Windlass is used to collect, place anchor and anchor chain. The windlass is usually installed on the main deck of the fore and aft part of the ship for the purpose of anchoring and mooring.
The windlass is a mechanical device for throwing, lifting and winding cables, which is set at the head of the ship. The rollers on both sides of the sprocket can be used for winding up the cable. According to different power, windlass can be divided into manual windlass, electric windlass, electric hydraulic windlass and steam windlass. At present, electric hydraulic windlasses and electric windlasses are the main types of windlasses. In early oil tankers, steam windlasses were also used to prevent fire and explosion. In order to control the operation of the windlass, the power windlass is equipped with a master controller, which can carry out reversing operation and multi-level variable speed control.
Classifications and Uses of Windlass
The manual windlass is suitable for ships with anchor mass less than 250kg, and measures shall be taken to prevent the handle from hurting people.
The power source of the electric windlass is the motor, which drives the main shaft to rotate after multi-stage deceleration through the large and small gears in the reduction box. Due to the high requirement of reduction ratio, the reducer structure is relatively large, which is mainly used in small and medium-sized ships.
Electric hydraulic windlass is also called hydraulic windlass. The hydraulic pump is driven by the motor, and the generated oil pressure drives the oil motor, and then the windlass operates through the reducer (or without reducer). It has compact structure, small volume of power and transmission part, stable operation and good speed change performance, but it is widely used in modern large and medium-sized ships due to its high requirements of manufacturing technology and maintenance.
The steam windlass is driven by the steam engine, and the drum shaft is driven by the gear through the crank shaft. It is characterized by great power and simple structure. Warm up the cylinder in advance when using the steam windlass, and discharge the residual water vapor in the cylinder after use. When it’s cold, carry out sports car (keep idling) to prevent freezing.
All kinds of windlasses have the same function except for the different power part, which includes sprocket, winch drum, clutch and brake, etc. These functional components are arranged on the same power driven spindle. The winch drum (auxiliary drum) at the end of the main shaft generally rotates with the main shaft, and the sprocket is controlled by an independent clutch and brake. When the clutch is closed, the sprocket and the main shaft are locked together, and can rotate with the main shaft, so that the anchor chain can be twisted in or out. When the clutch is disengaged, the sprocket does not rotate with the main shaft, so it can be used for anchor or cable winch operation. The brake is used to stop the anchor chain or control the release speed. When the brake is tightened, the sprocket is fixed on the windlass body and cannot rotate. Generally, a double chain wheel windlass can be set on the ship. For large ships or ships with large spherical noses, due to the large spacing between the left and right anchor chains, two single chain wheel windlasses (or unilateral windlasses) separated from the left and right are usually set.
According to the layout, the windlass can be divided into horizontal windlass and vertical windlass. Horizontal windlass is widely used in modern transportation ships, and its main shaft is arranged horizontally. In order to facilitate the operation of mooring line and the adjustment of the force on the cable, modern ships often use the anchor mooring combination machine, which combines the anchor machine and the mooring winch. In addition to the auxiliary drum at the end of the main shaft, the main shaft of the windlass is also provided with a mooring winch (main drum), which is driven by the main shaft as well as the sprocket, and controlled by an independent clutch and brake. When the clutch is closed, the cable can be twisted in or released. After the cable is tightened, the brake is tightened to maintain the stress state of the cable without moving and pulling it to the cable pile.
The sprocket shaft of the vertical windlass is perpendicular to the horizontal plane, so the arrangement can reduce the deck area occupied by the windlass, which is often seen on warships.
There are also automatic windlasses and remote windlasses. The former is equipped with a chain length sensor in the automatic hydraulic windlass system. When the required chain is thrown out, the anchor will stop automatically; when the anchor is about to approach the chain barrel, it can slow down automatically, and when the dry anchor enters the chain barrel, it will stop automatically. The latter is a kind of windlass that can be operated remotely in the cab, and the operation of dropping and lifting the anchor can be operated remotely on the bridge.
The first stage – stow the anchor chain lying under the water. At this time, the anchor motor runs at full speed, and the load torque on the motor shaft is constant. The ship approaches the anchor point slowly under the pull of windlass chain. The shape of the suspension part of the chain remains unchanged.
The second stage – tightening the chain. At this time, the windlass tightens the anchor chain, the load moment on the motor shaft increases gradually, the rotation speed decreases, and the shape of the suspension part of the anchor chain changes until the anchor chain is straightened. The ship continued to move forward.
The third stage is the excavation of pulling anchor. After the anchor chain is tensioned, the inertia anchor pulling by the ship is excavated. If it can’t be pulled out, the motor will have a “locked rotor” phenomenon, that is, it will stop rotating under a large locked rotor current. In order to prevent the motor from burning out due to blocking, the motor is required to have “soft” mechanical characteristics, and the blocking torque is 2 times of the rated torque. In order to avoid too long locked rotor time (specified as 1 min), the driver can drive slowly and pull out the anchor by the force of the propeller.
The fourth stage is to collect the anchor and chain suspended in the water. After the anchor is unearthed, the load torque of the motor suddenly decreases and the speed of the motor also increases. With the shortening of the anchor chain, the load moment decreases gradually.
Stage 5 – pull the anchor into the anchor hole, and the motor runs at a low speed. When the anchor is inserted into the hole, the load moment of the motor increases due to the friction between the anchor and the steel plate of the anchor chain hole.
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