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Where are stabilising fins fitted? How it works controlling ships motion ?

Stabilising fins are fitted to ship's sides below the waterline to reduce rolling of the hull by wave action. The fins achieve this by imposing an equal and opposite motion. Retractable fins of aerofoil section use the forward velocity of the ship to create this opposing motion. As the ship rolls to starboard, the starboard fin is set by a gyroscope signal so that the leading edge of the fin is set above the axis of tilt, giving an upward thrust. The port fin is set in the opposite tilt, with its leading edge below the axis of tilt, giving a downward thrust, and vice versa when the ship rolls to port.

Fin stabiliser
Sketch of fin stabiliser set up.

The purpose of the tail flap on stabiliser fins is to give the fin a more pronounced restoring torque action than if it were a plain surface. The angle of operation of the main fin is 20 degrees at around 15 knots and 11 degrees at around 24 knots. This is to ensure reasonable fin loading.

The angle of operation of the tail flap is 30 degrees. The hydraulic pressure used to house and extend the fin is around 70 80 bar. and the hydraulic pressure used to alter the fin angle is around 30 bar.

What instrument is used to sense the motion of the ship and then send a signal to the fin controls? : The instrument used to sense the angle of the ship and then send a signal to the fin controls is the roll sensor unit.

The panel fitted to the bridge to monitor fin position is a SOLAS panel, a positive light system to indicate if it is housed or extended. Note: this should also be backed up by visual checks.



Operational guideline for various auxiliary machinery described here:
Related Info:

  1. Compressed Air Systems for various shipboard operations
  2. The main aim of a compressor, as the name suggests, is to compress air or any fluid in order to reduce its volume. Some of the main applications of compressors onboard ships are main air compressor, deck air compressor, AC compressor and refrigeration compressor. Failure to start or control air compressor can be inconvenient, costly and can carry risks, which need to be managed.....

  3. Marine air compressors working principles
  4. Control or instrument air supplies have particular requirements with regard to being moisture and oil free and without impurities. A special type of oil-free compressor may be used to supply control air or it may be treated after delivery from an ordinary air compressor. This treatment results in the air being filtered and dried in order to remove virtually all traces of oil, moisture and any atmospheric impurities.....

  5. Coolers at sea- Shell and tube type coolers and plate type coolers
  6. Heat exchangers on board ship are mainly coolers where a hot liquid is cooled by sea water. There are some instances where liquid heating is required, such as heavy fuel oil heaters and sea water heaters for tank cleaning. Although being heat exchangers, the main condenser for a steam ship and the evaporator/distiller are dealt with separately .....

  7. Distillation system- Production of distilled water for ships use - The evaporation process
  8. Distillation is the production of pure water from sea water by evaporation and re-condensing. Distilled water is produced as a result of evaporating sea water either by a boiling or a flash process. This evaporation enables the reduction of the 32000 parts per million of dissolved solids in sea water down to the one or two present in distilled water. The machine used is called an 'evaporator', although the word 'distiller' is also used.....

  9. Oily water separator and filter unit for 15 parts per million purity
  10. Oil/water separators are used to ensure that ships do not discharge oil when pumping out bilges, oil tanks or any oil-contaminated space. International legislation relating to oil pollution is becoming more and more stringent in the limits set for oil discharge.....

  11. Sewage treatment on board- biological and chemical sewage treatment plant
  12. The discharge of untreated sewage in controlled or territorial waters is usually banned by legislation. International legislation is in force to cover any sewage discharges within specified distances from land. As a result, and in order to meet certain standards all new ships have sewage treatment plants installed.....

  13. Incinerator for ships
  14. Stricter legislation with regard to pollution of the sea, limits and, in some instances, completely bans the discharge of untreated waste water, sewage, waste oil and sludge. The ultimate situation of no discharge can be achieved by the use of a suitable incinerator. When used in conjunction with a sewage plant and with facilities for burning oil sludges, the incinerator forms a complete waste disposal package.....



Marine machineries - Useful tags

Marine diesel engines ||Steam generating plant ||Air conditioning system ||Compressed air ||Marine batteries ||Cargo refrigeration ||Centrifugal pump ||Various coolers ||Emergency power supply ||Exhaust gas heat exchangers ||Feed system ||Feed extraction pump || Flow measurement || Four stroke engines || Fuel injector || Fuel oil system || Fuel oil treatment ||Gearboxes || Governor || Marine incinerator || Lub oil filters || MAN B&W engine || Marine condensers || Oily water separator || Overspeed protection devices || Piston & piston rings || Crankshaft deflection || Marine pumps || Various refrigerants || Sewage treatment plant || Propellers || Power Plants || Starting air system || Steam turbines || Steering gear || Sulzer engine || Turbine gearing || Turbochargers || Two stroke engines || UMS operations || Drydocking & major repairs || Critical machinery || Deck machineries & cargo gears || Control and instrumentation ||Fire protection ||Engine room safety ||






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