Bluebird Marine Systems Limited

 

AMPHIMAX BOW THRUSTERS STEERING FOR BEACH LANDINGS

 

 

 AMPHIBIOUS LAUNCH - AMPHIMAX - CAB - CHASSIS - DIESELS - FLOATATION - HYDRAULICS - LAUNCH SITE - MODEL 1/20 - TIMETABLE - TRACKS - TRAILER  - THRUSTERS - WHEELS

 

 

    

Hydraulic circuit diagram for a bow thruster installation

 

HYDRAULIC CIRCUIT - Where bow thruster propellers are underwater a hydraulic motor is a practical means of power transmission. Higher overall efficiency is achieved with piston-type hydraulic motors. These motors are said to be 10 - 18% more efficient than the vane or gear motors used in most thrusters. As a result, overall efficiency (in terms of thrust per input horsepower) could be 20 to 33% greater than competing products.

 

 

Handling a ship in currents, wind and tide is always a tricky affair. All these three factors can laterally shift the vessel from its course. A ship’s pilot has to keep an eye to these effects and constantly take remedial measures for safe navigation of the ship.

Berthing in heavy wind and tide situations is generally assisted by tugs – be it a towing tug or a checking tug or a tug that imparts athwartship force to counter lateral drift. These are additional to the already existing ship’s engines, rudder and thrusters (if installed).

 

We want to be able to steer AmphiMax onto our beach at right angle (ninety degrees) to the shoreline. Where we specify bow thrusters for steerage, this is because they have the qualities that we need in a convenient package that is designed to provide high thrust that is useful to us to ensure that our tracks achieve bite on the shingle positively.

The power (thrust) of a bow thruster generally depends upon the power of the motor. An 800 to 1000 HP Bow Thruster (BT) is effective enough to be fitted into a vessel having a LOA of 150-160 m and beam of 22-25 m with a GRT of about 10000-12000. It can easily counter offshore winds of 3-4 Beaufort (11 knots) while berthing. This is just an example, as we work from known data to calculate the requirements for our AmphiMax.

In areas of higher wind speed and ships having higher LOA and GRT, a more powerful bow thruster (BT) is required - the opposite is true with smaller ships in more sheltered locations.

 

 

WHAT IS A BOW THRUSTER?

 

A bow thruster or stern thruster is a transversal propulsion device built into, or mounted to, either the bow or stern, of a ship or boat, to make it more maneuverable. Bow thrusters make docking easier, since they allow the captain to turn the vessel to port or starboard side, without using the main propulsion mechanism which requires some forward motion for turning; indeed, the effectiveness of a thruster is curtailed by any forward motion due to the Coandă effect. A stern thruster is of the same principle, fitted at the stern. Large ships might have multiple bow thrusters and stern thrusters.

 

 

 

RABOESCH - Vane and contra-rotating tunnel based bow thrusters for ship models.

 

 

TUNNEL THRUSTERS

Large vessels usually have one or more tunnel thrusters built into the bow, below the waterline. An impeller in the tunnel can create thrust in either direction which makes the ship turn. Most tunnel thrusters are driven by electric motors, but some are hydraulically powered. These bow thrusters, also known as tunnel thrusters, may allow the ship to dock without the assistance of tugboats, saving the costs of such service. Ships equipped with tunnel thrusters typically have a sign marked above the waterline over each thruster on both sides, as a big cross in a red circle: (x).

Tunnel thrusters increase the vessel's resistance to forward motion through the water, but this can be mitigated through proper fairing aft of the tunnel aperture. Ship operators should take care to prevent fouling of the tunnel and impeller, either through use of a protective grate or by cleaning. During vessel design, it is important to determine whether tunnel emergence above the water surface is commonplace in heavy seas. Tunnel emergence hurts thruster performance, and may damage the thruster and the hull around it.

EXTERNAL BOW THRUSTERS

Instead of a tunnel thruster, boats from 30 to 80 feet (9 to 24 m) in length may have an externally mounted bow thruster. As its name suggests, an external bow thruster is attached to the bow, making it suitable for boats where it is impossible or undesirable to install a tunnel thruster, due to hull shape or outfitting. Externally mounted bow thrusters have one or more propellers driven by a small reversible electric motor which provides thrust in either direction. The added control provided by a bow thruster helps the captain to avoid accidents while docking.

WATERJET BOW THRUSTERS

A waterjet thruster is a special type of bow thruster that utilizes a pumping device instead of a conventional propeller. The water is discharged through specially designed nozzles which increase the velocity of the exiting jet. Waterjets generally have the advantage of smaller hull penetrations for an equivalent size thruster. Additionally, the higher exit velocity of the discharged water increases the relative efficiency as speeds of advance, or currents, increase, as compared to standard tunnel thrusters. Some waterjet bow thrusters can be configured to provide forward and aft auxiliary propulsion, or even full 360 degree thrust.

 

 

Blue Star Naxos

 

DOCKING - This is the Blue Star "Naxos" turning in port to dock.

 

 

BM SYSTEMS

 

In ....... to be completed ......

 

 

Twin impeller contra rotating tunnel bow thruster

 

CONTRA ROTATING IMPELLERS - Traditional single propeller systems generate thrust by accelerating water in the axis of the propeller shaft. However, the water discharged by the propeller also rotates. This is due, in part, to the friction between the surface of the propeller and the water. This rotational component does not produce thrust, but it does consume energy. By turning the propellers in opposite directions, the efficiency of the a thruster becomes 10 to 15% greater than that of single propeller systems. This has to be offset by frictional losses in the bearings and gears, but overall there is a gain with additional cost and complexity. Another method used to increase the efficiency of water (jet) pumps is a fixed stator. Torpedoes that have to travel at high speed use contra-rotating propellers for this reason.

 

 

 

 

 

LINKS & REFERENCE

 

http://www.marineinsight.com/marine-navigation/how-bow-thruster-is-used-for-maneuvering-a-ship/

http://www.lewmar.com/thrusters

http://loganclutch.com/

https://sideshift.com/

http://www.mitgroup.co.uk/bcs

http://www.thrusters.com/

http://www.thrusters.com/products/thrusters_hydraulic.shtm

http://www.hiseamarine.com/bow-thruster-1087.html

http://www.max-power.com/

http://www.nauticexpo.com/boat-manufacturer/bow-thruster-2706.html

 

 

 

 AMPHIBIOUS LAUNCH - AMPHIMAX - CAB - CHASSIS - DIESELS - FLOATATION - HYDRAULICS - LAUNCH SITE - MODEL 1/20 - TIMETABLE - TRACKS - TRAILER  - THRUSTERS - WHEELS

 

 

   

 

 

 

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