The Floaters with ship shape hulls can be gathered into groups:-
a) Small Tankers up to 80 to 90,000 tonnes used typically as shuttle tankers from Export SALM to local refinery port such as Rotterdam or local port to local port for smaller transhipments which are often demanded by shallower waters.
b) Trading Tankers from crude supply locations such as Midle East, Gulf to a Refinery Port such as Rotterdam and return in ballast condition. The profile of the tankers shows the bulbous nose. This feature particularly elaborates there use. When loaded the nose is submerged and the profile presented is hydraulically aerodynamic. These ships are designed for optimum speed cruising when loaded to convey a cargo economically at reasonable speed from origon to market. When ballasted the nose still assist penetration through the water with the bulbous nose bow penetrating the water and being overflowed. Three size ranges exist as in the tabulation. Each range was derived to meet a requirement, Aframax, the 100,000 tonner was big enough to go most routes from origon to market. The Suezmax 200,000 tonner was as the name suggests related to a Suez canal maximum, this route gives the shortest time from origon to market. The VLCC 300,000 tonner is optimised for economy based on larger cargo around the Cape. These groupings have held strong but now other types are coming into the picture, a second Suez Canal may take larger ships and the Northern routes from the Artic will require another standardised design of hull for low temperature, ice conditions, bulbous nosses and ice don't go.together well.
The dominance of the ship shape floating hull for FPSO,s has often resulted from the perceived need to have a shortened project time from design to coming into operation. Many good Trading Tankers Hulls have become available and thus remove the time delay of a purpose build. this advantage is at the expense of the disadvantage that modules usually are supported from hard points in their base frame and that mates with a hull that is very much like a moniocoque box girder bridge, few hard points gaining its strength from sheet panels with minimal siffening but preformed to provide strength. We have a hull that flexs, hogs and sags on the waves matted to a module with a stiff base to ensue the components that it contains do not suffer the flexures of the hull.
The Diagram shows a standard tanker used for the transport of crude. It is this type of vessel most selected for an FPSO. This applies for new build and the schedule attractive conversion of an existing tanker.
Hulls of tankers are built to a generic requirement to various Class Certification requirements of ABS, Lloyds NK, DnV GL etc. The sizes are based on 3 categories, Afro Max Suez Max and VLCC the sizing is a indication of suitabilty to trade through, the Suez Canal, around the Cape, hence the Names
The Diagram shows a standard tanker used for the transport of crude modified to an FPSO. This illustrates features that are elaborated in 2b Moorings and Swivels and 2c Bow Ideal Hull
Besides Class certification are the Requirements of such organisations as MARPOL, Safety at Sea, Safety of Seamen etc. The impact of MARPOL gives the requirement for the isolation of ballast from Cargo and Isolation of cargo should the ships skin be breached. Compliance is acheived by Twin Skins as illustrated. Other Safety factors cover the requirements for life boats, saving equipment. International Regulation/Guidance is now concverened with Carbon Impact, collection of VOC from cargo vents, the use of Gas Fuel for Engines. The list of Requirements seems endless but from the methodical development of "The Safety Case" then its list of requirements can be built up.
The Diagram shows other ffeatures that must be taken into account. The standard tanker usually had a central piperack for the pipework connecting the cargo tanks. This rack needs to be extended to take in the Processs Pipework used to hook up the Modules
Another feature is the escape tunel which runs from stem to Stern. Support of these must be taken to the plate frames as beams, plates or spreader pads
Floaters is a broad reference to Hulls that Float,( some are ship shape, some are other shapes such as cylindrical, semi sub, submerged pontoon ) and are used for Production, Storage and Offloading, in short known as FPSO's.
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Index, Section 2 Supports,
a general understanding of Modules
Swivel Hi Lo Tide
Pipe Rack 2
1 _ Basic Tanker Hull
Modules on Hull All (FILEminimizer)
Diag 1, Typical Tanker
Diag 2, Hull often Constructed as Boxes
Diag 3, Hull with Typical Modules
Diag 4, An Arrangement of a Completed FPSO
Diag 5, Profile of a Completed FPSO.
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1,Outlines, Afra Suez VLCC Hulls
2, Hog and Sag of Hull
1 Tanker Construction
2 Tanker Module Styles
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