A ship on her unstoppable sail meets the need to rest only when her journey is at an end, she needs to halt at a port for cargo handling operations, or she has to anchor mid-sea due to several reasons. It might seem nothing is deadlier than the sea, yet anchoring or mooring a vessel poses another wave of challenges in seafarers’ safety. In this article we are going to navigate in deep about mooring winch operations and their challenges.
Generally, mooring refers to tethering a vessel to a permanent structure such as quays, jetties, piers etc. or a floating structure such as floating dock or buoy, another ship, to halt its free movement and keep it connected during loading and unloading operations. Thick ropes called mooring lines or hawsers are fixed to deck fittings on the vessel at one end to fittings such as bollards or rings at the other end for mooring operation. It is for adjusting the tension of these mooring lines and securing its shipboard end, a mechanical device called mooring winch is put to use, usually driven electrically. It is designed to conveniently handle halyards, adjust the mooring line length, keep the ropes under tension as per how tides favor, and wind up and wind out the lines as and when required.
Table of Contents
Parts of Mooring Winch
The various parts of a mooring winch and the role they play are as follows;
- Barrels- Also known as a winch drum, it is used for winding in and out the mooring lines or ropes that help tether the ship to a mooring. A mooring winch assembly can be equipped with several of it, wrapped around by cable or rope, as per the requirements of the ship.
- Warp end- It is a cylindrical fitting at the end of the winch, around which a wire rope is wound a few times to fasten or slacken it, manually holding the free end as the system rotates. It is most importantly used for aligning the ship along the berth by fastening one end of the rope to bollards onshore and the other end around a warp end. It is also auxiliary used for hauling ropes across a deck and handling additional mooring lines.
- Motor drive- The heart of the system lies in the motor drive that controls the barrel and warp end by a spur gear transmission system. The skeleton of the system is also equipped with a band brake, clutch and geared drives that facilitate in controlling drum movement such as halting it, forward and backward movement, and speeding it up or down by a reduction gear.
Common Problems Encountered in Mooring Winch Operation
Mooring operation, in general is a risky task just like so many shipping operations onshore and offshore. The Master of a ship needs to be aware of the tidal range and weather conditions and carefully pre plan the mooring operation before entering a port.
Common errors involve how winch breaks are inadequately set with poor maintenance of equipment and mooring decks. It is a common thing to install the break on the wrong load not following the correct mooring lines percentage of Ship Design MBL used on the winch.
There have been marine accidents such as large vessels breaking away from their moorings, concluding that brakes of mooring winches do not render before line parts. If the load on the mooring lines becomes overloaded beyond the safety standards, mooring winches band breaks can render and allow the line to shed this load before it potentially breaks and leads to the fatal “snap-back” incidents. The pre-set level known as Brake Holding Capacity, must be below the Minimum Breaking Load of the line to prevent against breaking.
Often, the braking line of the winch barrel is damaged due to using winch brakes to regulate the speed. A reduction gear should be used in its place instead.
Another common problem encountered in a mooring winch operation is that the winches may suddenly tighten or loosen when the ship is getting loaded and unloaded or in uneven weather condition. They can usually tension the wire up to 1.5 times the full load beyond which the barrel brake holds it when the power is shut off. Unless brake is overhauled, or recover wire until manually operated, wires may slacken. This may cause the ship to collide with the berth, consequently leading to several damages.
Mandatory regulations are there for the size, length and minimum breaking load of mooring lines as per IMO MSC/Circular 1175, and IACS Guidance. Good planning and maintenance is absolutely crucial to decide berthing approach, number of mooring lines to be used and mooring position. Despite all checks, winching and mooring lines can anytime pose a fatal threat to seafarers if a cloth along with a life gets tangled due to not maintaining proper distance while handling the ropes. Utmost care must be taken to ensure a healthy end or rest to the ship’s journey with a safe and secure mooring operation.
Adjusting Load Sensor in Mooring Winch
To sense the tension on the mooring winches during either loading and unloading or tidal range, load sensors are instilled in them.
Detection of Load: – The strain gauge in a load sensor produces varying voltages for varying loading condition. The different readings are displayed on the panel of winches. These gauges need to be calibrated timely as it compares the accuracy of the load cell (must be between 0.03% to 1%) with recognized standards. Various mathematical formulations calculate winch tension, drum diameter, rope diameter, pitch radius, jack distance (the distance between the center of shaft to where the hydraulic jack is positioned), jack load, jack piston area, and pressure of maximum brake holding.
All electric permit and proper awareness and precautions must be taken. The power to the winch should be cut off after putting the load sensor. The rope is slackened and a voltmeter is mounted. The reading should be 0 volt, if not to be adjusted accordingly as there is no load on the gauges. Now pressure is applied with the help of the jack on the clutch. When maximum pressure is reached, the voltmeter reading is to be checked. On releasing the pressure, reading should be 0V, if not, the load sensor trimmer must be re-adjusted for finer tuning.
Difference Between Winch And Windlass
A winch and windlass widely differ in structure and functions. Winch is used to wind in and out the mooring lines, while the apparatus of a windlass is such that it can move heavy weights such as anchor of a ship or fish trawls. It consists of a horizontal barrel which is rotated by the turn of a crank or belt, while a winch is affixed to one end wound by a cable. The weight it has to pull is attached to the opposite end. Usually located at the center of the foredeck, it helps to grasp the anchor rode and deposit the chain on the deck or below after pulling it out of water. The mooring line in case of a winch wraps the cylindrical portion of a winch, while in a windlass, it enters the forward end, passes around the cylinder and exits from the windlass housing. Winches can be categorized into automatic or manual tensioning by their control type, steam, hydraulic or electric by their drive type, by number of drums, split and undivided by the type of drums, band, disc, mechanical screw, spring applied by the type of brake. Windlass can be classified into horizontal and vertical windlass, though the term windlass generally refers to horizontal motion of a weight and the “capstan” is used for vertical motion. A windlass and capstan is combined to allow a personnel better control over manning the winch.
Both can be electrically or hydraulically powered and have a unique part to play in ship mooring operations as and when required. To ensure a safer mooring, checks on the mooring lines, anchors, locking bars, and cables of both winch and windlass must be performed so that locking bars can lock and secure the chain when vessel is at anchor and brakes don’t have to take full load of the cable. Only those concerned with the mooring procedures are expected to be onboard with full precautions and carry out these operations with their true mettle.