore End Construction

Framing

1.      Deck Longitudinals

Each deck longitudinal, in association with the plating to which it is attached, is to have a section modulus SM not less than that obtained from the following equation:

SM_req = 7.8chsl² cm³                    (3-2-5/3.1)

                                                 = 102.4 cm³

   Minimum depth obtained from Rule book = 165.67mm

   Depth considered = 357.19mm = 14 1/16 in.

   Web thickness = 3/4 in.

   Flange thickness = 1 5/16 in.

   Flange width = 14 in.

                                         SM_obtained = 560.2 cm³

2.       Deck Transverses

Each deck transverse, in association with the plating to which it is attached, is to have a section modulus SM not less than that obtained from the following equation:

SM_req = 4.74chsl² cm³            (3-2-5/3.3)

                                                                                    = 62.22 cm³          

     Minimum depth obtained from Rule book = 236.472mm

     Depth considered = 357.19mm = 14 1/16 in.

     Web thickness = 3/4 in.

     Flange thickness = 1 5/16 in.

     Flange width = 14 in.

                                         SM_obtained = 560.2 cm³

3.       Bottom and Side Longitudinals

Each bottom and side longitudinal, in association with the plating to which it is attached, is to have a section modulus SM not less than that obtained from the following equation:

SM = 7.8chsl² cm³                      SM = 0.0041chsl² in³           (3-2-5/3.5)

 SM (bottom Longitudinals) = 59.349cm³ 

 SM (side Longitudinals)      = 55.362 cm³

Minimum depth obtained from Rule book (for both bottom and side) = 354mm

Depth considered = 357.19mm = 14 1/16 in.

Web thickness = 3/4 in.

Flange thickness = 1 5/16 in.

Flange width = 14 in.

                                         SM_obtained = 560.2 cm³

4.       Bottom and Side Transverses

Each bottom and side transverse, in association with the plating to which it is attached, is to have a section modulus SM not less than that obtained from the following equation:

SM = 4.74chsl² cm³                         SM = 0.0025chsl² in³       (3-2-5/3.7)

SM (bottom and side Longitudinals) = 47.10 cm³ 

     Minimum depth obtained from Rule book for side transverses = 354mm

     Depth considered = 357.19mm = 14 1/16 in.

     Web thickness = 3/4 in.

     Flange thickness = 1 5/16 in.

     Flange width = 14 in.

                                         SM_obtained = 560.2 cm³

      Minimum depth obtained from Rule book for bottom transverses = 441.79mm

     Depth considered = 17 7/6 in. = 442.91mm

     Web thickness = 1 in.

     Flange thickness = 1 3/4 in.

     Flange width = 15 7/8 in.

                                         SM_obtained = 1333.33 cm³

  

5.       Proportions

Deck and bottom chords and transverses and side transverses are to have proportions complying with the following:

Ø  Deck chords and transverses are to have a depth of not less than 83.5 mm per meter of span l (1 in. per foot of span l).

Depth = 236.472 mm

Finalized Depth = 14 1/16 in = 357.19mm

Ø  Side transverses are to have a depth of not less than 125 mm per meter of span l (1.5 in. per foot of span l).                             

                                                    Side transverses depth =354 mm

Finalized Depth = 14 1/16 in. = 357.19 mm

Ø  Bottom transverses and chords are to have a depth of not less than 156 mm per meter of span       l (1.875 in. per foot of span l).

Bottom transverse depth =441.79 mm

Finalized Depth = 17 7/16 in. = 442.91 mm

STRUCTURAL PARTS OF THE HULL

The hull is the main body of the ship below the main outside deck. The hull consists of an outside covering (or skin) and an inside framework to which the skin is secured. The skin and framework are usually made of steel and secured by welding. However, there may still be some areas where rivets are used. The steel skin may also be called shell plating.

The main centerline structural part of the hull is the keel, which runs from the stem at the bow to the sternpost at the stern. The keel is the backbone of the ship. To the keel are fastened the frames, which run athwartship. These are the ribs of the ship and gives shape and strength to the hull. Deck beams and bulkheads support the decks and gives added strength to resist the pressure of the water on the sides of the hull.

SKIN

The skin, or shell plating, provides water-tightness. The plates, the principal strength members of a ship, have various thickness. The heaviest plates are put on amidships. The others are put on so that they taper toward both ends of the ship (from the keel toward the bilge and from the bilge toward the upper row of plates). Using plates of various thickness reduces the weight of the metal used and gives the vessel additional strength at its broadest part. The plates, put on in rows from bow to stern, are called strakes. They are lettered consecutively, beginning at the keel and going upward.

STRAKE NAMES

The bottom row of strakes on either side of the keel, are called garboard strakes. The strakes at the turn of the hull, running in the bilge, are bilge strakes. The strakes running between the garboard and bilge strakes are called bottom strakes and the topmost strakes of the hull are sheer strakes. The upper edge of the sheer strake is the gunwale.

BULKHEADS

The interior of the ship is divided by the bulkheads and decks into watertight compartments. A vessel could be made virtually unsinkable if it were divided into enough small compartments. However, too many compartments would interfere with the arrangement of mechanical equipment and the operation of the ship. Engine rooms must be large enough to accommodate bulky machinery. Cargo spaces must be large enough to hold large equipment and containers.

ENGINE ROOM

 The engine room is a separate compartment containing the propulsion machinery of the vessel. Depending on the size and type of propulsion machinery, other vessel machinery may be located there (such as generators, pumping systems, evaporators, and condensers for making fresh water). The propulsion unit for vessels is a main engine. The "shaft" or rod that transmits power from the engine to the propeller leads from the aft end of the engine to the propeller.

EXTERNAL PARTS OF THE HULL

The waterline is the water-level line on the hull when afloat. The vertical distance from the waterline to the edge of the lowest outside deck is called the freeboard. The vertical distance from the waterline to the bottom of the keel is called the draft. The waterline, draft, and freeboard will change with the weight of the cargo and provisions carried by the ship. The draft of the ship is measured in feet and inches. Numbered scales are painted on the side of the ship at the bow and stern.
The relationship between the drafts at the bow and stern is the trim. When a ship is properly balanced fore and aft, she is in trim. When a ship is drawing more water forward than aft, she is down by the head. If the stern is too far down in the water, she is down by the stern. If the vessel is out of balance laterally or athwartship (leaning to one side) she has a list. She may be listing to starboard or listing to port. Both trim and list can be adjusted by shifting the weight of the cargo or transferring the ship’s fuel and water from one tank to another in various parts of the hull.
The part of the bow structure above the waterline is the prow. The general area in the forward part of the ship is the forecastle. Along the edges of the weather deck from bow to stern are removable stanchions and light wire ropes, called life lines. Extensions of the shell plating above the deck are called bulwarks. The small drains on the deck are scuppers. The uppermost deck running from the bow to the stern is called the weather deck. The main deck area over the stern is called the fantail or poop deck. The flat part of the bottom of the ship is called the bilge. The curved section where the bottom meets the side is called the turn of the bilge.
Below the waterline are the propellers or screws which drive the ship through the water. The propellers are attached to and are turned by the propeller shafts. A ship with only one propeller is called a single-screw ship. Ships with two propellers are called twin-screw ships. On some ships (especially landing craft) there may be metal frames built around the propellers (called propeller guards) to protect them from damage. The rudder is used to steer the ship.

NAMES OF DECKS

The decks aboard ship are the same as the floors in a house. The main deck is the first continuous watertight deck that runs from the bow to the stern. In many instances, the weather deck and the main deck may be one and the same. Any partial deck above the main deck is named according to its location on the ship. At the bow it is called a forecastle deck, amidships it is an upper deck, and at the stern it is called the poop deck. The term weather deck includes all parts of the forecastle, main, upper, and poop decks exposed to the weather. Any structure built above the weather deck is called superstructure.

SHIPBOARD DIRECTIONS AND LOCATIONS

Bow

The front end of the ship is the bow. When you move toward the bow, you are going forward, when the vessel is moving forward, it is going ahead. When facing toward the bow, the front-right side is the starboard bow and the front-left side is the port bow.

Amidships (Center)

The central or middle area of a ship is amidships. The right center side is the starboard beam and the left center side is the port beam.

Stern (Back)

The rear of a vessel is the stern. When you move in that direction you are going aft, when the ship moves in that direction it is going astern. When looking forward, the right-rear section is called the starboard quarter and the left-rear section is called the port quarter.

Other Terms of Location and Direction

The entire right side of a vessel from bow to stern is the starboard side and the left side is the port side. A line, or anything else, running parallel to the longitudinal axis or centerline of the vessel is said to be fore and aft and its counterpart, running from side to side, is athwartships.

From the centerline of the ship toward either port or starboard side is outboard and from either side toward the centerline is inboard. However, there is a variation in the use of outboard and inboard when a ship is on berth (moored to a pier). The side against the pier is referred to as being inboard; the side away from the pier as outboard.

STERN ARRANGEMENT

• THE UPPER PART OF THE STERN OF A SHIP EXTENDS ABAFT THE RUDDER POST, & THERE MUST BE A SPECIAL ARRANGEMENT OF FRAMING TO SUPPORT IT.
• THIS FRAMING IS MAINLY CARRIED BY THE ‘TRANSOM’, WHICH CONSISTS OF A DEEP, HEAVY FLOOR, SECURELY ATTACHED TO THE RUDDER POST, IN ASSOCIATION WITH A TRANSVERSE FRAME & BEAM. THESE ARE KNOWN AS THE ‘TRANSOM FLOOR’ & ‘TRANSVERSE BEAM’.
• THE TRANSOM FLOOR MUST HAVE THE SAME DEPTH AS THE FLOORS IN THE CELLULAR DB, BUT MUST BE SLIGHTLY THICKER.

• ORDINARY STERNS:

• THESE WERE OFTEN CALLED ‘COUNTER’, OR ‘ELLIPTICAL’ STERNS.
• INSTEAD OF THEM, CRUISER OR TRANSOM STERNS ARE USED.

• CRUISER STERNS:

• THEY HAVEA SYSTEM OF ORDINARY TRANSVERSE FRAMING WHICH IS SUPPORTED BY AN INTERCOASTAL GIRDER AT THE CENTRE LINE.
• THE GIRDER HAS TO BE DOUBLED, JUST ABAFT THE TRANSOM FLOOR, TO ALLOW THE RUDDER STOCK TO PASS.
• A NUMBER OF CANT FRAMES ARE FITTED ABAFT THE AFTERMOST TRANSVERSE FRAME.
• THE FRAMES ARE TO BE OF THE SAME SIZE AS BULB ANGLE FRAMES IN PEAKS & ARE TO EXTEND TO THE STRENGTH DECK.
• THE FRAME SPACING IS NOT TO EXCEED 610 mm.
• WHERE EXTRA STRENGTH IS REQUIRED, WEB FRAMES MAY BE REQUIRED & ALSO EXTRA LONGITUDINAL GIRDERS TO SUPPORT THEM.

TRANSOM STERN:

• THIS IS SIMILAR TO A CRUISER STERN, EXCEPT THAT THE CANT FRAMING AT THE AFTER END IS OMMITED & IS REPLACED BY A FLAT PLATE, CALLED A TRANSOM.

RUDDER TRUNK

• THIS IS OFTEN FORMED BY CARRYING -UP THE DOUBLED CENTRE GIRDER TO THE DECK ABOVE IN THE FORM OF A BOX.

BEAMS & FRAMES

BEAMS

Usually of offset bulb or inverted angle section, placed athwart ships.

•  Deck beams are required to support the deck & any loads it carries
•  Deck beams act as struts assisting in holding the sides of the ship apart against the inward pressure of the sea.

FRAMES

Usually of offset bulb or inverted angle section, placed on side shell.

•  Scantlings of transverse frames increase with depth & spacing.
•  Transverse frames may be numbered from aft to for’d.
•  Frames are required to support the shell plating

TYPES OF FRAMES

1. TRANSVERSE FRAMES
2. LONGITUDINAL FRAMES
3. WEB FRAMES

BULKHEADS

• Vertical partitions in a ship arranged transversely are referred to as bulkheads.
•  The bulkheads subdivide the ship into a no. of watertight compartments.
•  They give large structural support, resist any tendency to deformation (racking stresses) & assist in spreading the hull stresses over a large area.
• All ships are to have a Collision bulkhead, situated <0.05L & >0.08L for cargo ships (.05L + 3 m for passenger ships).
•  All ships are to have an after peak bulkhead enclosing the stern tube in a w-t compartment.
•  All ships are to have a bulkhead at each end of the machinery space.
•  Additional w-t bulkheads are to be fitted in cargo ships depending on the length of the ship.

SHIPBOARD MEASUREMENTS

A ship’s size and capacity can be described in two ways--linear dimensions or tonnages. Each is completely different yet interrelated.

A ship’s measurement is expressed in feet and inches--linear dimensions. A ship is a three dimensional structure having length, width, and depth.

A Ship’s Dimensions

Draft - The depth of a ship in the water. This vertical distance is measured from the bottom of the ship to the surface of the water. Draft marks are cut into or welded on the surface of a ship’s plating. They are placed forward and aft on both sides of the hull and also amidships. At the midships draft we will also find the authorized Load Line markings which designate maximum drafts allowed for vessels under various conditions.

Freeboard - The vertical distance from the water line to the top of the weather deck on the side.

FREEBOARD

Freeboard is the distance between the waterline and the freeboard deck at mid length. The freeboard deck is the uppermost continuous deck which has means of closing all openings. Rules allow different freeboards for different ships in relation to their construction and cargo they carry. There are two types of ship;

Type A -which covers vessels designed to carry only liquid cargoes.

Type B-Which covers all other types of ship,

For type A ships cargo tanks must only have small openings which can be effectively sealed

Type B ships must have sufficient bulkheads and sealing arrangements for openings, but such openings e.g. hatches can be large

The freeboard allowed will be smaller for the type A ship compared to the type B ship of similar length because of the type of cargo carried and means of access for water. Type B ships classed as B-60 may have their freeboard reduced by 60% of that required for a normal B-100 ship provided that its method of construction approaches that of the type A ship. This type exists with OBO's. 

TONNAGE MEASUREMENT

GROSS TONNAGE:

1. IT IS A MEASURE OF SHIP’S CUBIC CAPACITY
2. IT IS EXPRESSED IN TERMS OF 1 TON/100 CU FT., OR 1 TON/3M_­³ OF SPACE
3. GRT CONSISTS OF ALL ENCLOSED SPACES WITH CERTAIN EXCLUSIONS

GRT IS MADE OF SUM OF FOLLOWING:

• TOTAL VOLUME BELOW TONNAGE DECK
• CU. CAPACITY OF ALL SPACES IN T.D.
• CU. CAPACITY OF ALL ENCLOSED SPACES ON OR ABOVE UPPER DECK WITH CERTAIN EXCEPTIONS
• EXCESS HATCHWAYS IN EXCESS OF ½ % OF SUM OF a+b+c ABOVE

EXCLUDED SPACES

• TANKS USED EXCLUSIVELY FOR BALLAST.
• SPACES USED EXCLUSIVELY FOR MACHINARY SPACES FOR CREW & OFFICERS.
• WASHING & SANITARY SPACES FOR CREW & OFFICERS
• SPACES USED FOR NAVIGATION, RADIO ROOM, STORAGE FOR BATTERIES, CHAIN LOCKER

The gross tonnage (GT) of a ship shall be determined by the following formula:

GT = K₁*V

            Where: V = Total volume of all enclosed spaces of the ship in cubic meters,

                        K₁ = 0.2 + 0.02 log ₁₀ V

NET TONNAGE:

1. IT IS FOUND BY MAKING DEDUCTIONS FROM GRT
2. IT MAY BE DESCRIBED AS MEASURE OF EARNING CAPACITY OF THE SHIP
3. ALLOWANCE IS MADE FOR PROPELLING POWER
4. MASTER’S & CREW’S ACCOMMODATION INCLUDING WASH ROOM
5. WATER BALLAST SPACES OTHER THAN DOUBLE BOTTOM TANKS
6. SPACES USED FOR NAVIGATION, RADIO ROOM, & STORAGE SPACE FOR BATTERIES & SAFETY EQUIPMENT
7. CHAIN LOCKER
8. WHEN CARGO IS CARRIED BY FOREIGN GOING SHIPS IT IS MEASURED AND ADDED TO NRT

The net tonnage (NT) of a ship shall be determined by the following formula:

NT = K₂ * Vc * (4d / 3D) 2 + K₃ * [N₁ + N₂ / 10]

Vc = total volume of cargo spaces in cubic metres,

K₂ = 0.2 + 0.02 log ₁₀ V

K₃ = 1.25

D = moulded depth amidships in metres

d = moulded draught amidships in metres

N₁ = number of passengers in cabins with not more than 8 berths,

N₂ = number of other passengers,

K2 * Vc * (4d / 3D) 2 Shall not be taken less than 0.25GT

NT Shall not be taken less than 0.30GT