NEWS

Marine Winch Brake

This marine winch brake covers both the input brake and the primary brake.

Input brakes are automatic brakes on the drive motor shaft, and are required where electric (and some hydraulic) drives are used. Such drives usually have no means of holding position without the input brake and would otherwise just freely rotate and allow the mooring lines to pay out under their own weight. Electric motors, and some hydraulic motors, have a tendency to freewheel when power is off, allowing uncontrolled run out of the mooring line. To prevent this, they may be provided with automatic brakes on the drive motor shaft. These are known as input brakes and sometimes magnetic brakes. ISO 3730 requires all electric drive motors to be provided with an automatic braking system that has a holding capacity of 1.5 times the drum load. These input brakes are in addition to the primary winch brake.

The input brake is applied by springs when power is off. Power is required to activate the electro-magnets that release the input brake. Power is applied when the control lever is in the heaving or rendering position. In the event of power failure, the input brake remains applied. The brakes are therefore fail-safe.

Input brakes are not normally used as the primary brake for the winch as to do so would require all the components of the drive train, including the gearing, to be capable of resisting the brake rendering load of the winch.

Also, if the drum is left engaged and the brake band is set, both the drum brake and the input brake will work in unison and the mooring winch will not render at 60% of ship design MBL.

The primary brake secures the drum of the marine winch, and thus the mooring line, at the shipboard end when the ship is moored. The primary brake is designed to render before line loads become excessive to reduce the risk of mooring lines breaking. Winches that service multiple drums will always require a primary brake for each winch drum.

Ideally, a winch brake should hold and render within a very small range. Rendering should shed only enough load to bring the mooring line tension back to a safe level.

The winch brake holding load is set at 60% of ship design MBL.

Primary brakes for marine winch drum are generally band type. While disc type brakes are commonly used as the primary brake on high duty winches, such as those for anchor handling and to wage, they are not common on tankers. And disc brakes are commonly used as the primary brake for anchor handling and towage winches but few, if any, are used as an alternative to band brakes as primary brakes on mooring winches.  Disc brakes also are used more often for the input brake. Disc brakes use a calliper that applies friction to a disc. The calliper is generally power operated leading to greater precision in setting the brake loading. Disc brakes work equally well in either direction of rotation.