It should be remembered that the brake holding power is always greater than the heaving power and that once the brake starts to slip it is impossible to heave unless the force causing the slippage is reduced.
Risk of injury arising either from premature rendering or from winch not rendering at design pressure leading to over stressing of the moorings, is avoided by testing and adjusting to the correct rendering pressure during brake testing as per the relevant guidelines. Rendering of the brakes is a safety factor which also allows equating of tension in all the ropes / wires.
The primary brake should be set to hold 60% of the ship’s design MBL on the
- first layer in case of split drum and
- third layer in case of undivided winch drum.
Since brakes may deteriorate in service, it is recommended that new equipment be designed to hold 80% of the ship’s design MBL on the first layer in case of split drum and third layer in case of undivided winch drum but have the capability to be adjusted down to 60%.
PURPOSE: The main purpose of brake testing is to verify that the brake will render at a load less than the ship’s design MBL. Periodic testing of winch brakes is essential to assure a safe mooring. Oil, moisture, heavy rust on the brake lining or brake drum can reduce brake holding capacity in extreme cases by up to 75%. A band brake is designed to work in one direction only, so the line must always be reeled correctly onto the drum.
RENEWAL: Deterioration of the brake holding capacity will be caused by normal wear down of the brake linings. Brake linings on all ships should be renewed if the wear down is observed to be more than 40% (i.e., residual thickness is less than 60% of the original thickness).
On non-tank vessels, irrespective of the condition, brake linings of mooring winch must be renewed at every dry dock.
FREQUENCY: Brake Rendering Test shall be carried out after every occasion of renewing brake linings of a mooring winch.
Winch brake test must be carried out prior to new build vessel’s delivery and within 30 days after taking over of existing vessels, or Brake Rendering Test should be carried out at an interval not exceeding one year, or Master, in consultation with Chief engineer, should consider carrying out brake test when trading continuously in ports with berths exposed to seas/ swell or engaged in STS operations.
Instances where there is evidence of premature brake slippage or related malfunctions.
Installation of new mooring lines with different diameter to the existing lines
SETTINGS: The mooring winch brake should be set to render at 60% of the Ship design MBL on first layer in case of split drum and third layer in case of undivided winch drum.
If Ship design MBL is not provided by yard, the original “line MBL” at the time of Ship’s design (available in yard’s winch testing certificate) should be used as Ship design MBL.
Setting the brake lever for intended BRC:
Basis BRC, the hydraulic pressure for the jack is calculated and the brakes are set to render at that pressure.
When the brakes are new, at this pressure, there should still be a few threads (5 to 10) remaining in the brake lever when intended BRC is reached.
As the brakes wear down with use, the brake lever has to be tightened more to achieve the same BRC.
If the worn brake band is not renewed timely, the brake lever reaches its maximum limit and yet may not achieve the intended BRC.This leads to the risk of rope running out before intended BRC.
METHOD: The mooring winch brake test is carried out using ‘Brake Testing Kit’ or by measuring torque using ‘Torque Spanner’. Vessels are usually provided with ‘Brake Testing Kit.
PROCEDURE:
a) Brake rendering testing is to be carried out under the supervision of a responsible Officer designated by the Master.
b) Carry out a visual inspection of the brake band and any damage or failure should be rectified before any testing takes place.
c) Refer to the ‘Mooring winch manual’ for correct procedure of rigging the brake testing kit which can be different for various vessels.
d) Calculate ‘Jack Force and actual pressure required at hydraulic jack’ to reach ‘Brake Rendering Force’, at the first layer in case of split drum and third layer in case of undivided winch drum, as per the formula provided below.
e) Keep wooden grating or metal plate under hydraulic jack to uniformly spread weight.
f) Tighten the winch brakes and apply hydraulic jack pressure.
g) If slippage occurs at a pressure less than designed, the brake should be tightened & jack test reapplied.
h) If the recorded pressure corresponds to the design pressure the jack should be released and the test gear removed.
i) If slippage does not occur at the design pressure, the brake setting should be adjusted so the brake can render at design load.
MARKINGS: After testing, a 1 cm band shall be painted in a bright conspicuous colour around the brake lever to highlight the point of rendering.
Every winch shall then be marked with:
The date of the last brake test.
The primary brake holding load value as set (BHC).
The primary brake rendering value set (BRC).
The pressure gauge setting value where a brake is initially applied by a hydraulic assist.
In addition, the following shall also be marked on the winches:
The Reeling direction of the drum.
The heave and slack direction of the operating lever.
A stopper arrangement, e.g. locking nut on the threaded end, should not be used on the tightening screw. Stopper arrangements can impede the brake setting and reduce the brake holding load (See figure below).
Marking arrangements like jubilee clips, bands, and cable ties, which can easily slip/displace must not be used.
Example of Brake Rendering Marking on mooring winch
If mooring winches in a gas hazardous area are electrically powered, then the motors should be Ex ‘d’ (Flameproof) rated and regular insulation tests should be carried out and recorded.
