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The  alternatives to Swivels ( described in 2b Moorings, Swivels)introduces a number of modular alternatives that are connected together to make up an alternative to just a single point mooring and swivel.
Moduler Elements of Thruster,
left picture is of the Blades and Vari Pitch Hub Thruster Module,
the right information sheet shows how the
Thruster  Module is intergrated with the
Can Modules to form a Tunnel which is then spliced into the Hull.
The first of these is a Thruster to supplement a Swivel. A swivel mooring is subject to wind, current, tide and wave etc for its positioning of the floater. This may lead to the floater taking up a position unsuitable for its operation e.g. offloading to a shuttle tanker  lying astern, or for broaching to the wind but taking wave.  The first case occurs when  the  offloading to the shuttle tanker is  say 95% complete but wind and current change taking the  shuttle tanker to ride up on the FPSO. If the shuttle tanker can be kicked to lying astern then the offloading can be completed in safety. The use of a stern thrusters would allow this to happen without going astern using the main engine. Idealy the shuttle should go astern, most tankers use Deisels which are not happy in the slow speed reverse mode, another alternative is for the shuttle to have a steam turbine drive this has been a less favoured driver of recent years
thruster arrangement
thruster arrangement
Berg Thruster, blade alignment
Berg Thruster, blade alignment
C2V Where you see this, Click too View
C2V
C2V
Use of Thruster, for modfying position
Use of Thruster, for modfying position
1, Thrusterss Arrangement Windages of Hull
1, Thrusterss Arrangement Windages of Hull
2, Thruster Correction
2, Thruster Correction
MODULEitus
a general understanding of Modules 
Level 2
Level 3
Level 1
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