Shaft system (shipbuilding)
The shaft system (engl. Marine shaft device) is the entirety of the device for transmitting the rotary movement / rotation power of the drive engine of a ship or boat on the propeller as well as for receiving the propeller thrust and its transfer to the hull. The shaft system can consist of one or more parallel drive trains.
construction
A ship shaft system usually consists of the pressure wave, the pressure bearing, bulkhead stuffing boxes, bearing bearings, intermediate shafts, the actual stuffing box and the propeller shaft, also called tail shaft. Furthermore, depending on the location of the engine room, shaft couplings (shell coupling) and the stern tube (stern bushing) are indirectly part of the construction of a shaft system. In the case of very long wave systems, a walk-in wave tunnel surrounds the wave system when crossing cargo holds or other ship spaces. The actual shaft is held by bearing bearings . With the exception of small boats, plain bearings are mostly used here. The rear bearing, the so-called stern tube bearing, is sealed against the sea water by a stern tube seal, for example by a stuffing box . Normally, a shaft consists of a straight line from the engine flywheel to the propeller. If space is limited, a gear can also be used to compensate for angular and / or height offset (see recreational shipping).
Gearboxes are often part of the shaft system. These serve to reduce the engine speed, since speeds below 200, if possible even below 100 revolutions per minute are aimed for for a favorable drive efficiency . In addition, the gearboxes often have additional drives for operating generators or pumps.
In complex systems, especially in military shipbuilding , the gearboxes of the shaft system play a central role, as several motors and possibly turbines with very different speeds have to be switched to one or more shafts.
The term “shaft system” has only been used in everyday language since other types of propulsion such as jet drives , outboard motors , propeller gondolas or Z-drives have been used in ships and boats in order to be able to differentiate the shaft system as a “classic” type of drive from the other types of drive .
Advantages and disadvantages of wave systems
The majority of all ships are still equipped with shaft systems today. This is due to the fact that the direct transmission of the rotary power causes very little power loss. Only about 1 percent of the transferred power is "lost" in the form of storage heat. With single gears, the losses are still very low at 2-3 percent. In comparison, a Z-gear such as the Schottel rudder propeller already has 5 percent power loss.
The shaft system does not normally include any maneuvering devices, such as B. Rudder . Other drive systems without a shaft system have this integrated (see propeller pod , Voith-Schneider drive ).
Disadvantages of wave systems are that they change direction and that they sometimes have a very pronounced wheel effect .
To change the direction of rotation, the so-called reversing, either the motor itself or the gearbox must be reversible or the propeller must be a controllable pitch propeller. Reversing the motors is usually associated with high loads on the motor and a time delay (quite a few minutes). Variable pitch propellers and gears for reversing are expensive to purchase.
In shaft systems with two propellers, the direction of rotation of the two propellers is set in such a way, usually in opposite directions, that there is almost no wheel effect and maneuverability can be significantly improved.
Recreational boating
In recreational shipping, the wave system is divided into three different designs:
- L-drive - the inboard motor transfers its power directly aft via the drive shaft to the propeller, possibly via a gearbox,
- V-drive - the inboard motor transmits its power with a first drive shaft to the front to a deflection gear and from there to the propeller,
- Saildrive - a compact system that is used in motor and sailing yachts with low propulsion power.
photos
Scheme of a CODOG system
Scheme of an L-drive of a sailing yacht
Part of a single-shaft system on a ferry ship that is visible from the outside
See also
literature
- Ramon Gliewe (Ed.): Seemannschaft: Handbuch für den Yachtsport , 26th edition, Delius Klasing Verlag, Bielefeld 2003, ISBN 3-7688-0523-9 , page 140
- K. van Dokkum: Ship knowledge , 2nd edition, Dokmar, ISBN 90-806330-6-2