floating docks

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FLOATING DRYDOCKS

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TYPES OF DOCKS

FLOATING DRYDOCKS

SCOPE OF PRESENTATION:Types of floating docksComponents of floating docksMechanism of operationRating of floating docksInspections Freeboard rulesVessel transfer from floating docksAdvantages Disadvantages

TYPES OF DOCKS

** br 1762FLOATING DOCKS

PONTOON OR RENNIECAISSON , BOX OR ONE-PIECESECTIONAL

PONTOON OR RENNIE FLOATING DOCKHave continuous wing walls with sectional pontoons. The pontoon sections usually can be self docked by detaching them from the wings. This type dock is generally weaker in the longitudinal direction than the one-piece dock since only the wingwalls are effective for longitudinal strength. The structure of a Rennie type dock is generally heavier than the one-piece dock since double transverse bulkheads are needed at the gaps

** dockmaster manual by heger

CAISSON,BOX OR ONE PIECE FLOATING DOCKSBuilt in one piece, with continuous wing walls and pontoon. This type dock can be lighter and stronger than the other types since its full depth is effective in longitudinal bending. The capability to ocean tow a one-piece dock is easier to achieve although not all one-piece docks can be ocean towed.

** DOCKMASTER MANUAL BY HEGER

SECTIONAL TYPE FLOATING DOCKSA floating dock, which has no structural continuity over its length, is a sectional dockSome sectional docks are joined with locking logs which loosely aligns the sections but cannot take much force .Additionally, ballasting and deballasting operations can be very critical on these types of docks due to bending and deflection

** DOCKMASTER MANUAL BY HEGER

COMPONENTS OF FLOATING DOCKSMainly consists ofPontoons andWing walls

** BR 1762

Pontoons are the main supporting body that displaces the weight of the vessel & dry dock in order to lift the vessel using buoyancy. The Pontoon must distribute the concentrated load of the ship along the docks centerlineThe Wing walls provide stability when the pontoon is submerged and the longitudinal strength to distribute the irregular ship weight to the uniform buoyant support.

** BR 1762

DIAGRAMMATICAL REPRESENTATION OF FLOATING DOCK SECTION

** BR 1762

MECHANISM OF OPERATIONMade up of rectangular pontoon, divided into number of watertight tanks longitudinally and transversally surmounted by vertical wall on each side.Each of the pontoon tanks is fitted with an air escape pipe running to about six feet above the weather deck of the walls.Its arrangement is such that it limits the flooding of tanks and prevents the dock from sinking when the pumping equipment breaks down.Main pumps are usually fitted in the wall immediately above the main drain and are of centrifugal impeller type

** DOCK AND HARBOUR ENGINEERING BY H.P.OZA

MECHANISM OF OPERATION

SINKING THE DOCKSEA WATER THROUGH INLET VALVES MAIN DRAINPONTOON TANKS(VIA BRANCH PIPES)RAISING THE DOCKPUMP DISCHARGE VALVES OPENEDPUMPS STARTED UPTANKS PUMPED OUT

** BR 1762

RATING OF FLOATING DOCKSThe total load rating for a floating dock is usually determined by its buoyant capacity at a certain pontoon deck freeboard. The draft of the dock at the rated freeboard is called the operating draft. In addition to the load ratings, a floating dock may be limited by its stability. Usually, a kg versus weight curve is given as part of the certification.

** BR 1762

RATING OF FLOATING DOCKS

** BR 1762

FLOATING DRY DOCK INSPECTIONS

1. Internal structural inspection of ballast tanks and buoyancy chambers 2. Underwater Inspection (optional) 3. Testing of all main mechanical and electrical equipment 4. Witness a dock operation in which all mechanical equipment is run 5. Soundings around dock basin and entrance channel to dock 6. Leak Tests (if required) 7. Freeboard measurements with dock pumped to its minimum draft using main deballasting pumps.

** BR 1762

** DOCKMASTER MANUAL BY HEGER

FREEBOARD RULES:ABS RULESDNV RULESKR RULES

WING WALL FREEBOARD NOT LESS THAN 1MMINIMUM PONTOON FREEBOARD NOT LESS THAN 75 MMFREEBOARD TO PONTOON DECK NOT LESS THAN 300 MMFREEBOARD TO TOP DECK NOT LESS THAN 1MFREEBOARD TO PONTOON DECK NOT LESS THAN 300 MM AT CENTERLINE** ABS, DNV AND KR RULES FOR DESIGN

VESSEL TRANSFER TO AND FROM FLOATING DOCKSMost floating docks can be modified to allow longitudinal transfer to and from shoreA LIP or SHELF is usually provided at one end of the floating dry dock.During transfer, the docks LIP rests on shore side shelf.This keeps the rails on the dock aligned with the rails on the shore.

** US 2740367 PUBLISHED BY FREDERIC R HARRIS

During transfer, each compartment of the dry dock must be carefully ballasted to compensate for the vessels weight moving off of, or on to, the dock. The rate of transfer must be carefully controlled so as not to exceed the rate that compensating ballast can be added or removed. Detailed pumping plans should be prepared in advance of the operation to assure proper water levels at all times.

** US 2894472 PUBLISHED BY CHRISTOPHER J

One major benefit of using the floating dock for transfer, is the expensive cross transfer table and pit is not required. The dry dock itself can act as a table, aligning with any number of shore side berths.

** US 2977920 PUBLISHED BY FOSTER CHRISTOPHER

Some floating docks have been designed for side transfer. This obviously requires one side of the wing walls to be removable. Usually this wing is constructed in short segments so that it can be lifted on and off by the crane

** US 3709177 PUBLISHED BY CRANDALL

** DOCK AND HARBOUR ENGINEERING BY H.P.OZAADVANTAGESEASY MOBILITYCAN BE SOLD ON WORLD MARKET; RESALE VALUES HIGHCAN BE OPERATED WITH LIST OR TRIMCAN BE EASILY MOVED FOR DREDGINGCAN BE MOVED FROM LAND TO DEEPER WATER FOR DOCKING AND UNDOCKINGDOES NOT USE VALUABLE WATERFRONT REAL ESTATE

DISADVANTAGES

Routing of men and material is restricted to gangplank and/or crane service.

High maintenance is required on pumps, valves and steel structure.

Large tidal variations can complicate gangways, mooring etc.

REFERENCES:BR 1762DOCK AND HARBOUR ENGINEERING BY H.P. OZADNV RULESABS RULESKR RULESUS 2740367 PUBLISHED ON 03 APRIL 1956 BY FREDERIC R HARRISUS 2894772 PUBLISHED ON 14 JULY 1959 BY CHRISTOPHER JUS 2977920 PUBLISHED ON 04 APRIL 1961 BY FOSTER CHRISTOPHERUS 3709177 PUBLISHED ON 28 OCT 1973 BY CRANDALL DOCKMASTER TRAINING MANUAL BY HEGER DRY DOCK

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