Naval Architecture: ship construction

Showing posts with label ship construction. Show all posts

Saturday, 14 January 2017

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)

=62.22cm³

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 = 0.0041chsl²in³(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 = 4.74chsl²cm³SM = 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

Tuesday, 28 July 2015

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

TRANSVERSE FRAMES
LONGITUDINAL FRAMES
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.

Monday, 27 July 2015

LOADLINES OF SHIPS

The following diagram shows the port and starboard side loadlines of a cargo ship. To see the port side loadlines, cover up the the right l/3 of the sketch. To see the starboard side loadlines, cover up

the left 1/3 of the sketch. The WNA loadline has been included in dotted lines as it is only required by vessels less than l00 metres in length, trading in the North Atlantic during the winter season. The exact limits and dates of the winter zone in the North Atlantic are given in the loadline rules.

All the lines are 25 mm thick, are cut into the shell plating and are painted white or yellow on a

dark background or black on a light background. The upper edge of each loadline indicates its exact level.

The top of the deck line indicates where the top of the freeboard deck would meet the outer side of the shell plating, if produced. Directly below the deck line is the Plimsoll mark (or loadline disc) and

the vertical distance between them is called the Statutory Summer Freeboard. The centre of the loadline disc is at the middle of the upper edge of its 25 mm thick, painted, diametric line. lhe deck line and the Plimsoll mark are situated exactly amidships.

Exactly 540 mm forward of the disc is a vertical line 25mm thick with horizontal lines, measuring 230 mm x 25 mm, on each side of it. On its forward side the lines are marked S, T and W (also WNA if applicable). The lines on the after side are marked F and TF.

The upper edge of the line marked S is in line with the horizontal line of the Plimsol mark. In summer zones, the ship can load up to this line in salt water. The vertical distance between the upper edges of S and T (and also between S and W) is l/48 of the summer draft of the vessel. The dates and limits of winter, summer and tropical zones are given in the loadline rules. The WNA mark, if applicable, if situated exactly 50 mm below the W mark (measured between their upper edges).

The vertical distance between the upper edges of the lines marked S and F, and also between T and TP, is the FWA of the ship.

AIR PIPES

Every tank on board ship must be provided with an air pipe; the purpose of providing an air pipe is to expel air from the tank during liquid filling operation and inlet air during liquid pump out operations. In other words, air pipes provide a passage way for inlet and expulsion of air during liquid movement, thus preventing Vacuum being formed in the tank.

The bore of the air pipe will much depend upon the volume of the tank to which it is fitted.

Every air pipe fitted to Double Bottom and deep tank which extends upto the shipside or any tank which may run up by the sea is always led above the Bulkhead (weather) deck.

Every air pipe leading from fuel tanks, cargo oil tanks, cofferdam having its opening above the weather deck must be of such height, where no danger will result from leakage of oil or its vapour.

The open end of the air pipes must be provided with closing arrangement, be fitted with weather tight closing arrangements, ball valve in the trunk of the pipe and spark arrester mesh on

the mouth of the air pipe, as required by the load line conditions assignment.

All exposed air pipes shall be of substantial construction, its height above the deck must be at the minimum 760 mm. in position - 1 and minimum 450 mm. In position 2; as far as possible, air pipes must be located in lee of the hatch / bulwark or such place where it has minimum exposure to damage.

SOUNDING PIPES

Every tank on board not readily accessible must be provided with a sounding pipe, other tanks which are accessible may be provided with gauge glass or any other means of finding depth of

liquid in the tank.

Sounding pipe as far as practical must be without bends and lead in the vicinity of tank suction I lowest part of the tank. Every sounding pipe must be protected against deck cargo damage, must be provided with means of water tight closing arrangements, incase of screw down covers, the cover must be secured with chain or any other arrangements to prevent the

cover from going adrift.

The minimum bore of the sounding pipe must be 32 mm, sounding pipes passing through refrigerated spaces having temperature of 0°C or minus must be to a minimum 65 mm.

In way of the lower end of the sounding pipe, where the sounding rod strikes the bottom of the tank, a striker plate must be fitted. The striker plate must be inspected and replaced as and when deemed necessary, each time the tank is entered for any purpose.

Every tank must be calibrated and be provided with tables I graph for volume I tons calculations in various conditions of trim and list.

BILGE WELL AND SUCTION ARRANGEMENTS

BILGE WELL IS A COMPARTMENT FITTED WITH SUCTION ARRANGEMENTS TO PUMP OUT ANY LIQUID THAT MAY FIND ITS WAY INTO THE CARGO COMPARTMENT.
BILGE WELL PROJECTS IN TUHEDOUBLE BOTTOM TANK, WITH ITS .0PENING FLUSHED TO THE TANK TOP, THE MARGIN PLATES MUST BE WATER TIGHT
BILGE IS DIVIDED INTO TWDCOMPAARTMENTS, THE FILTER BAY AND THE SUCTION BAY.
SUCTION BAY FIATTED WITH A STRUM BOX, THE SIDE WALLS OF THE STRUM BOX MUST BE PERFORATED, ATLEAAST 0NE SIDE MUST HAVE SLIDING OR HINGE OPENING ACCESS FOR INTERNAL CLEANING OF THE STRUM BOX.
SUCTION LINE MUST BE FITTED WITH A NON – RETURN VALVE.
SUCTIOAN LINE MUST NOT BE. LESS THAN 50 mm. INTERNAL DIAMETER.
EACH PERFORATION MUST BE 1 Cm.

PATENT STEEL HATCH COVERS

Patent steel hatch covers having direct securing arrangements, e.g. MacGregor Steel Hatches are a great improvement on the portable type previously described and are universally fitted for weather decks. They consist of plated covers stiffened by webs or stiffeners, watertightness being obtained by gaskets and clamping devices.

Securing cleats and cross joint wedges, together with suitable jointing material are to be fitted, the cleats are to be spaced to ensure weathertightness with a minimum of two per panel at the sides and with one arranged adjacent to each corner at the hatch ends. The cross joint wedges are spaced about 1.5 m apart.

The portable sections of folding covers are connected to one another and can easily and quickly be rolled into or out of position, leaving clear hatchways and decks. The normal practice is for the lengthwise opening of patent hatches but sideways opening hatches are found on some particular types of ships, e.g. OBO carriers, see pages 85 and 125. Patent steel hatch covers may be operated manually or hydraulically. The illustration shows a folding patent steel hatch cover.

The wheels at the sides of the hatch sections, eccentric rollers, are used for raising the hatch section clear of the coaming and for rolling it along the coaming trackway. As shown the axles of these wheels are so adjusted that when the hatch is in the closed position the weight is no longer borne by them. The jointing fits tightly on the coaming and the hatch is made completely weathertight by fitting and securing the cleats.

The roller is used when the hatch cover is pulled into its stowage position. It engages on the plate edge at the ends of the hatchway and the hatch section is turned into the vertical. Wires, chains or bars attached to the stub axles of these rollers at the centre of the wheel enable all the hatch sections to be drawn back and forth together.

The cross joints are made weathertight as shown with cross joint wedges.

HATCH COAMING

Hatch coaming is a steel structure welded on the weather deck, along the perimeter of the opening on the deck. On top of the coaming plate a bulb end flat bar is welded termed as the table top of the coaming.

The table top is mounted with a compression bar on Port and starboard side coaming, and bulb angle bar at the forward and aft end for providing surface of compression enable achieve weather

tightness of the hatch covers; a track way is mounted for providing a surface for movement of the pontoon eccentric wheels, and flat bar for housing of quick acting cleats.

The hatch coaming plates are adequately strengthened by stays welded at intervals of not exceeding two meters, on all the four sides of the coaming, in addition longitudinal stiffeners may be welded.

The weather deck is fitted with doubler I insert plates at each corner of the hatch opening.

The deck opening corners are rounded off to avoid point of stress concentration; the radius of the corner rounding within the region of 0.3 length from fore and aft end, must be not less than 305 mm, else where not less than 150 mm.

To achieve weather tight joint between the pontoon end and table top of the coaming, each pontoon houses rubber packing along its perimeter; the rubber packing is compressed against the

compression bar on the table top under the pressure of its own weight, additional pressure is exerted by the quick acting cleats and cross wedges; minimum Two quick acting cleats must be provided on each pontoon, the quick acting cleat must nit be more than 30 Cms, away from each corner.

As per load line rules, hatch coaming in position 1 must not be less than 600 mm, else where not less than 450 mm; however, to comply with factory act requirements the height of the coaming is usually not less than 760 mm.

The purpose of hatch coaming is to prevent any water from deck entering the cargo compartment or through the pontoon overlap end, hatch coaming also forms a barrier to prevent accidental fall of

personnel while working on deck.

Hatchways

Hatchways in the majority of dry cargo ships extend across the deck for approximately one-third of the beam. In special types of ship, e.g. container ships, colliers etc., much wider hatchways are fitted as will be seen from the separate cross-sections of these types.

Special arrangements must be made to compensate for the structural discontinuities caused by these large openings; insert plates of increased thickness may be required at the hatch corners as shown. The arrangement of hatch coaming and adjacent structure with rounded hatch corners is illustrated. Note that the hatch coaming should be extended beyond the corner to form a bracket. The deck opening corners should be well-rounded to a reasonable radius, or eliptical or parabolic in shape, to avoid a concentration of stress at these points.

The deck plating forms an important structural member, especially at the strength deck, in resisting longitudinal stress, but only the plating clear of the hatches can be considered in this respect. If hatchways are made unduly wide, the effective width of this plating is reduced and the thickness has to be increased in order that the cross—sectional area of the steel is maintained.

In addition to the plating, beams will also be cut at hatchways and the ends of the half beams will be connected to the hatch coamings and supported by deck girders. The deck girders are usually integral with the hatch coamings as illustrated. At the ends of the hatchways, in the case of transverse framing and at the sides in the case of longitudinal framing deep hatch end beams will be fitted to support the coamings. A pillar will often be placed near the hatch corners at the intersection of the deck girder and a strong beam.

Wednesday, 22 July 2015

BALLAST FW TANKS

Certain bulk carriers may be provided with ballast tanks on port and starboard side which do not extend up to the tank top, such tanks are termed as wing or top side tanks.

All ballast tanks must be fitted with filling lines arrangements, pumping out or decanting arrangements, air pipes, sounding pipes and man entry access way arrangements.

FRESH WATER TANKS

Every ship must be provided with Potable water tanks additionally wash water tanks may be provided.

These tanks location will vary with the size and type of ship.

OTHER FUEL OIL TANKS

Separate tanks for various grades of fuel oil 'i.e. Heavy oil, Diesel oil storage tanks, fuel oil settling tanks, day tank and lubrication oil tanks are provided on board. The location of these tanks on board will vary from ship to ship.

CARGO TANKS & BALLAST TANKS

CARGO TANKS

Cargo Tanks, generally speaking are referred to cargo compartments on board tanker or Gas Carrier.

The volume enclosed between the weather deck, inner bottom (Tank top) and between inner skin (Hull) of a tanker is transversely and longitudinally divided into several compartment termed as cargo tanks.

This type of arrangement is generally found on board product carriers, where various grades of liquid cargoes have to be carried on board.

Transverse and longitudinal bulkheads are extra strengthened by webs, deep frames, stringers etc., so is the tanks bottom and hull plating strengthened, this strengthening enables the bulkheads to

with stand the head pressure exerted by the liquid.

BALLAST TANKS

These are compartments on board all ships, dedicated for carrying Sea water as ballast for the purpose of stability & trim of the vessel. during the vessels unladen voyage.

Ballast tanks are located between the ship’s bottom plating and tank top, these tanks are termed as double bottom tanks. The volume forward of the collision bulkhead and abaft the aft bulk head are

termed as fore and aft peak tanks respectively.

In addition to the afore said tanks, certain modern ships such as container ships, bulk carriers and tankers vessels & OBO’s, side ballast tanks may be provided on the port and starboard side through the length of the vessel. These tanks are independent of the double bottom and peak tanks.

DEEP TANKS

Deep tanks are tanks on board ship in which liquid cargoes are transported.

Deep tanks may be found on board Tankers, they may also be constructed on board general cargo ships.

Deep tanks on board Tanker ships are generally located abaft the collision bulkhead. These tanks are only used for storing extra fuel on ships which make long international voyages, or calling at port where bunkers are not readily, or not at a competitive price.

Deep tanks extend through the depth and breadth of the ship abaft the collision bulkhead, in addition forward and aft of the deep tank a void space is retained known as the cofferdam.

The deep tanks and the cofferdam are sub-divided with one or more longitudinal bulkhead. Fuel heating and pumping system must be fitted.

On Board General cargo ships, deep tanks are of two types:

1. Dedicated liquid carrier deep tanks.

2. Multi-purpose deep tanks

1. DEDICATED DEEP TANKS

Location of the dedicated deep tanks are planned during the constructional stage of the ship.

In case of a single deck General cargo ship, deep tanks extend from the tank top to weather deck, this volume could be a part of the cargo hold or a entire small hold.

ln case of a Tween Deck General ship, Deep tank could be a part of the lower hold.

ln cases of dedicated Deep tanks in a tween deck ship, the man hole will be of the ﬂushed to deck, however, in case ofa single deck ship, flushed or coaming type of man hole may be found.

2. MULTI - PURPOSE DEEP TANKS

ln case of a single deck General cargo ship, deep tanks extend from the tank top to weather deck, this volume could be a part of the cargo hold or a entire small hold.

ln case of a Tween Deck General ship, Deep tank could be a part of the lower hold.

ln cases of Multi-purpose Deep tanks in a tween deck of a single deck ship, the access way will be of large hatch cover type , suitable for small general cargo operations.

GENERAL

In case of dedicated deep tanks, cargo heating coil arrangements could be open on the tank top or concealed under the tank top, however, in case of multi-purpose tanks, cargo heating system will

always be concealed under the tank top and bilge pumping arrangements must be provided.

ln both cases, extra strengthening of the Bulkheads, shipside and tank top must be provided; the tanks must be provided with sounding and air pipes.

Temperature may or may not be provided

ON BOARD GENERAL. CARGO SHIP - TWEEN / SINGLEDDECKER.

Deep Tanks" are specially designed compartments for carriage of Dry Cargoes, liquid cargoes or ballast, these tanks may be located in the Lower Hold in case of Tween Decker or extend throughout the depth of the cargo hold in case of Single Decker.

Deep Tanks may be designed for multipurpose use QR designated for liquids only. In case of multipurpose deep tanks, General Cargoes / Dry Bulk Cargoes can be loaded and stowed through large tank openings provided on the Tween Deck / weather deck; the closing arrangements is with heavy steel covers designed with suitable securing arrangement tor water tightness. The opening can be at Tween Deck level or on the Weather Deck.

In case of deep tank designated for liquids only, the tank opening design can be of flushed manhole type or tank access way of coaming type. In both cases the covers must be Water Tight.

ON BOARD TANKERS

The deep tank is generally located abaft the Collision Bulkhead and forward of the cargo tank.

A cofferdam is located Forward and Aft of the deep tank to avoid contamination in case of a leakage/puncture in the water tight bulk-head.

The deep tank is generally used for carriage of Ship’s fuel.

PARAMETERS OF DEEP TANK ON BOARD SHIP/GENERAL CARGO & TANKERS.

Deep Tanks may be divided by a center line bulkhead to form Port & Starboard tank. Deep tank tank is space confined between center line bulkhead and Hull plating on each side of the ship; Forward and Aft watertight bulkhead, and between Tank Top and Tween Deck or weather deck as the case may be.

The shipside frames are closely spaced in way of deep tanks in no case not more than 600 mm apart.

Tae Fore & Aft watertight bulkhead plates are thicker at the bottom than normal bulkhead, enable them withstand the head pressure exerted by the liquid.

The Fore & Aft bulkheads and center line bulkhead must he adequately strengthened with vertical and horizontal stiffeners to with stand the free surface effect.

The vertical stiffeners must be attached at the Deck Head & at the tank top with brackets / knees.

The Deep Tanks must be pumping arrangements & heating coils system.

The Deep Tanks, must be provided with Sounding pipe, Temperature pipe, & Air pipe, they must be fitted with water tight closing arrangements.

ln case of multipurpose deep tanks, hold bilge system must he provided.

DOUBLE BOTTOM TANKS

Volume enclosed between the ship's bottom up to the turn of the bilge, abaft the collision bulkhead and forward of the aft bulkhead and tank top in the cargo holds is termed as double bottom tanks. Double bottom tanks are identified numerically from forward to aft.

Double bottom tanks do not extend in way of the peak tanks and Main Engine room space.

Double bottom tanks are sub-divided longitudinally to form Port and Starboard Tank by water tight girders or walls of the duct keel, Double bottom tanks are divided by water tight floors.

Double bottom tanks are strengthened by bracket floors, solid floors, tank side brackets, inter coastal girders, center girder, longitudinal members which are located under the tank top and on the inner surface of the bottom plating, all these members jointly contribute in strengthening longitudinal and transversely the bottom structure of the ship.

Tank side brackets are fitted along the length of the double bottom tanks in way of the turn of the bilge.

Double bottom tanks are generally used for ballast water, fuel, fresh water / boiler feed water.

Every double bottom tank must be provided with air pipes, sounding pipes, filling and suction pipe line arrangements.

Naval Architecture

Monday, 3 April 2017

NA & Ship Co Quiz II

Thursday, 23 March 2017

NA & Ship Co Quiz I

Saturday, 14 January 2017

Topic - 17 Fore End Construction

Tuesday, 28 July 2015

STRUCTURAL PARTS OF THE HULL

STERN ARRANGEMENT

BEAMS & FRAMES

BULKHEADS

SHIPBOARD MEASUREMENTS

FREEBOARD

Monday, 27 July 2015

LOADLINES OF SHIPS

AIR PIPES

SOUNDING PIPES

BILGE WELL AND SUCTION ARRANGEMENTS

PATENT STEEL HATCH COVERS

HATCH COAMING

Hatchways

Wednesday, 22 July 2015

BALLAST FW TANKS

CARGO TANKS & BALLAST TANKS

DEEP TANKS

DOUBLE BOTTOM TANKS